EVOLUTIONARY BIOLOGY: ON THE EVOLUTION OF PHYTOPLANKTON

http://scienceweek.com/2004/sa040910-1.htm

ScienceWeek EVOLUTIONARY BIOLOGY: ON THE EVOLUTION OF PHYTOPLANKTON

The following points are made by P.G. Falkowski et al (Science 2004 305:354):

1) Coined in 1897, the term "phytoplankton" describes a diverse, polyphyletic group of mostly single-celled photosynthetic organisms that drift with the currents in marine and fresh waters (1). Although accounting for less than 1% of Earth's photosynthetic biomass, these microscopic organisms are responsible for more than 45% of our planet's annual net primary production. Whereas on land, photosynthesis is overwhelmingly dominated by a single clade (the Embryophyta) containing nearly 275,000 species, there are fewer than 25,000 morphologically defined forms of phytoplankton; however, they are distributed among at least eight major divisions or phyla.

2) Numerically, the vast majority of phytoplankton in the contemporary oceans is composed of cyanobacteria, the only extant prokaryotic group of oxygenic photoautotrophs. The basic photosynthetic apparatus in all cyanobacteria consists of two photochemical reaction centers, designated Photosystem I (PSI) and PSII (3). PSII oxidizes water and passes the electrons through a cytochrome b6/f complex to PSI, while simultaneously creating a cross-membrane proton gradient that is used to generate adenosine 5'-triphosphate (ATP). PSI, operating in series with PSII, generates a biochemical intermediate with a sufficiently low redox potential to drive the enzymatic reduction of CO2 to form organic molecules. Because water provided a virtually infinite supply of reductant for carbon fixation (4), within several hundred million years oxygenic photoautotrophs spread across the sunlit surface of the planet, making possible the oxidation of Earth's surface oceans and atmosphere 2.4 billion years ago (Ga) (5).

3) Oxygenic photosynthesis appears to have evolved only once, but it subsequently spread via endosymbiosis to a wide variety of eukaryotic clades. The earliest oxygenic photosynthetic eukaryotes are thought to have arisen from the wholesale engulfment of a coccoid cyanobacterium by a eukaryotic host cell that already contained a mitochondrion. The engulfed cyanobacterium would become a membrane-bounded organelle called the "plastid". The mitochondrion and plastid are the only two organelles that appear to have been appropriated via endosymbioses. Gene loss through time essentially reduced both symbionts to metabolic slaves within their host cells.

4) A schism early in the evolution of oxygenic eukaryotic photoautotrophs gave rise to two major plastid lineages. One group, united by the use of chlorophyll b as an accessory pigment, is overwhelmingly dominated by the green algae and their descendants, the land plants. Collectively, this "green" plastid lineage is much more closely related by plastid phylogeny and photosynthetic physiology than by the evolutionary history of the host cells. The second lineage includes the red algae (rhodophytes), which retain the most features of cyanobacterial pigmentation, and a diverse set of phytoplankton and seaweeds whose plastids (but again, not their host cells) are evolutionarily derived from rhodophytes. With the exception of the red algae themselves, members of this "red" plastid lineage utilize chlorophyllide c and its derivatives as accessory photosynthetic pigments. Of the eight major eukaryotic phytoplankton taxa in the contemporary ocean, all but one possess "red" plastids. In contrast, with the minor exception of some soil-dwelling diatoms and xanthophytes, all terrestrial algae and plants have "green" plastids.

5) In summary: The community structure and ecological function of contemporary marine ecosystems are critically dependent on eukaryotic phytoplankton. Although numerically inferior to cyanobacteria, these organisms are responsible for the majority of the flux of organic matter to higher trophic levels and the ocean interior. Photosynthetic eukaryotes evolved more than 1.5 billion years ago in the Proterozoic oceans. However, it was not until the Mesozoic Era (251 to 65 million years ago) that the three principal phytoplankton clades that would come to dominate the modern seas rose to ecological prominence. In contrast to their pioneering predecessors, the dinoflagellates, coccolithophores, and diatoms all contain plastids derived from an ancestral red alga by secondary symbiosis.

References (abridged):

1. P. G. Falkowski, J. A. Raven, in Aquatic Photosynthesis (Blackwell Scientific, Oxford, 1997), p. 375

2. C. Field, M. Behrenfeld, J. Randerson, P. Falkowski, Science 281, 237 (1998)

3. Structural and sequence analyses indicate that the reaction center of PSII is derived from purple nonsulfur bacteria, whereas that from PSI is derived from green sulfur bacteria, neither of which can split water to form oxygen (81)

4. J. A. Raven, P. G. Falkowski, Plant Cell Environ. 22, 741 (1999)

5. J. Farquhar, H. Bao, M. Thiemens, Science 289, 756 (2000)

Science http://www.sciencemag.org

--------------------------------

Related Material:

ON PHYTOPLANKTON

The following points are made by Jed Fuhrman (Nature 2003 324:1001):

1) With the sequencing of microbial genomes now almost routine in some circles, one could be forgiven for feeling a little jaded. It is possible to lose sight of just how much can be learned from such an exercise. But recent reports powerfully demonstrate how genomic studies can lead to a new understanding of biodiversity, ecology, biological efficiency and biogeochemistry.

2) About half of global photosynthesis and oxygen production is accomplished by single-celled planktonic organisms (phytoplankton) that live in the top layer of the ocean, where enough light penetrates to support their growth. The most plentiful of these are the cyanobacteria -- tiny, chlorophyll-containing phytoplankton that have no membrane-bound nucleus. There are two basic types. The Synechococcus strains have a diameter of about 0.9 microns and were discovered to be abundant in seawater in 1979. With a diameter of about 0.6 microns, meanwhile, the Prochlorococcus strains are the smallest of all the phytoplankton; they are also the most abundant, yet were discovered only 15 years ago.

3) The complete genomes of three strains of Prochlorococcus and one strain of Synechococcus have recently been sequenced and analyzed. The results are remarkable for what they show not only about the differences between these close relatives, but also about the extent to which some strains economize on DNA. Indeed, two of the Prochlorococcus strains have genomes so small -- about 1.7 million base pairs -- that they might represent the minimal genome of an oxygen-generating, photosynthetic organism.

4) Why economize on DNA? A genome represents the complete genetic repertoire of an organism: it contains specifications for all the machinery needed to create the organism and to regulate its operation, growth and reproduction. Control of genome size involves a trade-off between efficiency and versatility. A small genome reduces the amount of extra "baggage" that must be maintained and propagated, but also limits an organism's ability to exploit different resources. Larger genomes provide for this possibility, and also permit back-up should a gene be damaged or lost. But they require more material and energy to maintain.

Nature http://www.nature.com/nature

--------------------------------

DEFENSE MECHANISMS IN PHYTOPLANKTON

The following points are made by Victor Smetacek (Nature 2001 411:745):

1) Forests and algal *blooms fix approximately the same amount of carbon (a few grams per square meter per day), because both are based on essentially the same photosynthetic machinery fuelled by *chlorophyll-alpha in *chloroplasts, the descendants of free-living *cyanobacteria that have since evolved into plant organelles by *endosymbiosis. Chloroplasts provide their host cells with food in return for resources and protection. The range of defense systems in phytoplankton is only now coming to light.

