Evolution: Onward and Downward
A story in New Scientist explores a growing realization about evolutionary trees: over time, things have gotten simpler, not more complex. Better cut down the tree in your textbook and start over.
If you want to know how all living things are related, don’t bother looking in any textbook that’s more than a few years old. Chances are that the tree of life you find there will be wrong. Since they began delving into DNA, biologists have been finding that organisms with features that look alike are often not as closely related as they had thought. These are turbulent times in the world of phylogeny, yet there has been one rule that evolutionary biologists felt they could cling to: the amount of complexity in the living world has always been on the increase. Now even that is in doubt.
While nobody disagrees that there has been a general trend towards complexity – humans are indisputably more complicated than amoebas – recent findings suggest that some of our very early ancestors were far more sophisticated than we have given them credit for. If so, then much of that precocious complexity has been lost by subsequent generations as they evolved into new species. “The whole concept of a gradualist tree, with one thing branching off after another and the last to branch off, the vertebrates, being the most complex, is wrong,” says Detlev Arendt, an evolutionary and developmental biologist at the European Molecular Biology Laboratory in Heidelberg, Germany.
The article goes on to describe a new storytelling strategy.
The entire tree of life has been built on the assumption that evolution entails increasing complexity. So, for example, if two groups of animals were considered close because both had a particular prominent feature, then someone discovered a third, intermediate line that lacked that feature but shared many other aspects of the two groups, traditional phylogenists would conclude that the feature had arisen independently in the two outlying groups, by a process known as convergent evolution. They often did not even consider the alternative explanation: that the feature in question had evolved just once in an ancestor of all three groups, and had subsequently been lost in the intermediate one. Now a handful of molecular biologists are considering that possibility.
How the earlier, more primitive creature evolved the innovation in the first place was left unstated. These innovations are not simple functions likely to arise from genetic mutations. They include multi-part systems, such as a central nervous system.
The Darwin Party’s motto is, “Everything we know is wrong.” If you like trying out the avenues with signs that say Wrong Way, follow the Darwin Partymobile onto the highway of life.