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posted: 4/15/2013 11:33 AM

All life evolved from a universal common ancestor

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  • An image of sea life during the Cambrian period, the time spanning 542 million to 488 million years ago when life-forms quickly diversified, is seen in this curved projection surrounding visitors at the Field Museum's Evolving Planet exhibit.

      An image of sea life during the Cambrian period, the time spanning 542 million to 488 million years ago when life-forms quickly diversified, is seen in this curved projection surrounding visitors at the Field Museum's Evolving Planet exhibit.
    Courtesy of Greg Neise/The Field Museum

 

You wanted to know

"How did people and animals come to exist?" asked Katherine Crawford's fifth-grade students at West Oak Middle School in Mundelein.

A dark, choking environment with little oxygen and water. Erupting volcanoes spewing toxic gases. One giant supercontinent.

That's what Earth looked like more than 3 billion years ago at the very point in time when life began.

Despite these unliveable conditions, a universal common ancestor emerged, one cell that most likely contained double-stranded DNA, which carries the genetic puzzle pieces for life. All life evolved from this universal common ancestor.

Fast forward to today. About 7 million species exist on Earth that evolved from this single universal ancestor, and still more species have lived and thrived, like dinosaurs and dodos, that are now extinct.

"We are the current products of an evolutionary history that goes back 3.5 billion years," said Jerry Coyne, University of Chicago professor, Department of Ecology and Evolution.

"We started with self-replicating molecules and that transitioned to the millions of species on Earth today. Plants, bacteria and everything has a common ancestor, and we are all related."

How is it that scientists have identified that the hundreds of thousands of diverse forms of life -- plants, animals, fish, fungi, bacteria, algae and people -- could have stemmed from one source?

"All species have the same genetic code using the same sequences of DNA. That can only mean that the code evolved once; it's too complicated to evolve identically several times," Coyne said.

In his book "Why Evolution is True," Coyne explains how life leapt from one universal ancestor to more than 7 million species living today.

"Life on Earth evolved gradually, beginning with one primitive species -- perhaps a self-replicating molecule -- that lived more than 3.5 billion years ago; then it branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection."

Some species have evolved very slowly. The ginkgo trees that shade parks and roadways are almost identical to ginkgo tree fossils dating back 270 million years. Horseshoe crabs also are similar in appearance to their ancient predecessors.

However, birds come from a long line of constantly evolving species; their dinosaur ancestors didn't survive the evolutionary chain.

Charles Darwin's book "On the Origin of Species," published in 1859, established the science of evolution. Darwin's book detailed how biological diversity comes from speciation, the process in which new species develop.

Research with DNA sequencing, made possible in the past 30 to 40 years, has confirmed the connections among species and demonstrated the evolutionary process in action.

Coyne's research in evolutionary biology focuses on crossbreeding species of fruit flies and studying the resulting gene differences.

"This is the same process by which biological diversity comes about," he said.

Coyne and his colleagues hope to determine the role specific genes play in the evolution of diversity of the fruit fly -- the number, location and effects of the genes that cause various species of the flies to originate.

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