2) The size range of phytoplankton spans 3 orders of magnitude, but that of its predators spans 5 orders of magnitude, from micron-scale *flagellates to shrimp-sized krill. Pathogens (viruses and bacteria) pose a further challenge. Most predators and pathogens of phytoplankton feed or infect selectively. Smaller predators hunt individual cells, whereas larger predators use feeding currents, mucous nets, or elaborate filters to collect phytoplankton en masse. Captured cells are pierced, ingested, engulfed, or crushed, but have evolved specific defense measures. The phytoplankton can escape by swimming or by mechanical protection; mineral or tough organic cell walls ward off piercers or crushers. In adapting to the deterrence of predators, phytoplankton cells have increased in size, formed large chains and colonies, or grown spines. Noxious chemicals also provide defense.

Nature http://www.nature.com/nature

--------------------------------

Notes by ScienceWeek:

phytoplankton: Small, usually microscopic, aquatic plants capable of photosynthesis; e.g., unicellular algae. Phytoplankton and plankton are not equivalent. The term "plankton" is a general designation for various drifting microscopic aquatic organisms in the upper regions of the oceans, both photosynthetic and non-photosynthetic.

blooms: In this context, the term "bloom" refers to an explosive increase in the density of phytoplankton within an area.

chlorophyll-alpha: (chlorophyll-a) Chlorophylls are magnesium complexes of various closely related porphyrins or chlorins. Chlorophylls a and b are dihydroporphyrins.

chloroplasts: The chloroplasts containing several photosynthetic pigments (chlorophylls). Chloroplasts are found in all photosynthetic plant cells, but not in photosynthetic prokaryotes (i.e., not in cells without membrane-bound organelles). The typical higher plant chloroplast is lens-shaped, approximately 5 microns across the larger dimension, and the number of chloroplasts per cell can vary from 1 to 100 depending on the type of cell. A mature chloroplast is typically bounded by two membranes, an inner membrane and an outer membrane, the membranes possessing significantly different chemical constituents. In addition to a number of enzymes involved in photosynthesis, chloroplasts also contain in their interior a circular DNA molecule and protein synthetic machinery typical of prokaryotes. The current consensus is that chloroplasts may have originated from *cyanobacteria that became endosymbionts.

cyanobacteria: A phylum of bacteria characterized by blue-green (cyan) photosynthetic pigments, abundant in a variety of habitats, particularly in fresh water and soil. Cyanobacteria are responsible for generating a large portion of the free oxygen in the Earth's atmosphere. They apparently produced stromatolite limestone deposits, as well as the bulk of modern petroleum deposits. (Stromatolites are laminated calcareous microbial fossil deposits formed principally by cyanobacteria and algae.)

endosymbiosis: An arrangement in which one organism lives inside another organism, but the term is usually restricted to arrangements of mutual benefit, thus not including parasite-host relationships. A number of eukaryotic cell organelles (including mitochondria) are believed to have originated from endosymbiotic relationships between eukaryotic cells and simpler cells.

flagellates: Organisms possessing one or more flagella. A flagellum is a long threadlike extension providing locomotion for a cell.

ScienceWeek http://scienceweek.com

Fossil reveals oldest live birth

Rebecca Morelle Science reporter, BBC News

A fossil fish uncovered in Australia is the oldest-known example of a mother giving birth to live young, scientists have reported in the journal Nature.

The 380 million-year-old specimen has been preserved with an embryo still attached by its umbilical cord.

The find, reported in Nature, pushes back the emergence of this reproductive strategy by some 200 million years.

Until now, scientists thought creatures from these times were only able to develop their young inside eggs.

When I looked at it, my jaw dropped. I said we are onto something big here Prof John Lane, Museum Victoria

Before this find, the earliest evidence for this form of reproduction came from reptile fossils dating to the Mesozoic Era (248 to 65 million years ago)

The team said the latest discovery had a remarkably advanced reproductive biology, similar to modern sharks and rays.

The extremely well-preserved fossil represents a new species of "placoderm" fish.

The placoderms were an incredibly diverse group and are thought to be the most primitive known vertebrates with jaws.

These armoured fish dominated seas, rivers and lakes throughout the Devonian Period (420-360 million years ago).

This latest placoderm specimen, which measures about 25cm (10in) in length, was found in the Gogo area of Western Australia in 2005 by a team led by John Long from Museum Victoria.

The fossil was found in Western Australia

Close examination revealed that the team had unearthed something unusual.

Professor Lane said: "When I looked at it, my jaw dropped. I said: 'we are onto something big here'."

The team found an embryo and an umbilical cord, which had been exquisitely preserved along with the female fish.

The scientists have named it Materpiscis attenboroughi, in honour of the naturalist Sir David Attenborough, who first drew attention to the Gogo fish fossil sites in the 1970s.

Sir David told the team that he was "very very flattered" to have had his name given to such an "astonishing creature".

The discovery prompted the researchers to return to another fossil that they had unearthed in 1986.

Close investigation revealed that this too contained evidence of live births - it contained three embryos.

Professor Lane said: "After we saw this, we realised we had totally nailed it, everyone was convinced that this creature bore live young."

Until the latest fossil find, scientists thought life forms that existed during these times had only evolved to reproduce using externally fertilised eggs - a primitive version of the way fish spawn today.

Now, however, the team believes this ancient species bore live young through internal fertilisation (viviparity).

Dr Long commented: "This is not only the first time ever that a fossil embryo has been found with an umbilical cord, but it is also the oldest known example of any creature giving birth to live young.

"The existence of the embryo and umbilical cord within the specimen provides scientists with the first ever example of internal fertilisation - or sex - confirming that some placoderms had remarkably advanced reproductive biology.

He added: "This is a world first fossil find, and it opens up a window into the developmental biology of an entire extinct class of organisms."

Commenting on the paper, Zerina Johanson, a palaeontologist at London's Natural History Museum, said: "It is extremely rare to find preservation like this in the fossil record. This new discovery extends the record of viviparity back almost 200 million years in the fossil record.

"Placoderms represent the most primitive group of jawed vertebrates, so this work shows that the capacity for internal fertilisation and giving birth to live young evolved very early during vertebrate history."

http://news.bbc.co.uk/2/hi/science/nature/7424281.stm

Human Common Ancestor??

Hominid Species

Sahelanthropus tchadensis Orrorin tugenensis Ardipithecus ramidus Australopithecus anamensis Australopithecus afarensis Kenyanthropus platyops Australopithecus africanus Australopithecus garhi Australopithecus aethiopicus Australopithecus robustus	Australopithecus boisei Homo habilis Homo georgicus Homo erectus Homo ergaster Homo antecessor Homo heidelbergensis Homo neanderthalensis Homo floresiensis Homo sapiens sapiens
Timeline

Introduction

Hominid or hominin?

Some scientists use a broader definition of Hominidae which includes the great apes, and instead call the group I am discussing "hominins". For a good discussion of the hominid/hominin terminology issue, read this article by Lee Berger.

The word "hominid" in this website refers to members of the family of humans, Hominidae, which consists of all species on our side of the last common ancestor of humans and living apes. Hominids are included in the superfamily of all apes, the Hominoidea, the members of which are called hominoids. Although the hominid fossil record is far from complete, and the evidence is often fragmentary, there is enough to give a good outline of the evolutionary history of humans.

