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Piecing Together Evolutionary History By Bridging The Gap Between Genetics And Paleontology

November 8, 2012
Image Caption: Pakicetus is a genus of extinct terrestrial carnivorous mammal of the family Pakicetidae which was endemic to Pakistan from the Eocene (48–49 Ma). Most paleontologists regard it as a basal whale closely related to the direct ancestors of modern day whales. Credit: Nobu Tamura/Wikipedia (CC BY 3.0)

April Flowers for redOrbit.com – Your Universe Online

Developmental genetics and paleontology seem worlds away from each other and the gulf between fossils and petri dishes seems insurmountable. Even the essential questions of the two disciplines are miles apart. Paleontology strives to determine “What happened in evolution?”, while developmental genetics uses gene control in embryos to try to answer “How did it happen?” Scientists have been combining the two, however, with some remarkable results.

A science team from Northeast Ohio Medical University (NEOMED) reviewed recent studies that used modern genetic techniques to shed light on fossils, or vice versa, in the current issue of the Journal of Vertebrate Paleontology.

“It is a very exciting time to be an evolutionary scientist. So many researchers are investigating evolution, either by finding new fossils or by figuring out the genes that underlie changes in evolution. Now it is possible to combine those two fields and go beyond what each field could have accomplished on its own,” said Dr. Hans Thewissen, Ingalls-Brown Professor for NEOMED.

The profound evolutionary changes that brought about some of the more spectacular animals of today and the past, including dolphins, whales, snakes, bats, elephants, and dinosaurs are discussed in the review. For example, transition from a four-legged ancestor to a current form with two forelimbs, like a dolphin, or no limbs, such as a snake, seems like a huge evolutionary leap. However, transitional fossils have been discovered that bridge these gaps and using developmental genetics, scientists have discovered that although these are large changes in shape, they are relatively small changes in just a few genes.

Thewissen says that recent research has also discovered that similarly shaped organisms may not have experienced similar developmental changes in their history. Although snakes and cetaceans — whales and dolphins — both lost limbs independently from their respective ancestors through evolution, they did so in very different ways. Snake bodies modified to have no neck region, leaving no room for forelimbs. No limb buds form in that region of the body during embryonic development. Snake embryos do still develop hind limb buds, but the genes that control their growth have been transformed during the course of evolution so that hind limbs never develop. Different developmental mechanisms can be at work even in the evolutionary history of a single animal.

Dr. Thewissen says, “For me personally, as someone who has spent most of his life studying fossil whales, it is very exciting to be able to use information from the development of living mammals, and use it to teach me about how whale evolution happened, 50 million years ago.”

The review revealed that scientists can even modify the genetic code of living animals to replicate changes observed in the fossil record. Heightened activity of a particular gene in mouse embryos, for example, causes their teeth to grow larger. Similar changes occurred during the course of elephant evolution — early elephants had teeth less than an inch long, while modern elephants have teeth over a foot in length — and the changes that brought about this increase in size in elephants may resemble the once that are induced in laboratory mice.

This multi-disciplinary approach was once rare, but today is increasingly common.

Dr. Lisa Noelle Cooper of NEOMED said, “At a time when most of science is hyper-specialized, my hope is that the newest generations of scientists are able and unafraid to approach research questions using a variety of techniques.”


Source: April Flowers for redOrbit.com - Your Universe Online