Simpler Times: Did an Earlier Genetic Molecule Predate DNA and RNA?

ScienceDaily (Jan. 9, 2012) — In the chemistry of the living world, a pair of nucleic acids -- DNA and RNA -- reign supreme. As carrier molecules of the genetic code, they provide all organisms with a mechanism for faithfully reproducing themselves as well as generating the myriad proteins vital to living systems.

Yet according to John Chaput, a researcher at the Center for Evolutionary Medicine and Informatics, at Arizona State University's Biodesign Institute^®, it may not always have been so.

Chaput and other researchers studying the first tentative flickering of life on earth have investigated various alternatives to familiar genetic molecules. These chemical candidates are attractive to those seeking to unlock the still-elusive secret of how the first life began, as primitive molecular forms may have more readily emerged during the planet's prebiotic era.

One approach to identifying molecules that may have acted as genetic precursors to RNA and DNA is to examine other nucleic acids that differ slightly in their chemical composition, yet still possess critical properties of self-assembly and replication as well as the ability to fold into shapes useful for biological function.

According to Chaput, one interesting contender for the role of early genetic carrier is a molecule known as TNA, whose arrival on the primordial scene may have predated its more familiar kin. A nucleic acid similar in form to both DNA and RNA, TNA differs in the sugar component of its structure, using threose rather than deoxyribose (as in DNA) or ribose (as in RNA) to compose its backbone.

In an article released online January 9 in the journal Nature Chemistry, Chaput and his group describe the Darwinian evolution of functional TNA molecules from a large pool of random sequences. This is the first case where such methods have been applied to molecules other than DNA and RNA, or very close structural analogues thereof. Chaput says "the most important finding to come from this work is that TNA can fold into complex shapes that can bind to a desired target with high affinity and specificity." This feature suggests that in the future it may be possible to evolve TNA enzymes with functions required to sustain early life forms.

Nearly every organism on earth uses DNA to encode chunks of genetic information in genes, which are then copied into RNA. With the aid of specialized enzymes known as polymerases, RNA assembles amino acids to form essential proteins. Remarkably, the basic functioning of the genetic code remains the same, whether the organism is a snail or a senator, pointing to a common ancestor in the DNA-based microbial life already flourishing some 3.5 billion years ago.

Nevertheless, such ancestors were by this time quite complex, leading some scientists to speculate about still earlier forms of self-replication. Before DNA emerged to play its dominant role as the design blueprint for life, a simpler genetic world dominated by RNA may have prevailed. The RNA world hypothesis as it's known alleges that ribonucleic acid (RNA) acted to store genetic information and catalyze chemical reactions much like a protein enzyme, in an epoch before DNA, RNA and proteins formed the integrated system prevalent today throughout the living world.

While the iconic double helix of DNA is formed from two complimentary strands of nucleotides, attached to each other by base pairing in a helical staircase, RNA is single-stranded. The two nucleic acids DNA and RNA are named for the type of sugar complex that forms each molecule's sugar-phosphate backbone -- a kind of molecular thread holding the nucleotide beads together.

Could a simpler, self-replicating molecule have existed as a precursor to RNA, perhaps providing genetic material for earth's earliest organisms? Chaput's experiments with the nucleic acid TNA provide an attractive case. To begin with, TNA uses tetrose sugars, named for the four-carbon ring portion of their structure. They are simpler than the five-carbon pentose sugars found in both DNA and RNA and could assemble more easily in a prebiotic world, from two identical two-carbon fragments.

This advantage in structural simplicity was originally thought to be an Achilles' heel for TNA, making its binding behavior incompatible with DNA and RNA. Surprisingly, however, research has now shown that a single strand of TNA can indeed bind with both DNA and RNA by Watson-Crick base pairing -- a fact of critical importance if TNA truly existed as a transitional molecule capable of sharing information with more familiar nucleic acids that would eventually come to dominate life.

In the current study, Chaput and his group use an approach known as molecular evolution to explore TNA's potential as a genetic biomolecule. Such work draws on the startling realization that fundamental Darwinian properties -- self-replication, mutation and selection -- can operate on non-living chemicals.

Extending this technique to TNA requires polymerase enzymes that are capable of translating a library of random DNA sequences into TNA. Once such a pool of TNA strands has been generated, a process of selection must successfully identify members that can perform a given function, excluding the rest. As a test case, the team hoped to produce through molecular evolution, a TNA strand capable of acting as a high-specificity, high-affinity binding receptor for the human protein thrombin.