The time of the split between humans and living apes used to be thought to have occurred 15 to 20 million years ago, or even up to 30 or 40 million years ago. Some apes occurring within that time period, such as Ramapithecus, used to be considered as hominids, and possible ancestors of humans. Later fossil finds indicated that Ramapithecus was more closely related to the orang-utan, and new biochemical evidence indicated that the last common ancestor of hominids and apes occurred between 5 and 10 million years ago, and probably in the lower end of that range (Lewin 1987). Ramapithecus therefore is no longer considered a hominid.

The field of science which studies the human fossil record is known as paleoanthropology. It is the intersection of the disciplines of paleontology (the study of ancient lifeforms) and anthropology (the study of humans).

Hominid Species

The species here are listed roughly in order of appearance in the fossil record (note that this ordering is not meant to represent an evolutionary sequence), except that the robust australopithecines are kept together. Each name consists of a genus name (e.g. Australopithecus, Homo) which is always capitalized, and a specific name (e.g. africanus, erectus) which is always in lower case. Within the text, genus names are often omitted for brevity. Each species has a type specimen which was used to define it.

Sahelanthropus tchadensis

This species was named in July 2002 from fossils discovered in Chad in Central Africa (Brunet et al. 2002, Wood 2002). It is the oldest known hominid or near-hominid species, dated at between 6 and 7 million years old. This species is known from a nearly complete cranium nicknamed Toumai, and a number of fragmentary lower jaws and teeth. The skull has a very small brain size of approximately 350 cc. It is not known whether it was bipedal. S. tchadensis has many primitive apelike features, such as the small brainsize, along with others, such as the brow ridges and small canine teeth, which are characteristic of later hominids. This mixture, along with the fact that it comes from around the time when the hominids are thought to have diverged from chimpanzees, suggests it is close to the common ancestor of humans and chimpanzees.

Orrorin tugenensis

This species was named in July 2001 from fossils discovered in western Kenya (Senut et al. 2001). The fossils include fragmentary arm and thigh bones, lower jaws, and teeth and were discovered in deposits that are about 6 million years old. The limb bones are about 1.5 times larger than those of Lucy, and suggest that it was about the size of a female chimpanzee. Its finders have claimed that Orrorin was a human ancestor adapted to both bipedality and tree climbing, and that the australopithecines are an extinct offshoot. Given the fragmentary nature of the remains, other scientists have been skeptical of these claims so far (Aiello and Collard 2001). A later paper (Galik et al. 2004) has found further evidence of bipedality in the fossil femur.

Ardipithecus ramidus

This species was named in September 1994 (White et al. 1994; Wood 1994). It was originally dated at 4.4 million years, but has since been discovered to far back as 5.8 million years. Most remains are skull fragments. Indirect evidence suggests that it was possibly bipedal, and that some individuals were about 122 cm (4'0") tall. The teeth are intermediate between those of earlier apes and A. afarensis, but one baby tooth is very primitive, resembling a chimpanzee tooth more than any other known hominid tooth. Other fossils found with ramidus indicate that it may have been a forest dweller. This may cause revision of current theories about why hominids became bipedal, which often link bipedalism with a move to a savannah environment. (White and his colleagues have since discovered a ramidus skeleton which is about 45% complete, but have not yet published on it.)

More recently, a number of fragmentary fossils discovered between 1997 and 2001, and dating from 5.2 to 5.8 million years old, have been assigned first to a new subspecies, Ardipithecus ramidus kadabba (Haile-Selassie 2001), and then later as a new species, Ardipithecus kadabba (Haile-Selassie et al. 2004). One of these fossils is a toe bone belonging to a bipedal creature, but is a few hundred thousand years younger than the rest of the fossils and so its identification with kadabba is not as firm as the other fossils.

Australopithecus anamensis

This species was named in August 1995 (Leakey et al. 1995). The material consists of 9 fossils, mostly found in 1994, from Kanapoi in Kenya, and 12 fossils, mostly teeth found in 1988, from Allia Bay in Kenya (Leakey et al. 1995). Anamensis existed between 4.2 and 3.9 million years ago, and has a mixture of primitive features in the skull, and advanced features in the body. The teeth and jaws are very similar to those of older fossil apes. A partial tibia (the larger of the two lower leg bones) is strong evidence of bipedality, and a lower humerus (the upper arm bone) is extremely humanlike. Note that although the skull and skeletal bones are thought to be from the same species, this is not confirmed.

Australopithecus afarensis

A. afarensis existed between 3.9 and 3.0 million years ago. Afarensis had an apelike face with a low forehead, a bony ridge over the eyes, a flat nose, and no chin. They had protruding jaws with large back teeth. Cranial capacity varied from about 375 to 550 cc. The skull is similar to that of a chimpanzee, except for the more humanlike teeth. The canine teeth are much smaller than those of modern apes, but larger and more pointed than those of humans, and shape of the jaw is between the rectangular shape of apes and the parabolic shape of humans. However their pelvis and leg bones far more closely resemble those of modern man, and leave no doubt that they were bipedal (although adapted to walking rather than running (Leakey 1994)). Their bones show that they were physically very strong. Females were substantially smaller than males, a condition known as sexual dimorphism. Height varied between about 107 cm (3'6") and 152 cm (5'0"). The finger and toe bones are curved and proportionally longer than in humans, but the hands are similar to humans in most other details (Johanson and Edey 1981). Most scientists consider this evidence that afarensis was still partially adapted to climbing in trees, others consider it evolutionary baggage.

Kenyanthropus platyops

This species was named in 2001 from a partial skull found in Kenya with an unusual mixture of features (Leakey et al. 2001). It is aged about 3.5 million years old. The size of the skull is similar to A. afarensis and A. africanus, and has a large, flat face and small teeth.

Australopithecus africanus

A. africanus existed between 3 and 2 million years ago. It is similar to afarensis, and was also bipedal, but body size was slightly greater. Brain size may also have been slightly larger, ranging between 420 and 500 cc. This is a little larger than chimp brains (despite a similar body size), but still not advanced in the areas necessary for speech. The back teeth were a little bigger than in afarensis. Although the teeth and jaws of africanus are much larger than those of humans, they are far more similar to human teeth than to those of apes (Johanson and Edey 1981). The shape of the jaw is now fully parabolic, like that of humans, and the size of the canine teeth is further reduced compared to afarensis.

Australopithecus garhi

This species was named in April 1999 (Asfaw et al. 1999). It is known from a partial skull. The skull differs from previous australopithecine species in the combination of its features, notably the extremely large size of its teeth, especially the rear ones, and a primitive skull morphology. Some nearby skeletal remains may belong to the same species. They show a humanlike ratio of the humerus and femur, but an apelike ratio of the lower and upper arm. (Groves 1999; Culotta 1999)

Australopithecus afarensis and africanus, and the other species above, are known as gracile australopithecines, because of their relatively lighter build, especially in the skull and teeth. (Gracile means "slender", and in paleoanthropology is used as an antonym to "robust".) Despite this, they were still more robust than modern humans.

