A recent study by biologists has conclusively revealed that developmental evolution is deterministic and follows an orderly pattern.
The researchers came forward with the new theory by studying how development evolves in organs which themselves do not change.
For the research work, the team examined the vulva (the female's copulatory and egg-laying organ) in nearly 50 species of roundworms.
Because the vulva does not significantly change across species, it might be said that there would be little variation in vulva development.
However, the researchers found an astonishing amount of developmental variation. They then reasoned that this variation, since it did not affect the final adult vulva, should have evolved in a random fashion.
In executing the study, the research team analyzed 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 the researchers had expected.
In addition, they found that evolutionary changes among these species were unidirectional in nearly all instances.
For example, they concluded that the number of cell divisions needed in vulva development declined over time, instead of randomly increasing and decreasing.
In addition, the team noted that the number of rings used to form the vulva consistently declined during the evolutionary process.
These results demonstrate that, even where we might expect evolution to be random, it is not.