They first attempted to demonstrate that TNA nucleotides could attach by complementary base pairing to a random sequence of DNA, forming a hybrid DNA-TNA strand. A DNA polymerase enzyme assisted the process. Many of the random sequences, however, contained repeated sections of the guanine nucleotide, which had the effect of pausing the transcription of DNA into TNA. Once random DNA libraries were built excluding guanine, a high yield of DNA-TNA hybrid strands was produced.

The sequences obtained were 70 nucleotides in length, long enough Chaput says, to permit them to fold into shapes with defined binding sites. The DNA-TNA hybrids were then incubated with the target molecule thrombin. Sequences that bound with the target were recovered and amplified through PCR. The DNA portion was removed and used as a template for further amplification, while the TNA molecules displaying high-affinity, high specificity binding properties were retained.

Additionally, the binding affinity of the evolved and selected TNA molecules was tested against two other common proteins, for which they displayed no affinity, strengthening the case that a highly specific binding molecule had resulted from the group's directed evolution procedure.

Chaput suggests that issues concerning the prebiotic synthesis of ribose sugars and the non-enzymatic replication of RNA may provide circumstantial evidence of an earlier genetic system more readily produced under primitive earth conditions. Although solid proof that TNA acted as an RNA precursor in the prebiotic world may be tricky to obtain, Chaput points to the allure of this molecule as a strong candidate, capable of storing information, undergoing selection processes and folding into tertiary structures that can perform complex functions. This result provides the motivation to explore TNA as an early genetic system.

Chaput is optimistic that major questions about the prebiotic synthesis of TNA, its role in the origin and early evolution of life on earth, and eventual genetic takeover by RNA will, over time, be answered.

http://www.sciencedaily.com/releases/2012/01/120109103029.htm

Most Recent European Great Ape Discovered

ScienceDaily (Jan. 13, 2012) — Based on a hominid molar, scientists from Germany, Bulgaria and France have documented that great apes survived in Europe in savannah-like landscapes until seven million years ago.

A seven million year old pre-molar of a hominid discovered near the Bulgarian town of Chirpan documents that great apes survived longer in Europe than previously believed. An international team of scientists from the Bulgarian Academy of Science, the French Centre National de la Recherche Scientifique, and Madelaine Böhme from the Senckenberg Center for Human Evolution and Paleoenvironment at the University of Tübingen was involved in the project. The new discovery may cause a revision in our understanding of some major steps in hominid evolution.

To date scientists have assumed that great apes went extinct in Europe at least 9 million years ago because of changing climatic and environmental conditions. Under the direction of Nikolai Spassov from the National Museum of Natural Science in Sofia, Bulgaria, the molar was discovered in Upper Miocene fluvial sediments near Chirpan. The morphology and the great thickness of the tooth enamel point to a hominid fossil. The age of the fossiliferous sands at 7 million years reveals the fossil to be most recent known great ape from continental Europe.

Until now, the most recent fossil was that of a 9.2 million year old specimen of Ouranopithecus macedonensis from Greece. Hominids therefore were thought to have disappeared from Europe prior to 9 million years ago. At this time, European terrestrial ecosystems had been changed from mostly evergreen and lush forests to savannah-like landscapes with a seasonal climate. It had been thought that great apes, which typically consume fruits, were unable to survive this change due to a seasonal deficiency of fruits.

The scientists found animals typical of a savannah in the fossil-bearing layer: several species of elephants, giraffes, gazelles, antelopes, rhinos, and saber-toothed cats. This discovery suggests that European hominids were able to adapt to the seasonal climate of a savannah-like ecosystem. This conclusion is further corroborated by electron microscope analysis of the tooth's masticatory surface, which reveals that the Bulgarian hominid had consumed hard and abrasive objects like grass, seeds, and nuts. In this respect, the feeding behavior of this animal resembles that of later African hominids from about 4 million years ago (e.g. australopithecids like 'Lucy').

„We now also need to rethink where the origin of humans took place," says Professor Madelaine Böhme of the University of Tübingen. So far, most scientists believe that human evolution happened exclusively in Africa and that humans migrated from Africa to other continents. "There is increasing evidence, however, that a significant part of human evolution happened outside Africa, in Europe and western Asia."