Australopithecus aethiopicus

A. aethiopicus existed between 2.6 and 2.3 million years ago. This species is known from one major specimen, the Black Skull discovered by Alan Walker, and a few other minor specimens which may belong to the same species. It may be an ancestor of robustus and boisei, but it has a baffling mixture of primitive and advanced traits. The brain size is very small, at 410 cc, and parts of the skull, particularly the hind portions, are very primitive, most resembling afarensis. Other characteristics, like the massiveness of the face, jaws and single tooth found, and the largest sagittal crest in any known hominid, are more reminiscent of A. boisei (Leakey and Lewin 1992). (A sagittal crest is a bony ridge on top of the skull to which chewing muscles attach.)

Australopithecus robustus

A. robustus had a body similar to that of africanus, but a larger and more robust skull and teeth. It existed between 2 and 1.5 million years ago. The massive face is flat or dished, with no forehead and large brow ridges. It has relatively small front teeth, but massive grinding teeth in a large lower jaw. Most specimens have sagittal crests. Its diet would have been mostly coarse, tough food that needed a lot of chewing. The average brain size is about 530 cc. Bones excavated with robustus skeletons indicate that they may have been used as digging tools.

Australopithecus boisei (was Zinjanthropus boisei)

A. boisei existed between 2.1 and 1.1 million years ago. It was similar to robustus, but the face and cheek teeth were even more massive, some molars being up to 2 cm across. The brain size is very similar to robustus, about 530 cc. A few experts consider boisei and robustus to be variants of the same species.

Australopithecus aethiopicus, robustus and boisei are known as robust australopithecines, because their skulls in particular are more heavily built. They have never been serious candidates for being direct human ancestors. Many authorities now classify them in the genus Paranthropus.

Homo habilis

H. habilis, "handy man", was so called because of evidence of tools found with its remains. Habilis existed between 2.4 and 1.5 million years ago. It is very similar to australopithecines in many ways. The face is still primitive, but it projects less than in A. africanus. The back teeth are smaller, but still considerably larger than in modern humans. The average brain size, at 650 cc, is considerably larger than in australopithecines. Brain size varies between 500 and 800 cc, overlapping the australopithecines at the low end and H. erectus at the high end. The brain shape is also more humanlike. The bulge of Broca's area, essential for speech, is visible in one habilis brain cast, and indicates it was possibly capable of rudimentary speech. Habilis is thought to have been about 127 cm (5'0") tall, and about 45 kg (100 lb) in weight, although females may have been smaller.

Habilis has been a controversial species. Originally, some scientists did not accept its validity, believing that all habilis specimens should be assigned to either the australopithecines or Homo erectus. H. habilis is now fully accepted as a species, but it is widely thought that the 'habilis' specimens have too wide a range of variation for a single species, and that some of the specimens should be placed in one or more other species. One suggested species which is accepted by many scientists is Homo rudolfensis, which would contain fossils such as ER 1470.

Homo georgicus

This species was named in 2002 to contain fossils found in Dmanisi, Georgia, which seem intermediate between H. habilis and H. erectus. The fossils are about 1.8 million years old, consisting of three partial skulls and three lower jaws. The brain sizes of the skulls vary from 600 to 780 cc. The height, as estimated from a foot bone, would have been about 1.5 m (4'11"). A partial skeleton was also discovered in 2001 but no details are available on it yet. (Vekua et al. 2002, Gabunia et al. 2002)

Homo erectus

H. erectus existed between 1.8 million and 300,000 years ago. Like habilis, the face has protruding jaws with large molars, no chin, thick brow ridges, and a long low skull, with a brain size varying between 750 and 1225 cc. Early erectus specimens average about 900 cc, while late ones have an average of about 1100 cc (Leakey 1994). The skeleton is more robust than those of modern humans, implying greater strength. Body proportions vary; the Turkana Boy is tall and slender (though still extraordinarily strong), like modern humans from the same area, while the few limb bones found of Peking Man indicate a shorter, sturdier build. Study of the Turkana Boy skeleton indicates that erectus may have been more efficient at walking than modern humans, whose skeletons have had to adapt to allow for the birth of larger-brained infants (Willis 1989). Homo habilis and all the australopithecines are found only in Africa, but erectus was wide-ranging, and has been found in Africa, Asia, and Europe. There is evidence that erectus probably used fire, and their stone tools are more sophisticated than those of habilis.

Homo ergaster

Some scientists classify some African erectus specimens as belonging to a separate species, Homo ergaster, which differs from the Asian H. erectus fossils in some details of the skull (e.g. the brow ridges differ in shape, and erectus would have a larger brain size). Under this scheme, H. ergaster would include fossils such as the Turkana boy and ER 3733.

Homo antecessor

Homo antecessor was named in 1977 from fossils found at the Spanish cave site of Atapuerca, dated to at least 780,000 years ago, making them the oldest confirmed European hominids. The mid-facial area of antecessor seems very modern, but other parts of the skull such as the teeth, forehead and browridges are much more primitive. Many scientists are doubtful about the validity of antecessor, partly because its definition is based on a juvenile specimen, and feel it may belong to another species. (Bermudez de Castro et al. 1997; Kunzig 1997, Carbonell et al. 1995)

Homo sapiens (archaic) (also Homo heidelbergensis)

Archaic forms of Homo sapiens first appear about 500,000 years ago. The term covers a diverse group of skulls which have features of both Homo erectus and modern humans. The brain size is larger than erectus and smaller than most modern humans, averaging about 1200 cc, and the skull is more rounded than in erectus. The skeleton and teeth are usually less robust than erectus, but more robust than modern humans. Many still have large brow ridges and receding foreheads and chins. There is no clear dividing line between late erectus and archaic sapiens, and many fossils between 500,000 and 200,000 years ago are difficult to classify as one or the other.

Homo sapiens neanderthalensis (also Homo neanderthalensis)

Neandertal (or Neanderthal) man existed between 230,000 and 30,000 years ago. The average brain size is slightly larger than that of modern humans, about 1450 cc, but this is probably correlated with their greater bulk. The brain case however is longer and lower than that of modern humans, with a marked bulge at the back of the skull. Like erectus, they had a protruding jaw and receding forehead. The chin was usually weak. The midfacial area also protrudes, a feature that is not found in erectus or sapiens and may be an adaptation to cold. There are other minor anatomical differences from modern humans, the most unusual being some peculiarities of the shoulder blade, and of the pubic bone in the pelvis. Neandertals mostly lived in cold climates, and their body proportions are similar to those of modern cold-adapted peoples: short and solid, with short limbs. Men averaged about 168 cm (5'6") in height. Their bones are thick and heavy, and show signs of powerful muscle attachments. Neandertals would have been extraordinarily strong by modern standards, and their skeletons show that they endured brutally hard lives. A large number of tools and weapons have been found, more advanced than those of Homo erectus. Neandertals were formidable hunters, and are the first people known to have buried their dead, with the oldest known burial site being about 100,000 years old. They are found throughout Europe and the Middle East. Western European Neandertals usually have a more robust form, and are sometimes called "classic Neandertals". Neandertals found elsewhere tend to be less excessively robust. (Trinkaus and Shipman 1992; Trinkaus and Howells 1979; Gore 1996)

Homo floresiensis

Homo floresiensis was discovered on the Indonesian island of Flores in 2003. Fossils have been discovered from a number of individuals. The most complete fossil is of an adult female about 1 meter tall with a brain size of 417cc. Other fossils indicate that this was a normal size for floresiensis. It is thought that floresiensis is a dwarf form of Homo erectus - it is not uncommon for dwarf forms of large mammals to evolve on islands. H. floresiensis was fully bipedal, used stone tools and fire, and hunted dwarf elephants also found on the island. (Brown et al. 2004, Morwood et al. 2004, Lahr and Foley 2004)

