With evolution, scientists must watch out for unexpected twists and turns

Column: We know a lot about life on Earth, but we're still learning fundamental insights all the time.

Biologists have learned a lot about evolution since Darwin published his theory 100 years ago. But nature can still surprise them.

Sometimes it's a new fundamental insight. The discovery that an ancient merger of microbes opened an unsuspected evolutionary pathway for higher organisms gives biologists a new perspective on earthly life. In announcing this on August 20, molecular biologist James Lake said that it now is clear that "higher life would not have happened without this event."

Or, sometimes it's a tweak to our understanding of an evolutionary detail that has consequences for our time. A new look at 200 million years of marine clam evolution reveals that some closely related clusters of species are more vulnerable to extinction than are life forms generally. Announcing this research a few weeks ago, evolutionist Gene Hunt said this shows that big extinctions "tend to preferentially cull the more vulnerable lineages, leaving the resistant ones to proliferate afterward." The lesson for conservationists: if you want to preserve species diversity, seek out the vulnerable and give them extra protection.

The take away lesson for the rest of us is not to take present scientific knowledge of evolution for granted either in speculating about the development of life on Earth or in environmental planning. What we don't know can trip us up.

Commenting on discovery of that microbial merger over 2.5 billion years ago, Carl Pilcher, director of NASA's Astrobiology Institute, called it "a major advance in our understanding of how a group of organisms came to be that learned to harness the Sun and then affected the greatest environmental change Earth has ever seen."

Those organisms were the cyanobacteria that evolved photosynthesis. Their production of oxygen changed the atmosphere's chemical composition, preparing the way for evolution of more complex organisms including plants, animal, and humans.

The Astrobiology Institute is a collaboration of NASA with scientists in 14 US teams and 6 international consortia. It exists more on the Internet than at any one institution. In this case, Dr. Lake from the University of California at Los Angeles is carrying out the research. He has reported the details in the Aug. 20 online edition of Nature. The microbes that merged and evolved into cyanobacteria were a type of single-celled organisms called prokaryotes. Lake found evidence of that merger in comparing proteins from more than 3,000 different prokaryotes living today.

Dr. Hunt at the Smithsonian Institution, Kaustuv Roy at the University of California in San Diego, and David Jablonski with the University of Chicago reported the research on extinction in Science. They believe their study of a global database of bivalve fossils reveals a universal fact of evolution. As Dr. Jablonski stated it, "Both background extinctions, which represent most extinctions in the history of life, and mass extinctions tend to be clumped into particular evolutionary lineages."

In other words, when it comes to extinctions, evolutionary history tends to be destiny. The evolutionary path of some related clusters of species has made them less resistant to extinction pressures than are other lineages.

Darwin's principle of evolution through natural selection still guides research on earthly life's history. But scientists must watch out for unexpected twists and turns.