That migration plays a major role in early hominid evolution was documented by paleontologists from the Senckenberg Center for Human Evolution and Paleoenvironment in June 2011, when they presented an early Eurasian hominid. A further piece to the puzzle had furthermore been an isolated molar tooth excavated southwest of Sigmaringen, Germany, and dated to 17 million years ago. The Tübingen group of paleoclimatologists led by Böhme reconstructed the climate at this time and demonstrated that great apes dispersed at this time under a tropical-subtropical and humid climate from Africa into Europe. Together, both investigations document an at least 10 million year lasting population of great apes in Europe and a significant evolution from fruit-eaters to harder object feeders.

http://www.sciencedaily.com/releases/2012/01/120113210347.htm

Evolution Is Written All Over Your Face

ScienceDaily (Jan. 11, 2012) — Why are the faces of primates so dramatically different from one another?

UCLA biologists working as "evolutionary detectives" studied the faces of 129 adult male primates from Central and South America, and they offer some answers in research published Jan. 11, in the early online edition of the journal Proceedings of the Royal Society B. The faces they studied evolved over at least 24 million years, they report.

"If you look at New World primates, you're immediately struck by the rich diversity of faces," said Michael Alfaro, a UCLA associate professor of ecology and evolutionary biology and the senior author of the study. "You see bright red faces, moustaches, hair tufts and much more. There are unanswered questions about how faces evolve and what factors explain the evolution of facial features. We're very visually oriented, and we get a lot of information from the face."

Some of theprimate species studied are solitary, while others live in groups that can include dozens or even hundreds of others.

The life scientists divided each face into 14 regions; coded the color of each part, including the hair and skin; studied the patterns and anatomy of the faces; and gave each a "facial complexity" score. They studied how the complexity of primate faces evolved over time and examined the primates' social systems. To assess how facial colors are related to physical environments, they analyzed environmental variables, using the longitude and latitude of primates' habitats as a proxy for sun exposure and temperature. They also used statistical methods to analyze the evolutionary history of the primate groups and when they diverged from one another.

"We found very strong support for the idea that as species live in larger groups, their faces become more simple, more plain," said lead author Sharlene Santana, a UCLA postdoctoral scholar in ecology and evolutionary biology and a postdoctoral fellow with UCLA's Institute for Society and Genetics. "We think that is related to their ability to communicate using facial expressions. A face that is more plain could allow the primate to convey expressions more easily.

"Humans have pretty bare faces, which may allow us to see facial expressions more easily than if, for example, we had many colors in our faces."

The researchers' finding that faces are more simple in larger groups came as a surprise.

"Initially, we thought it might be the opposite," Santana said. "You might expect that in larger groups, faces would vary more and have more complex parts that would allow one individual to identify any member of that group. That is not what we found. Species that live in larger groups live in closer proximity to one another and tend to use facial expressions more than species in smaller groups that are more spread out. Being in closer proximity puts a stronger pressure on using facial expressions."

"This finding suggests that facial expressions are increasingly important in large groups," said co-author Jessica Lynch Alfaro, associate director of the UCLA Institute for Society and Genetics. "If you're highly social, then facial expressions matter more than having a highly complex pattern on your face. "

The evolutionary biologists also found that when primates live in environment with more species that are closely related, their faces are more complex, regardless of their group size. This finding is consistent with their need to recognize individuals of other closely related species that live in the same habitat to avoid interbreeding, Santana said.

Santana, Lynch Alfaro and Alfaro present the first quantitative evidence linking social behavior to the evolution of facial diversity and complexity in primates, and they also show that ecology controls aspects of facial patterns.

As species live closer to the equator, the skin and hair around their eyes get darker, the biologists report. They also found that regions of the face around the nose and mouth get darker when species live in humid environments and denser forests and that facial hair gets longer as species live farther from the equator and the climate gets colder, which may be related to regulating body temperature.

"This is a good start toward understanding facial diversity," Alfaro said. "There was not a good idea before about what aspects of faces were shaped by which evolutionary pressure. Sharlene [Santana] has been able to say what social complexity, social behavior and ecology are doing to faces."

In the future, Santana, Lynch Alfaro and Alfaro may use computer facial-recognition software to help quantify the faces in a more sophisticated way. They also plan to study the faces of carnivores, including big cats.

Previous studies, they noted, have found that primate species with moustaches and beards (such as No. 11 and No. 9 in the accompanying image) tend to look poker-faced; they don't move their faces much when they communicate, compared with other species (such as No. 4).

Alfaro praised Santana's ability to answer some of these difficult evolutionary questions.

