brad writes:
I am somewhat concerned that we might be playing a bit too loosely with meaning of words, "null", "neutral", and "zero". I would have simply thought that there are NO body parts that have no "cost".
Agreed. All body parts have some cost. The term 'neutral body part' seems to be interpreted differently by each poster (myself included).
Hector's query of gman:
Lots of neutral body parts would not be neutral at all. It would be disadvantagious to have lots of neutral body parts, which natural selection would prevent from happening.
To respond to this adequately we need to be sure of what definition of 'neutral body part' gman intends.
I take it to mean a non-vestigial appendage, growth, organ, blastocyst, etc. that is the result of random mutation that provides NO competitive advantage or disadvantage.
Ergo an Emu's wings would not be considered neutral, but perhaps something like the lack of wisdom teeth in homo sapiens is.
It's possible gman is confusing vestigial 'body parts' (pelvis in snakes, coccyx in humans, etc.) with a distinct, benign mutation that has conveys no competitive advantage.