Finding: Biologists in an international team have concluded that developmental evolution is deterministic and orderly, an not the random sequence operation many previously believed based on a study of different species of roundworms.
If organs do not change, how does evolutionary development work in those organs?
Enter the study involving the female copulatory and egg-laying organ, the vulva, found in nearly 50 species of roundworms. The conventional wisdom is that because the vulva does not significantly change across species, one might predict that there would be little variation in vulva development. But that is not the case. Researchers found a lot of developmental variation. They concluded that this variation, since it did not affect the final adult vulva, could not have evolved in a random, fashion.
The research team looked at more than 40 characteristics of vulva development, including cell death, cell division patterns, and related aspects of gonad development. They plotted the evolution of these traits on a new phylogenetic tree, which illustrates how species are related to one another and provides a map as to how evolutionary changes are occurring.
Their results showed an even greater number of evolutionary changes in vulva development than they had expected. But they found that evolutionary changes among these species were unidirectional in nearly all instances.
The decline of cell divisions
For example, they concluded that the number of cell divisions needed in vulva development declined over time instead of randomly increasing and decreasing.
The decline of number of rings
In addition the number of rings used to form the vulva consistently declined during the evolutionary process.
These results demonstrate that, even where you might expect evolution to be random, it is not.