"Sharlene has tested ideas that have been virtually impossible to test before," he said. "She has found a clever way to implicate the degree of sociality as contributing to the diversity of faces. Social behavior explains some aspects of facial diversity."

Santana also devised a way to test a theory that has been in the biological literature for decades but had never been tested before. As a lineage diverges and species accumulate, a series of changes in facial coloration and body coloration emerges. The theory she was able to test suggests that once a species evolves to have a certain color, such as hair color, the change is irreversible and it cannot evolve back to a previous color in its lineage. Santana found this theory to be wrong.

"The idea in biology that evolutionary change is irreversible is rejected very strongly by our data," Alfaro said.

Lessons for human faces?

Does the study have implications for the evolution of human faces?

The findings do suggest, Alfaro said, that an important factor in shaping human faces is the premium on making unambiguous facial expressions.

"Humans don't have all these elaborate facial ornamentations, but we do have the ability to communicate visually with facial expressions," Alfaro said. "Does reduced coloration complexity create a blank palate for visual expressions that can be conveyed more easily? That is an idea we are testing."

Santana's research is funded by fellowships from the National Science Foundation and UCLA's Institute for Society and Genetics.

http://www.sciencedaily.com/releases/2012/01/120111223744.htm

Bacteria's Move from Sea to Land May Have Occurred Much Later Than Thought

ScienceDaily (Dec. 22, 2011) — Research by University of Tennessee, Knoxville, faculty has discovered that bacteria's move from sea to land may have occurred much later than thought. It also has revealed that the bacteria may be especially useful in bioenergy research.

Igor Jouline, UT-Oak Ridge National Laboratory joint faculty professor of microbiology and researcher at ORNL's Joint Institute for Computational Sciences, performed a genome sequence analysis of the soil bacteria Azospirillum, a species' whose forebearers made the sea-to-land move. The analysis indicates the shift may have occurred only 400 million years ago, rather than approximately two billion years earlier, as originally thought.

Published in the journal PLoS Genetics, Jouline calculated the timing of the sea-land transition through studies of genome sequences of two species of Azospirillum, a terrestrial genus with almost exclusively aquatic relatives.

Jouline conducted his research with Kristin Wuichet and Leonid Sukharnikov of the Department of Microbiology, Gladys Alexandre of Department of Biochemistry, Cellular, and Molecular Biology, and Kirill Borziak, a graduate student in the ORNL-UT Genome Science and Technology program.

"In the absence of fossil records for bacteria, it is hard to estimate when and how bacteria transitioned from sea to land," said Jouline. "Using genome sequencing and analysis of bacteria of the genus Azospirillum, which colonizes roots of important cereals and grasses, we show that these organisms transitioned from aquatic environments to land approximately at the same time that plants appeared on land -- 400 million years ago."

Jouline said the Azospirillum lineage the team studied has obtained nearly half of its genome from terrestrial organisms, which suggests the much later water-land transition, which coincides with the first appearance of plants on land.

The study is of interest to researchers beyond its evolutionary significance. Azospirillum is currently used as a biofertilizer for grasses and some other plants. Commercial fertilizers containing the bacteria are available world wide.

"Because these bacteria colonize roots of grasses and improve their growth and development, they might be important for bioenergy research," Jouline said.

"Switchgrass is one of the most important potential sources of bioethanol. In this study, we have shown that genomes of Azospirillum contain as many cellulolytic enzymes as those from known effective cellulose degrading bacteria," he said. "We have also demonstrated experimentally that azospirilla do degrade cellulose, especially the strain that can penetrate grass roots."

The team also included Greg Hurst of the ORNL Chemical Sciences Division; research groups from Pasteur Institute in Paris, France, universities of Lyon and Toulouse in France, University of Sydney in Australia, and the National University of Mexico; and Florence Wisniewski-Dye from the University of Lyon.

The research was supported with funding from the National Science Foundation and the Department of Energy's Office of Science.

http://www.sciencedaily.com/releases/2011/12/111222195017.htm

Molecular 'Culprit' in Rise of Planetary Oxygen

ScienceDaily (Jan. 10, 2012) — A turning point in the history of life occurred 2 billion to 3 billion years ago with the unprecedented appearance and dramatic rise of molecular oxygen. Now researchers report they have identified an enzyme that was the first -- or among the first -- to generate molecular oxygen on Earth.

