-C. Paula de los Angeles
Question: "If the broad evolutionary diversification of a group of organisms were repeated by a few species in a single genus tens of millions of years after the group's initial diversification, what would that say about the roles of contingency, constraint, and adaptation?" (Science Daily 2009)
According to Darwin, natural selection leads to the gradual adaptations of individuals and populations over time. The article uses the example that we know that most cats look like cats, develop like cats, but have a fossil record that shows less than cat-like ancestors. Each subgroup has a similar story. What does it say about evolution if this historical diversification were repeated again in the future? What is the probability that these same adaptations be to due to chance again?
A study to be published in Proceedings of the Royal Society by Dr. Scott Lidgard details the discovery of a species, cheilostome bryozoans, marine animal colonies, who independently repeat the small step-by-step adaptations that occurred 80 million years ago in the Cretaceous Period.
The adaptations go from soft feeding organs in a flexible membrane, then to calcified spines around the membrane, then fusion of the spines, then reduction of the fused spinal shield and membrane, and then the invention of a water sac to squeeze out of the organ.
The evolutionary trajectory was repeated.
This discovery seems to be strong evidence for the argument of adaptation vs. genetic drift. Is evolution just by chance? I would like to read more of the actual paper to see how the environments differed over time. Also, while this is one isolated case of this happening and a specific example, we should be hesitant to support adaptationism in all cases, as there are lots of examples where this doesn't happen. Interesting.
News link here: http://www.sciencedaily.com/releases/2009/06/090609220721.htm