Am I Learning Some Biology?
I had written before that I was very impressed with Endless Forms Most Beautiful by Sean Carroll. Perhaps I have learned some biology when I read it. I was able to actually follow the post at Pharyngula.org on the number of thoracic veterbrae in mammals. It talked about Hox which were a major topic of Endless Forms, as was the concept that genes have different effects depending on when they are turned on, which is my translation of this quote.
Genes exhibit bewilderingly complex patterns of expression, and pleiotropy (the regulation of multiple phenotypic characters by a single gene) is the rule, not the exception.