The new findings, reported in the journal Structure, build on more than a dozen previous studies that aim to track the molecular evolution of life by looking for evidence of that history in present-day protein structures. These studies, led by University of Illinois crop sciences and Institute for Genomic Biology professor Gustavo Caetano-Anollés, focus on structurally and functionally distinct regions of proteins -- called folds -- that are part of the universal toolkit of living cells.

Protein folds are much more stable than the sequences of amino acids that compose them, Caetano-Anollés said. Mutations or other changes in sequence often occur without disrupting fold structure or function. This makes folds much more reliable markers of long-term evolutionary patterns, he said.

In the new study, Caetano-Anollés, working with colleagues in China and Korea, tackled an ancient mystery: Why did some of the earliest organisms begin to generate oxygen, and why?

"There is a consensus from earth scientists that about 2.4 billion years ago there was a big spike in oxygen on Earth," Caetano-Anollés said. They generally agree that this rise in oxygen, called the Great Oxygenation Event, was tied to the emergence of photosynthetic organisms.

"But the problem now comes with the following question," he said. "Oxygen is toxic, so why would a living organism generate oxygen? Something must have triggered this."

The researchers looked for answers in the "molecular fossils" that still reside in living cells. They analyzed protein folds in nearly a thousand organisms representing every domain of life to assemble a timeline of protein history. Their timeline for this study was limited to single-fold proteins (which the researchers believe are the most ancient), and was calibrated using microbial fossils that appeared in the geologic record at specific dates.

The analysis revealed that the most ancient reaction of aerobic metabolism involved synthesis of pyridoxal (the active form of vitamin B6, which is essential to the activity of many protein enzymes) and occurred about 2.9 billion years ago. An oxygen-generating enzyme, manganese catalase, appeared at the same time.

Other recent studies also suggest that aerobic (oxygen-based) respiration began on Earth 300 to 400 million years before the Great Oxidation Event, Caetano-Anollés said. This would make sense, since oxygen production was probably going on for a while before the spike in oxygen occurred.

Catalases convert hydrogen peroxide to water and oxygen. The researchers hypothesize that primordial organisms "discovered" this enzyme when trying to cope with an abundance of hydrogen peroxide in the environment. Some geochemists believe that hydrogen peroxide was abundant at this time as a result of intensive solar radiation on glaciers that covered much of Earth.

"In the glacial melt waters you would have a high concentration of hydrogen peroxide and that would be gradually exposing a number of the primitive organisms (alive at that time)," Caetano-Anollés said. The appearance of manganese catalase, an enzyme that degrades hydrogen peroxide and generates oxygen as a byproduct, makes it a likely "molecular culprit for the rise of oxygen on the planet," he said.

The research team included scientists from the Korea Research Institute of Bioscience and Biotechnology; Huazhong Agricultural University, China; and Shandong University of Technology, China.

http://www.sciencedaily.com/releases/2012/01/120110140216.htm

Death Anxiety Prompts People to Believe in Intelligent Design, Reject Evolution, Study Suggests

ScienceDaily (Mar. 30, 2011) — Researchers at the University of British Columbia and Union College (Schenectady, N.Y.) have found that people's death anxiety can influence them to support theories of intelligent design and reject evolutionary theory.

Existential anxiety also prompted people to report increased liking for Michael Behe, intelligent design's main proponent, and increased disliking for evolutionary biologist Richard Dawkins.

The lead author is UBC Psychology Asst. Prof. Jessica Tracy with co-authors Joshua Hart, assistant professor of psychology at Union College, and UBC psychology PhD student Jason Martens.

Published in the March 30 issue of the journal PLoS ONE, their paper is the first to examine the implicit psychological motives that underpin one of the most heated debates in North America. Despite scientific consensus that intelligent design theory is inherently unscientific, 25 per cent of high school biology teachers in the U.S. devote at least some class time to the topic of intelligent design. And in Canada, for example, Alberta passed a law in 2009 that may allow parents to remove children from courses covering evolution.

British evolutionary biologist Prof. Dawkins, like the majority of scientists, argues that life's origins are best explained by Charles Darwin's theory of natural selection. However, intelligent design advocates such as Prof. Behe, a U.S. author and biochemist, assert that complex biochemical and cellular structures are too complex to be explained by evolutionary mechanisms and should be attributed to a supernatural creator.

"Our results suggest that when confronted with existential concerns, people respond by searching for a sense of meaning and purpose in life," says Tracy. "For many, it appears that evolutionary theory doesn't offer enough of a compelling answer to deal with these big questions."