Homo sapiens sapiens (modern)

Modern forms of Homo sapiens first appear about 195,000 years ago. Modern humans have an average brain size of about 1350 cc. The forehead rises sharply, eyebrow ridges are very small or more usually absent, the chin is prominent, and the skeleton is very gracile. About 40,000 years ago, with the appearance of the Cro-Magnon culture, tool kits started becoming markedly more sophisticated, using a wider variety of raw materials such as bone and antler, and containing new implements for making clothing, engraving and sculpting. Fine artwork, in the form of decorated tools, beads, ivory carvings of humans and animals, clay figurines, musical instruments, and spectacular cave paintings appeared over the next 20,000 years. (Leakey 1994)

Even within the last 100,000 years, the long-term trends towards smaller molars and decreased robustness can be discerned. The face, jaw and teeth of Mesolithic humans (about 10,000 years ago) are about 10% more robust than ours. Upper Paleolithic humans (about 30,000 years ago) are about 20 to 30% more robust than the modern condition in Europe and Asia. These are considered modern humans, although they are sometimes termed "primitive". Interestingly, some modern humans (aboriginal Australians) have tooth sizes more typical of archaic sapiens. The smallest tooth sizes are found in those areas where food-processing techniques have been used for the longest time. This is a probable example of natural selection which has occurred within the last 10,000 years (Brace 1983).

Timeline

This diagram shows roughly the time range in which each hominid species lived:

---

This page is part of the Fossil Hominids FAQ at the talk.origins Archive.

Scientists Discover Why Plague Is So Lethal

ScienceDaily (May 5, 2008) — Bacteria that cause the bubonic plague may be more virulent than their close relatives because of a single genetic mutation, according to research published in the May issue of the journal Microbiology.

"The plague bacterium Yersinia pestis needs calcium in order to grow at body temperature. When there is no calcium available, it produces a large amount of an amino acid called aspartic acid," said Professor Brubaker from the University of Chicago, USA. "We found that this is because Y. pestis is missing an important enzyme."

Bubonic plague has killed over 200 million people during the course of history and is thus the most devastating acute infectious disease known to man. Despite this, we are still uncertain about the molecular basis of its extraordinary virulence.

"Y. pestis evolved from its ancestor Y. pseudotuberculosis within the last 20,000 years, suggesting its high lethality reflects only a few genetic changes. We discovered that a single mutation in the genome of Y. pestis means the enzyme aspartase is not produced," said Professor Brubaker.

Aspartase is present in almost all bacteria but it is curiously absent in many pathogenic types. These include mycobacteria that are pathogenic to man, Francisella tularensis and rickettsiae (both of which cause diseases transmitted to humans via insects). "This suggests that the absence of aspartase may contribute to serious disease," said Professor Brubaker.

Aspartase digests aspartic acid. Because Y. pestis doesn't have the enzyme, it produces much more aspartic acid than is required by the person infected. This may cause an imbalance to the host amino acid pools. "If this is the case then we might be able to reduce the death rates of these diseases by developing a treatment that removes some of the extra aspartic acid," said Professor Brubaker.

---

Adapted from materials provided by Society for General Microbiology, via EurekAlert!, a service of AAAS.

Platypus Genome Explains Animal's Peculiar Features; Holds Clues To Evolution Of Mammals

ScienceDaily (May 7, 2008) — The duck-billed platypus: part bird, part reptile, part mammal — and the genome to prove it.

An international consortium of scientists, led by Washington University School of Medicine in St. Louis, has decoded the genome of the platypus, showing that the animal's peculiar mix of features is reflected in its DNA. An analysis of the genome, published today in the journal Nature, can help scientists piece together a more complete picture of the evolution of all mammals, including humans.

The platypus, classified as a mammal because it produces milk and is covered in a coat of fur, also possesses features of reptiles, birds and their common ancestors, along with some curious attributes of its own. One of only two mammals that lays eggs, the platypus also sports a duck-like bill that holds a sophisticated electrosensory system used to forage for food underwater. Males possess hind leg spurs that can deliver pain-inducing venom to its foes competing for a mate or territory during the breeding season.

"The fascinating mix of features in the platypus genome provides many clues to the function and evolution of all mammalian genomes," says Richard K. Wilson, Ph.D., director of the The Genome Center at Washington University and the paper's senior author. "By comparing the platypus genome to other mammalian genomes, we'll be able to study genes that have been conserved throughout evolution."

The platypus represents the earliest offshoot of the mammalian lineage some 166 million years ago from primitive ancestors that had features of both mammals and reptiles. "What is unique about the platypus is that it has retained a large overlap between two very different classifications, while later mammals lost the features of reptiles," says Wes Warren, Ph.D., an assistant professor of genetics, who led the project.

Comparison of the platypus genome with the DNA of humans and other mammals, which diverged later, and the genomes of birds, whose ancestors branched off an estimated 315 million years ago, can help scientists fill gaps in their understanding of mammalian evolution. The comparison also will allow scientists to date the emergence of genes and traits specific to mammals.

The Nature paper analyzes the genome sequence of a female platypus named Glennie from New South Wales, Australia. The project was largely funded by the National Human Genome Research Institute, part of the National Institutes of Health, and includes scientists from the United States, Australia, England, Germany, Israel, Japan, New Zealand and Spain.

"At first glance, the platypus appears as if it was the result of an evolutionary accident," says Francis S. Collins, M.D., Ph.D., director of NHGRI. "But as weird as this animal looks, its genome sequence is priceless for understanding how mammalian biological processes evolved."

"While we've always been able to compare and consider all of these creatures on the basis of their physical characteristics, internal anatomy and behavior, it's truly amazing to be able to compare their genetic blueprints and begin to get a close-up look at how evolution brings about change," Wilson says.

As part of their analysis, the researchers compared the platypus genome with genomes of the human, mouse, dog, opossum and chicken. They found that the platypus shares 82 percent of its genes with these animals. The chicken genome was chosen because it represents a group of egg-laying animals, including extinct reptiles, which passed on much of their DNA to the platypus and other mammals over the course of evolution.

The researchers also found genes that support egg laying - a feature of reptiles - as well as lactation - a characteristic of all mammals. Interestingly, the platypus lack nipples, so its young nurse through the abdominal skin.

The researchers also attempted to determine which characteristics of the platypus were linked to reptiles at the DNA level. When they analyzed the genetic sequences responsible for venom production in the male platypus, they found it arose from duplications in a group of genes that evolved from ancestral reptile genomes. Amazingly, duplications in the same genes appear to have evolved independently in venomous reptiles.

The platypus swims with its eyes, ears and nostrils closed, relying on electrosensory receptors in its bill to detect faint electric fields emitted by underwater prey. Surprisingly, the researchers found the genome contains an expansion of genes that code for a particular type of odor receptor. "We were expecting very few of these odor receptor genes because the animals spend the majority of their life in the water," Warren says.

Similar genes are found in animals that rely on a sense of smell, such as rodents and dogs, and the scientists suspect that their addition in the platypus allows the animals to detect odors while foraging underwater.

