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Alan Brush on the Scientific American feathers paper
Alan Brush was kind enough to let me share his comments about "Which Came
First, the Feather or the Bird," by Richard O. Prum and Alan H. Brush,
published in the March 2003 issue of "Scientific American."
I think the most important point of the paper and all the work that it
summarizes, is an understanding of the evolution of a novelty. From the
work on the feather keratins, the nature of the genes that produce them,
and their functional abilities to form filaments, we have an elemental
understanding of the molecular/cellular aspects. Prum's modeling of
development put a dynamic aspect of a huge body on developmental
morphology created in the 1930's and 1940's. This brings to center stage
an important understanding of the individual steps and their
incorporation to a developmental program capable of producing a
remarkable morphology diversity. We understand the diversity of feathers,
and now basically have a time line for the evolution. Each stage is
adaptive. Evolution has no foresight! Finally, there is all the recent
fossil evidence for the evolution of feathers. What is found in the
record is closely related to what is found in ontogeny. Quite a
remarkable story. Both Rick and I feel privileged to be working in this
area and watch it emerge.
The folks at Scientific American did a remarkable job with the art work.
The diagrams are especially useful. The reconstruction of the animals are
excellent. Even the appropriate flora is indicated in the paintings. We
were insistent on spanning the science from gene activity to feather
function. Their editors worked with us to conserve language without
'dumbing-down' in terms of technical terms. It was, overall, a satisfying
experience. The entire thing afforded us the opportunity to express some
ideas that have been controversial and still rattle some chains. But our
interpretation was careful and conservative.
What is still left? Well, the entire subject of the control of moult at a
molecular level and the changes in gene activity patterns involved for
one thing. More detail on what produces feather shape and size is
interesting. I still muse over the mechanisms that control the plumage
patterns, but that's enough for another career or two.
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