Evolution quiz

Pratt Museum,
Homer, Ala.

Invisible evidence
Until recently, the bedrock evidence for evolution came from fossils. It was Georges Cuvier, back in 1817, who first noticed that fossils found in higher layers of rock were more similar to modern creatures than those found in lower layers, or strata. Cuvier deduced that lower strata were older, and that piles of rock contained a record of biological change through the ages.

For more than 100 years, paleontology, the study of ancient life, remained the foundation of evolutionary science. The fossilized remnants of dinosaurs, trilobites and various other marine organisms showed how species appeared, evolved and disappeared over the eons. Fossil studies concentrated on structure: When did the three-part body of the insect and crustacean first appear? When did the backbone originate? What about the opposable thumb, the defining characteristic of primates?

Fossil evidence showed, for example, a string of human ancestors that appeared one or more million years ago in Africa. But recently, the fossil record has been augmented by intriguing genetic and biochemical evidence for evolution.

Instead of looking at anatomy -- the number of legs or shape of the mouth, or the presence, say, of scales as opposed to feathers or fur, the new evolutionists look at molecular structure. Which proteins are used, and which genes make them? How similar are genes and proteins among various organisms?

The result of this work provides an entirely new reason to believe that evolution has shaped life since the beginning, says Washington University biologist Goodenough. "In the past 10 or 20 years, we have developed this completely independent record. Studies of the genome [an organism's genetic code] have in most cases completely confirmed...the relationships deduced from the fossil record."

Naturally lazy
The analyses depend on biochemical and genetic techniques invented during the past half century, and on the fact that nature is kinda, can we say lazy? Like humans, nature seldom reinvents the wheel. Humans, after all, adapted the wheel of an applecart to use on a bicycle, and then altered it further for the needs of the Indy car, airplane and moon rover. Each "improvement" retained elements of the original invention, but adapted it to work in a new environment.

The analogy breaks down when we get to design: Wheels have designers, but evolution does not. Instead, random changes in genes -- mutations -- supply variations that are sifted by natural selection. The majority of mutations are unhelpful or deadly, and they tend to disappear from the gene pool; mutations that promote survival and reproduction are retained. And while a bicycle designer can rummage through a shelf of wheel styles, nature does not warehouse genes and distribute them as needed. With few exceptions, organisms get all their genes from their parents.

Getting back on track... Nature's parsimony is old news to evolutionary scientists. The fins of a whale (a marine mammal descended from land animals), retains the bone structure of a land mammal's hand, as does the wing of the flying mammal called the bat. Since the backbone was "invented" by evolution hundreds of millions of years ago, it proved so useful that a huge list of animals descended from the first backboned creatures -- T. rexes and great white sharks, kangaroos and black-footed ferrets, to name a few.

What does this have to do with DNA and evolution?

©1999, University of Wisconsin, Board of Regents.