Researchers say they've scored one more for evolution.
Scientists have presented archaeological evidence, anatomical evidence and now they say they have genetic evidence that demonstrates Charles Darwin was right when he suggested new species arise through a process known as natural selection. Skeptics of the theory, however, remain unconvinced.
A team led by William McGinnis, a biologist at the University of California at San Diego, showed that a single mutation in a particular class of genes known as Hox genes can lead to big changes in the body. These big changes, the researchers say, could have played a significant role in the evolution of some new species.
A Master Switch
Past research has shown that Hox genes act as master switches that turn on and off other genes during embryonic development. The team found that by mutating Hox genes in multi-limbed crustaceans and millipedes they could effectively block the development of limbs in these animals.
This mutation, they say, could have led to the evolution of insects, which have only six legs and emerged suddenly some 400 million years ago, long after crustaceans were on the scene.
"One of the big questions people have for evolution is, How can you get dramatic rearrangements of bodies," said McGinnis. "Up until now there hasn't been much evidence of how this happens."
The study by McGinnis and graduate students Matthew Ronshaugen and Nadine McGinnis appears this week as an early publication in the online version of the journal Nature.
Challengers of evolution say they remain unconvinced.
Creationists argue that, rather than evolving naturally, all species were created by God. And proponents of a theory known as Intelligent Design claim that plants and animals are too complex to be formed by evolution and so must have been crafted by some existing intelligence (possibly God or a form of extraterrestrial life).
Both contend the evidence is too thin to support the idea of evolution and the genetic study doesn't dent their skepticism.
"There's an awful lot more to a species change than eliminating some legs," says Jonathan Wells, a biologist and senior fellow at the Discovery Institute, a Seattle research institute that promotes the Intelligent Design theory. "In effect, all they've produced is a crippled shrimp."
David DeWitt, a creationist and associate professor of biology at Liberty University in Lynchburg, Va., says the scientists "have a good example of how mutations can yield a loss of information." But, he adds, that doesn't show how new species gain new features — like a set of wings where before there were none.
McGinnis acknowledges his team's studies can't explain all the changes that must have occurred for shrimp-like animals to evolve into insects. But he says his studies show the Hox gene makes a "huge contribution" when it comes to removing extra limbs.
He adds that the genetic changes would not have happened within one generation of shrimp, but over several. That kind of time, he says, would have provided room for healthy mutated animals to emerge and not just "cripples."
Americans and Evolution
Darwin first proposed his theory of evolution 143 years ago when he published his book Origin of Species. The book fundamentally changed the way scientists looked at biology although it was also met with a surge of outrage and criticism.
Today, many still challenge the idea — polls show that the number of Americans who believe in evolution is less than half, or about 45 percent. And state school boards in Ohio and Indiana are now considering introducing creation and Intelligent Design theories into classroom textbooks.
But Jerry Coyne, an evolutionary ecologist at the University of Chicago, argues that scientists have plenty of evidence for evolution, including archaeological remains of transitional species and so-called vestigial organs in living animals that are left over from their evolutionary ancestors.
He says the new work showing how dramatic changes might occur in an animal is "interesting, but unnecessary."
"The evidence for evolution doesn't rest on this experiment," he said. "We don't need it."