The researchers carried out five studies with 1,674 U.S. and Canadian participants of different ages and a broad range of educational, socioeconomic and religious backgrounds.

In each study, participants were asked to imagine their own death and write about their subsequent thoughts and feelings, or they were assigned to a control condition: imagining dental pain and writing about that.

The participants were then asked to read two similarly styled, 174-word excerpts from the writings of Behe and Dawkins, which make no mention of religion or belief, but describe the scientific and empirical support for their respective positions.

After going through these steps, participants who imagined their own death showed greater support for intelligent design and greater liking for Behe, or a rejection of evolution theory coupled with disliking for Dawkins, compared to participants in the control condition.

However, the research team saw reversed effects during the fourth study which had a new condition. Along with writings by Behe and Dawkins, there was an additional passage by Carl Sagan. A cosmologist and science writer, Sagan argues that naturalism -- the scientific approach that underlies evolution, but not intelligent design -- can also provide a sense of meaning. In response, these participants showed reduced belief in intelligent design after being reminded of their own mortality.

Tracy says, "These findings suggest that individuals can come to see evolution as a meaningful solution to existential concerns, but may need to be explicitly taught that taking a naturalistic approach to understanding life can be highly meaningful."

Similar results emerged in the fifth study, carried out entirely with natural science students at graduate and undergraduate levels. After thinking about death, these participants also showed greater support for the theory of evolution and liking of Dawkins, compared to control participants.

The researchers say these findings indicate a possible means of encouraging students to accept evolution and reject intelligent design.

"Natural science students have been taught to view evolutionary theory as compatible with the desire to find a greater sense of meaning in life," says Tracy. "Presumably, they already attain a sense of existential meaning from evolution."

The study received support from the Social Science and Humanities Research Council of Canada and the Michael Smith Foundation for Health Research.

http://www.sciencedaily.com/releases/2011/03/110330192201.htm

Evolution: Not Only the Fittest Survive

ScienceDaily (Mar. 29, 2011) — Darwin's notion that only the fittest survive has been called into question by new research published in the journal Nature. A collaboration between the Universities of Exeter and Bath in the UK, with a group from San Diego State University in the US, challenges our current understanding of evolution by showing that biodiversity may evolve where previously thought impossible.


Bacteria growing on a Petri plate. (Credit: iStockphoto/Monika Wisniewska)

The work represents a new approach to studying evolution that may eventually lead to a better understanding of the diversity of bacteria that cause human diseases.

Conventional wisdom has it that for any given niche there should be a best species, the fittest, that will eventually dominate to exclude all others.

This is the principle of survival of the fittest. Ecologists often call this idea the `competitive exclusion principle' and it predicts that complex environments are needed to support complex, diverse populations.

Professor Robert Beardmore, from the University of Exeter, said: "Microbiologists have tested this principle by constructing very simple environments in the lab to see what happens after hundreds of generations of bacterial evolution, about 3,000 years in human terms. It had been believed that the genome of only the fittest bacteria would be left, but that wasn't their finding. The experiments generated lots of unexpected genetic diversity."

This test tube biodiversity proved controversial when first observed and had been explained away with claims that insufficient time had been allowed to pass for a clear winner to emerge.

The new research shows the experiments were not anomalies.

Professor Laurence Hurst, of the University of Bath, said: "Key to the new understanding is the realization that the amount of energy organisms squeeze out of their food depends on how much food they have. Give them abundant food and they use it inefficiently. When we combine this with the notion that organisms with different food-utilizing strategies are also affected in different ways by genetic mutations, then we discover a new principle, one in which both the fit and the unfit coexist indefinitely."

Dr Ivana Gudelj, also from the University of Exeter, said: "The fit use food well but they aren't resilient to mutations, whereas the less efficient, unfit consumers are maintained by their resilience to mutation. If there's a low mutation rate, survival of the fittest rules, but if not, lots of diversity can be maintained.

"Rather nicely, the numbers needed for the principle to work accord with those enigmatic experiments on bacteria. Their mutation rate seems to be high enough for both fit and unfit to be maintained."

Dr. David Lipson of San Diego State University, concluded: "Earlier work showed that opposing food utilization strategies could coexist in complex environments, but this is the first explanation of how trade-offs, like the one we studied between growth rate and efficiency, can lead to stable diversity in the simplest possible of environments."

http://www.sciencedaily.com/releases/2011/03/110327191044.htm