Re: Question


Bruce Watson wrote:
Humans are the only primates that don't have pigment in the palms of
their hands.

What reason compatible with evolution explains this?

Some quick speculations:

One possible reason is that a lack of pigmentation on palms and soles
of feet is a plieotropic effect of selection for hairlessness on palms
and soles.

Yamaguchi et al.
(http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15117970&query_hl=16)
show that paloplantar surfaces have five times as high a concentration
of DKK1 as the rest of the skin.

In other research,
(http://www.jcb.org/cgi/content/full/165/2/275#Discussion) Yamaguchi
notes that DKK1 transgenic mice, in addition to lacking pigment, also
lack hair. It could be that DKK1 concentration in palms and soles was
simply an efficient way to keep them free of hair (whether or not it's
more efficeint than other mechanisms, I have no idea, could be a
founder effect thing) and a lack of pigmentation was simply a (more or
less neutral) side effect.

I suppose I'd have to know a lot more about pigmentation in the palms
and soles of other primates in order to make that a viable hypothesis,
but it's at least a potential explanation.

(Disclaimer IANA Genetecist, so I'm almost certainly wrong and will
presently be admonished by someone who knows what s/he is talking
about. I offer my thanks for the correction in advance.)

.

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