Monday, March 13, 2006

Study Claims 'Most Evolved' Species Found


Most people have heard of cockroaches and crocodiles as being "old" species since they haven't evolved much in the past hundred million years. But what would be considered a genetically "new" species and which are the "newest"? This is the question that two Princeton geneticists set out to answer.

Using the GenMAPP Gene Database, whose goal is to systematically store and categorize all of the world's genetic diversity, Dr. Gene Jenson and Dr. Alice Bratoa are using DNA analysis to weed out the old from the new.

"One of the most difficult aspects of this study was coming up with a working definition of what 'genetically new' is," said Bratoa. "We wanted to find species that have had the most 'branching' along their evolutionary path." They have theorized that they couldn't just find the most genetically unique beings because they are generally known as the oldest. Bacteria, for instance, are one of the most genetically distinct beings but they lack even a nucleus. On the other hand, finding the most genetically mundane living thing is even harder to define and yields such golden oldies as cockroaches and sharks.

The 'timepiece' that geneticists most often use are the genetic mutations that are found in the "empty" regions of the genome - the parts that seem to have no effect on how the being is developed or behaves. These accumulate at a semi-fixed rate over generations. The beings that accumulated the most of these harmless mutations are thought to be the oldest.

But the geneticists added another layer of complexity to ensure that the species had to endure the most branching before being labeled "most evolved". Within the group of species that had the most mutations that were harmless, they sought the ones who were then the most genetically distinct.

Then they looked through some of the major branches of evolution for their winners. "We couldn't just pick one winner," explained Jenson. "It's like comparing apples and oranges. The gulf between plants and animals is to great to make an adequate comparison."

In the plant kingdom, they have concluded that a wild fig tree was the most evolved tree and the orchid called creeping ladies tresses was most evolved among all plants. Yucca moths claimed the rights for the animals while the California red-backed vole holds it for the mammals and the greater honeyguide has it for the birds. Humans were on the "short list", Jenson said, but among primates our close ancestor the orangutan supercedes us.

Once they looked more closely at these species, they discovered that they all had two things in common. One was that they are highly specialized. The other is a survival strategy known as mutualism, a symbiotic relationship with another species where both species benefit from their relationship. Fig trees require a species-specific fig wasp to penetrate its fruit and pollinate it from inside, giving the wasp a place to lay her eggs. The creeping ladies tresses require a specific bee species to slip into its nectar and climb out through a special hole where two pollen sacks are glued on so it can pollinate another orchard. Yucca moths have a similar relationship with the yucca plant. Red-backed voles eat fungi, helping to disperse their spores. And honeyguides have a mutually beneficial relationship with humans; these birds lead people to hives where the humans take the honey and the bird eats the leftover larva and wax.

Dr. Bratoa speculates that these relationships force these species to change more rapidly since they would have to change not only for their own survival, but for their partner's as well.

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