Where Fossils Fear To Tread: Scientists Follow Genes To An Ancient Ancestor

August 13, 1997

Some 600 or 700 million years ago, before animal life made a sudden evolutionary shift and diverged into nearly all the major animal divisions we know from fossils, primitive animals were inventing the genes that would make it all possible.

No one knows what it looked like. There is virtually no clear fossil evidence. But now scientists believe they have found a way - using genes preserved in and common to modern animals - to look past the fossil record to our most distant common ancestors.

Writing this week (Aug. 14) in the journal Nature, and following up on a series of recent papers, molecular biologist Sean Carroll of the Howard Hughes Medical Institute at the University of Wisconsin-Madison, Neil Shubin from the University of Pennsylvania, and Cliff Tabin of Harvard Medical School, sketch out a radical new way of looking back in time.

"The fossil record prior to the Cambrian is so scant nobody knows the origin of animal life," said Carroll. But now "we're drawing a picture of something no one has ever seen."

Carroll is one of a growing number of scientists now using the techniques of modern molecular biology to look into the murky waters of distant evolutionary biology. They are looking so far back that there are virtually no fossils or other physical clues to what the Earth's earliest animals were like.

But Carroll and others are now finding powerful evidence that an ancient common ancestor - a worm-like animal from which most of world's animals subsequently derived - invented a set of body-building genetic machinery so successful and malleable that it has survived to this day.

"This is stunning," said Carroll. "Nobody thought that this animal was so sophisticated. We're talking about the common ancestor of all the most successful animals on Earth."

What is so striking, according to Carroll, is that the genes used to grow appendages - legs, arms, claws, fins and antennas - were operational at least 600 million years ago, and that the genetic machinery is very similar in all animals past and present. What makes animals different, what differentiates a crab from a mouse or a fruit fly from an eagle, is simply how those genes are expressed, he said.

Until the advent of genetic techniques and recent work that has shown that animals, as embryos, share the same genetic machinery that governs body architecture, the only recourse for understanding how animals evolved different kinds of appendages was in the realm of comparative anatomy.

And appendages, said Carroll, have been used as classic examples of independent evolution. But now Carroll and his colleagues argue that the problem of developing limbs, be they claws or wings, was solved just once a very long time ago, and that the genetic mechanism is still at work.

"Everybody thought the wheel was invented again and again and again," Carroll said, "but there was a single solution and everything is a modification of that."

That argument is supported, said Carroll, by the discovery of the same appendage-making genes in six broad divisions of the animal kingdom, including vertebrates, insects and fish. The discovery, made in Carroll's lab, was reported last May in the Proceedings of the National Academy of Sciences.

"We found the same mechanism in all of these divisions of the animal kingdom. The architecture can vary tremendously, but the genetic instructions are the same and have been preserved for a very long period of time," he said.

The idea that a common set of genes is responsible for building appendages not only simplifies evolutionary history, but helps explain the great burst of evolutionary activity known as the Cambrian explosion. This "evolutionary big bang" took place in the world's oceans more than 500 million years ago when new animals appeared at breakneck speed.

"The reality is that animals with appendages took off and dominated the Earth," at that time Carroll said. "It was like an arms race" with animals that could swim faster, grab tighter and fight with greater effect dominating the ocean environment and conquering new ones like the land. During the Cambrian, animals got bigger and more diverse, but those changes did not require new genes.

The techniques being pioneered by Carroll and others are opening a new window to the past, said Carroll: "It's doing paleontology without fossils."
-end-


University of Wisconsin-Madison

Related Fossils Articles from Brightsurf:

First exhaustive review of fossils recovered from Iberian archaeological sites
The Iberian Peninsula has one of the richest paleontological records in Western Europe.

Fossils reveal mammals mingled in age of dinosaurs
A cluster of ancient mammal fossils discovered in western Montana reveal that mammals were social earlier than previously believed, a new study finds.

Oldest monkey fossils outside of Africa found
Three fossils found in a lignite mine in southeastern Yunan Province, China, are about 6.4 million years old, indicate monkeys existed in Asia at the same time as apes, and are probably the ancestors of some of the modern monkeys in the area, according to an international team of researchers.

Scientists prove bird ovary tissue can be preserved in fossils
A research team led by Dr. Alida Bailleul from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences has proved that remnants of bird ovaries can be preserved in the fossil record.

Biosignatures may reveal a wealth of new data locked inside old fossils
Step aside, skeletons -- a new world of biochemical ''signatures'' found in all kinds of ancient fossils is revealing itself to paleontologists, providing a new avenue for insights into major evolutionary questions.

Fish fossils become buried treasure
Rare metals crucial to green industries turn out to have a surprising origin.

New Argentine fossils uncover history of celebrated conifer group
Newly unearthed, surprisingly well-preserved conifer fossils from Patagonia, Argentina, show that an endangered and celebrated group of tropical West Pacific trees has roots in the ancient supercontinent that once comprised Australia, Antarctica and South America, according to an international team of researchers.

Ancestor of all animals identified in Australian fossils
A team led by UC Riverside geologists has discovered the first ancestor on the family tree that contains most animals today, including humans.

Metabolic fossils from the origin of life
Since the origin of life, metabolic networks provide cells with nutrition and energy.

Fossils of the future to mostly consist of humans, domestic animals
In a co-authored paper published online in the journal Anthropocene, University of Illinois at Chicago paleontologist Roy Plotnick argues that the fossil record of mammals will provide a clear signal of the Anthropocene era.

Read More: Fossils News and Fossils Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.