At roughly 2.2 billion base pairs, the platypus genome is about two-thirds the size of the human genome and contains about 18,500 genes, similar to other vertebrates. The animal has 52 chromosomes, including an unusual number of sex chromosomes: 10. The platypus X chromosome bears resemblance to the sex chromosome of a bird, known as Z.

Sequencing and assembling the platypus genome proved far more daunting than sequencing any other mammalian genome to date. About 50 percent of the genome is composed of repetitive elements of DNA, which makes it a challenge to assemble properly.

The platypus genome sequence, along with those for other organisms, such as the mouse, dog, cow, and many other animals can be accessed at GenBank (http://www.ncbi.nih.gov/Genbank) at NIH's National Center for Biotechnology Information.

Warren WC, Mardis ER, Wilson RK, et al. Genome analysis of the platypus reveals unique signatures of evolution. Nature. May 8, 2008.

The platypus genome project was largely funded by the National Human Genome Research Institute.

---

Adapted from materials provided by Washington University School of Medicine.

http://www.sciencedaily.com/images/2008/05/080507131453-large.jpg

Beneficial Mutations

From Talk Origin Archives.

http://www.talkorigins.org/faqs/mutations.html

For a number of reasons it is not simple to give examples of favorable mutations. First of all, as we have seen, traits [6] may be favorable or unfavorable, depending upon the environment. Secondly it is not usually known to what extent a trait is genetically fixed and to what extent it reflects a reaction to the environment. Thirdly we don't usually know what genes effect which traits. Moreover a mutation may be favorable in the sense that it permits survival in an unfavorable environment and yet be unfavorable in a better environment.

However there are a number of good examples:

1. Antibiotic resistance in bacteria

   In modern times antibiotics, drugs that target specific features of bacteria, have become very popular. Bacteria evolve very quickly so it is not surprising that they have evolved resistance to antibiotics. As a general thing this involves changing the features that antibiotics target.

   Commonly, but not always, these mutations decrease the fitness of the bacteria, i.e., in environments where there are not antibiotics present, they don't reproduce as quickly as bacteria without the mutation. This is not always true; some of these mutations do not involve any loss of fitness. What is more, there are often secondary mutations that restore fitness.

   Bacteria are easy to study. This is an advantage in evolutionary studies because we can see evolution happening in the laboratory. There is a standard experiment in which the experimenter begins with a single bacterium and lets it reproduce in a controlled environment. Since bacteria reproduce asexually all of its descendents are clones. Since reproduction is not perfect mutations happen. The experimenter can set the environment so that mutations for a particular attribute are selected. The experimenter knows both that the mutation was not present originally and, hence, when it occurred.

   In the wild it is usually impossible to determine when a mutation occurred. Usually all we know (and often we do not even know that) is the current distribution of particular traits.

   The situation with insects and pesticides is similar to that of bacteria and antibiotics. Pesticides are widely used to kill insects. In turn the insects quickly evolve in ways to become immune to the pesticides.

2. Bacteria that eat nylon

   Well, no, they don't actually eat nylon; they eat short molecules (nylon oligomers) found in the waste waters of plants that produce nylon. They metabolize short nylon oligomers, breaking the nylon linkages with a couple of related enzymes. Since the bonds involved aren't found in natural products, the enzymes must have arisen since the time nylon was invented (around the 1940s). It would appear this happened by new mutations in that time period.

   These enzymes which break down the nylon oligomers appear to have arisen by frameshift mutation from some other gene which codes for a functionally unrelated enzyme. This adaptation has been experimentally duplicated. In the experiments, non-nylon-metabolizing strains of Pseudomonas were grown in media with nylon oligomers available as the primary food source. Within a relatively small number of generations, they developed these enzyme activities. This would appear to be an example of documented occurrence of beneficial mutations in the lab.

3. Sickle cell resistance to malaria

   The sickle cell allele causes the normally round blood cell to have a sickle shape. The effect of this allele depends on whether a person has one or two copies of the allele. It is generally fatal if a person has two copies. If they have one they have sickle shaped blood cells.

   In general this is an undesirable mutation because the sickle cells are less efficient than normal cells. In areas where malaria is prevalent it turns out to be favorable because people with sickle shaped blood cells are less likely to get malaria from mosquitoes.

   This is an example where a mutation decreases the normal efficiency of the body (its fitness in one sense) but none-the-less provides a relative advantage.

4. Lactose tolerance

   Lactose intolerance in adult mammals has a clear evolutionary explanation; the onset of lactose intolerance makes it easy to wean the young. Human beings, however, have taken up the habit of eating milk products. This is not universal; it is something that originated in cultures that kept cattle and goats. In these cultures lactose tolerance had a strong selective value. In the modern world there is a strong correlation between lactose tolerance and having ancestors who lived in cultures that exploited milk as a food.

   It should be understood that it was a matter of chance that the lactose tolerance mutation appeared in a group where it was advantageous. It might have been established first by genetic drift within a group which then discovered that they could use milk. [9]

5. Resistance to atherosclerosis

   Atherosclerosis is principally a disease of the modern age, one produced by modern diets and modern life-styles. There is a community in Italy near Milan (see Appendices II and III for biological details) whose residents don't get atherosclerosis because of a fortunate mutation in one of their forebearers. This mutation is particularly interesting because the person who had the original mutation has been identified.

   Note that this is a mutation that is favorable in modern times because (a) people live longer and (b) people have diets and life-styles that are not like those of our ancestors. In prehistoric times this would not have been a favorable mutation. Even today we cannot be certain that this mutation is reproductively favorable, i.e., that people with this mutation will have more than the average number of descendents. It is clear, however, that the mutation is personally advantageous to the individuals having it.

6. Immunity to HIV

   HIV infects a number of cell types including T-lymphocytes, macrophages, dendritic cells and neurons. AIDS occurs when lymphocytes, particularly CD4+ T cells are killed off, leaving the patient unable to fight off opportunistic infections. The HIV virus has to attach to molecules that are expressed on the surface of the T-cells. One of these molecules is called CD4 (or CD4 receptor); another is C-C chemokine receptor 5, known variously as CCR5, CCCKR5 and CKR5. Some people carry a mutant allele of the CCR5 gene that results in lack of expression of this protein on the surface of T-cells. Homozygous individuals are resistant to HIV infection and AIDS. The frequency of the mutant allele is quite high in some populations that have never been exposed to AIDS so it seems likely that there was prior selection for this allele. (See Appendix IV)

Scientists Report Doubts over Key Theory of Evolutionary Extinction

by Frank Sherwin, M.A.*

Researchers have recently “ruled out a hypothesis” that has been taught as dogma in schools, colleges and universities worldwide: the cause of the Permian extinction, allegedly “the mother of all mass extinctions.”

Geologists and paleontologists state in a recent article in Nature Geoscience that at the end of the Permian era—which they calculate occurred some 250 million years ago—“95 percent of marine species and 70 percent of land species were wiped out.” Called the “Great Dying” by some researchers, it is difficult not to think of a cataclysmic event, such as a global flood (Genesis 6 – 9), when reading of such massive destruction.

Regardless, evolutionary scientists have taught for decades that this Permian extinction event was precipitated by gradual oxygen starvation of the world’s oceans. This supposedly led to a massive die-out of marine life due to “clouds of hydrogen sulphide” rising from the seas.

Now many scientists are stymied as to what caused this devastating event, but Flood geologists have an idea: massive flooding, possible asteroid activity, and large-scale volcanism. History records such a catastrophic event in Genesis 7:11.

Indeed, many scientists are coming closer to the truth when they rule out clouds of hydrogen sulphide and look approvingly at “an impact, or series of impacts, by an asteroid.” Granted, this is not the Flood, but such bombardments probably did occur at this time. In fact, many geologists now agree with creation scientists that earth did experience a worldwide cataclysmic event. Take note of this shift from a position that does not fit the facts to a more reasonable scientific understanding—sudden cataclysm(s) such as asteroids or even a “fierce period of volcanism,” which happens to fit historical accounts found in the biblical record.

Of course, researchers in creation science continue to follow the evidence where it leads, and little by little, Darwinian scientists committed to evolutionary dogma are beginning to confirm what we’ve been stating all along.

Cataract Research: Genetic Defect Responsible For Small Eyes And Clouded Lens Discovered

ScienceDaily (Apr. 10, 2008) — The ocular lens belongs to the optical apparatus and focuses incidental beams of light onto the retina. Now, a research team led by Professor Dr. Jochen Graw of the Institute of Developmental Genetics, of the Helmholtz Zentrum München, has been able to decipher a genetic defect responsible for small eyes and an incomplete, clouded lens in the so-called Aey12 mouse mutants. These results lead to conclusions concerning cataracts in humans, because, in this case too, the lens loses its transparency.

The development of the eye in mammals (and this naturally includes humans) is an extraordinarily complex process beginning in an early embryonic phase. The same applies also to the formation in healthy eyes of elastic and transparent lenses, which focus light beams. With the aid of the ciliary muscles, the lens can change its degree of curvature and thus set itself on varied, far distant objects. As a result, a pin sharp image is created on the retina.
“As with humans, with mice too, the development of the lens starts with the formation of a spherical, hollow sac,” Graw says. “That is the lens vesicle, the cover of which is surrounded by the lens epithelium, composed of a layer of cells. The vesicle is then filled in with fiber cells. In the following course of development, additional fibers originate in the equator of the lens. These scale up the diameter of the lens: a process that lasts a lifetime.”
But not so with the Aey12 mouse mutants, which Graw’s eye researchers in the study group “Molecular Eye Development” have iknvestigated in detail. The animals of this line are distinguished by their unusually small eyes, a microphthalmia. Combined with cataracts, this dosorder is also known in humans and leads nearly always to blindness. With Aey12 mice, the early development of the eye lens is strongly affected. As the scientists in the current issue of the well-known, American journal in the field of ophthalmology, “Investigative Ophthalmology & Visual Sciences”, report, with the mutant mice, the growth of the fibers that fill up the body of the lenses, is completely blocked. “What remains is then a cloudy and functionless small lens sac,” Oliver Puk adds, the first author of the study. “The animals thereby lose their sight almost completely.”

As the scientists in the current study were able to show, the basis of the disease is a defect in a hitherto unknown gene. Genes are units of the hereditary DNA molecule that contains blueprints for proteins. Errors in the sequence of the gene building blocks can lead to proteins with limited or completely lost functions: and in this way, in the worst case, to serious diseases or development disorders. The Neuherberg eye researchers gave the name Gjf1 to the gene responsible for the alterations of the Aey12 mutant mice. It is a member of the Connexin family. “The genes belonging to this group get the information for the construction of channel proteins, which build the cell to cell connections,” Graw declares. “Such channels are of great importance for the interchange between cells: also, among other things, between the fiber cells of the developing eye lens itself.”

The scientists now speculate that through the newly discovered mutation, the structure of the Gjf1 channel protein is changed, and in this way the formation of the channel is hindered. But through this, the communication between the developing lens fibers would break down. Thus, it would be conceivable that signal molecules essential for the development of the lens are no longer exchanged, or only to a limited extent. In this scenario, faulty cell communication would be the cause of the development of the fibers stopping: and ultimately, of the cloudiness of the eye lens, which would otherwise be transparent.

This very phenomenon is also observed in cataracts in humans, a common disease, which appears mostly in the elderly: in Germany alone more than half a million operations are carried out annually, in which the cloudy and opaque lens is replaced with an implant. “Our results will surely also provide an insight into the origin of cataracts,” Graw adds. “Moreover, so far, there has not yet been any mutation in humans equivalent to Gjf1 gene of mice. But this will now change soon, for sure.”

Journal reference: Oliver Puk, Jana Löster, Claudia Dalke, Dian Soewarto, Helmut Fuchs, Birgit Budde, Peter Nürnberg, Eckhard Wolf, Martin Hrabé de Angelis, and Jochen Graw (2008): Mutation in a Novel Connexin-like Gene (GJF1) in the Mouse Affects Early Lens Development and Causes a Variable Small-Eye Phenotype. Investigative Ophthalmology & Visual Science, vol 49, pp 1525-1532

Adapted from materials provided by Helmholtz Zentrum München - German Research Center for Environmental Health.

Skulls Of Modern Humans And Ancient Neanderthals Evolved Differently Because Of Chance, Not Natural Selection

ScienceDaily (Mar. 20, 2008) — New research led by UC Davis anthropologist Tim Weaver adds to the evidence that chance, rather than natural selection, best explains why the skulls of modern humans and ancient Neanderthals evolved differently. The findings may alter how anthropologists think about human evolution.

Weaver's study appears in the March 17 issue of the Proceedings of the National Academy of Sciences. It builds on findings from a study he and his colleagues published last year in the Journal of Human Evolution, in which the team compared cranial measurements of 2,524 modern human skulls and 20 Neanderthal specimens. The researchers concluded that random genetic change, or genetic drift, most likely account for the cranial differences.
In their new study, Weaver and his colleagues crunched their fossil data using sophisticated mathematical models -- and calculated that Neanderthals and modern humans split about 370,000 years ago. The estimate is very close to estimates derived by other researchers who have dated the split based on clues from ancient Neanderthal and modern-day human DNA sequences.
The close correlation of the two estimates -- one based on studying bones, one based on studying genes -- demonstrates that the fossil record and analyses of DNA sequences give a consistent picture of human evolution during this time period.
"A take-home message may be that we should reconsider the idea that all morphological (physical) changes are due to natural selection, and instead consider that some of them may be due to genetic drift," Weaver said. "This may have interesting implications for our understanding of human evolution."
Weaver conducted the research with Charles Roseman, an anthropologist at the University of Illinois at Urbana-Champaign, and Chris Stringer, a paleontologist at the Natural History Museum in London.
Adapted from materials provided by University of California, Davis.

Fossil From Last Common Ancestor Of Neanderthals And Humans Found In Europe, 1.2 Million Years Old

ScienceDaily (Apr. 4, 2008) — University of Michigan researcher Josep M. Pares is part of a team that has discovered the oldest known remains of human ancestors in Western Europe.
The find shows that members of the genus Homo, to which modern humans belong, colonized the region much earlier than previously believed. Details of the discovery were published in the March 27 issue of the journal Nature.
The fossil—a small piece of jawbone with a few teeth—was found last year in a cave in the mountains of northern Spain, along with primitive stone tools and bones of animals that appear to have been butchered.
The team, led by Spanish researchers Juan Luis Arsuaga, José María Bermúdez de Castro and Eudald Carbonell, used three separate techniques (including paleomagnetic analyses performed by Pares) to determine that the fossil is about 1.2 million years old. That's 500,000 years older than the previous oldest known humanlike fossils from the area. The new find bolsters the view that Homo reached Europe not long after leaving Africa almost 2 million years ago.
"It seems probable that the first European population came from the region of the Near East, the true crossroads between Africa and Eurasia, and that it was related to the first demographic expansion out of Africa," said Pares, who is a research scientist in the U-M Department of Geological Sciences and program director of the newly created National Research Center on Human Evolution (CENIEH) in Burgos, Spain, with which most of the authors are affiliated.
The researchers tentatively classified the new fossil as an earlier example Homo antecessor (Pioneer Man), the species represented by the previous oldest fossils and thought to be the last common ancestor of Neanderthals and modern humans.
"This is a very significant advance toward a better understanding of the nature, age and protagonists of the first European human settlement," Pares said.
Adapted from materials provided by University of Michigan.

The Theory of Evolution

This theory really fascinate me! Why? It has been a very controversial subject ever since Charles Darwin proposed it to the Science World.

Are we really descent from lowly creature that evolved millions of years ago? Are we created by supernatural forces a few thousand years ago?

What is exactly a Theory of Evolution?
Darwin defined this term as "descent with modification." It is the change in a lineage of populations between generations. In general terms, biological evolution is the process of change by which new species develop from preexisting species over time; in genetic terms, evolution can be defined as any change in the frequency of alleles in populations of organisms from generation to generation.

When we talk about evolution there are two things that we should consider seriously; Natural Selection and Mutation.

Natural selection: The differential survival and reproduction of classes of organisms that differ from one another in one or more usually heritable characteristics. Through this process, the forms of organisms in a population that are best adapted to their local environment increase in frequency relative to less well-adapted forms over a number of generations. This difference in survival and reproduction is not due to chance.

Mutations: Changes in the genome (genetic constitution). There are quite a number of ways in which mutations can happen. They also differ in the way that they impact evolution.

Mutations which occur when the genome is copied during reproduction are known as vertical transfer mutations. They are called vertical transfer mutations because they are transferred from ancestor to descendent along vertical lines of descent. In the original work on population genetics it was assumed that all mutations were vertical transfer mutations.

Horizontal transfer mutations occur when DNA is moved from one organism to another. Horizontal transfer can be a major source of evolutionary novelty. It is important because new genes can be propagated much more rapidly by horizontal transfer than by vertical transfer. If evolution is depicted by the tree, vertical genetic movement is the transmission of genes down branches; horizontal genetic movement is the transmission of genes between the branches.
Intra-organism transfer mutations occur when genes or parts of genes move around within an organism.

Strictly speaking, hybrids (mating across species) are not mutants. In many groups of species, particularly among plants, genes are transferred from to one species to another via hybrids.

Types of mutations:

1. Point mutations
   The most common type of copying error is the point mutation. In this form of mutation the nucleotide at a site is replaced by a different nucleotide. When people talk about mutation rates they are usually talking about rates of point mutations.
   Effects of point mutations: Point mutations in junk DNA are common but have no effect. Sometimes point mutations in regulatory regions have no effect and sometimes they alter the expression of some genes.


2. Additions and deletions
   During copying a segment of DNA may be deleted or a new segment may be inserted. Typically this happens as a result of chromosome breakage or realignment. (See below.) Additions and deletions can also be produced by certain types of horizontal transfer.
   Effects of additions and deletions: If the length of the new or deleted segment is not a multiple of three the translation will be garbled after the point at which the insertion/deletion occurred because the frame reading is now misaligned. This is known as a frameshift mutation. In some genes there are segments that may be duplicated as a block. This is known as tandem duplication.


3. Chromosomal duplication
   Sometimes one or more chromosomes are duplicated during reproduction; the offspring get extra copies of those chromosomes.
   Effects of chromosomal duplication: Duplicating only one chromosome is generally disadvantageous; an example in human beings is Down's syndrome. Having multiple copies of all of the chromosomes is known as polyploidy. Polyploidy is rare in fungi and animals (although it does occur) and is common in plants. It has been estimated that 20-50% of all plant species arise as the result of polyploidy.
   Gene duplication is very common; it is important because it provides a way to evolve new capabilities while retaining the old capabilities. All intermediate stages can be found in nature, from a single gene with alternate alleles to nearly identical duplicated genes with slightly different functional alleles to gene families of evolutionarily related genes with different functionalities.


4. Chromosomal breakage and realignment
   During reproduction a chromosome may break into two pieces or two chromosomes may be joined together. A section may be moved from one part of the chromosome to another or may be flipped in orientation (inverted). This is the mechanism by which deletions, duplications and transpositions my occur.
   Effects of chromosomal breakage and realignment: Quite often these types of changes do not affect the viability of the organism (the genes are still there; they're just in different places) but, in sexually reproducing species, they may make it less likely for the organism to produce viable, fertile offspring.


5. Retroviruses
   Certain viruses have the ability to insert a copy of themselves into the genome of a host. The chemical that make this possible (reverse transcriptase) is widely used in genetic engineering.
   Effects of retroviruses: Usually this is a way for the virus to get the host to do the work of reproducing the virus. Sometimes, however, the inserted gene mutates and becomes a permanent part of the host organism's genome. Depending on the position of the viral DNA in the host genome, genes may be disrupted or their expression altered. When insertions occur in the germline of multicellular organisms, they can be passed on vertically.


6. Plasmids
   Plasmids are little pieces of circular DNA that are passed from bacterium to bacterium. Plasmids can be transferred across species lines.
   Effects of plasmid transfer: Plasmid transfer is an important way of spreading useful genes such as those which confer resistance to antibiotics. Plasmid transfer is an example of horizontal transfer.


7. Bacterial DNA exchange
   Bacteria can exchange DNA directly. They often do this in response to environmental stress.
   Effects of bacterial DNA exchange: Exchange is often fatal to one or both of the bacteria involved. Sometimes, however, one or both of the partners acquires genes which are essential for the current environment.


8. Higher level transfer
   Some parasites can pick up genetic material from one organism and carry it to the next. This has been observed in fruit flies in the wild.
   Effects of higher level transfer: When this happens novel alleles can spread much more rapidly through a species than they would for ordinary gene flow.


9. Symbiotic transfer
   When two organisms exist in a close symbiotic relationship one may "steal" genes from the other. The most notable example of this are mitochondria. In most organisms with mitochondria most of the original mitochondrial genes have moved from the mitochondria to the nuclear genome.
   Effects of symbiotic transfer: A major effect is that the symbiotic relationship changes from being optional to be obligatory.


10. Transposons
    Transposons are genes that can move from one place in the genome to another.
    Effects of transposons: Depending on the position of insertion, transposons can disrupt or alter the expression of host genes. In some species most mutations due to transposon insertion. For example, in Drosophila, 50-85% of mutations are due to transposon insertions.

In The Theory of Evolution, the mutation that suppose to have occurred are the beneficial or favorable mutation that are hereditary and together with forces of natural selection, our world is full of diverse and complex fauna and flora that evolved from simple common ancestor.

Welcome

Everybody!Welcome to my blog site of the Cyberworld!