From: Anders Sandberg (asa@nada.kth.se)
Date: Tue Nov 05 2002 - 02:17:49 MST
On Tue, Nov 05, 2002 at 12:26:44AM -0800, Zero Powers wrote:
> >From: spike66 <spike66@attbi.com>
>
> >Question please, evolution wonks: since most
> >mammals have multiple offspring and consequently
> >have 4 pairs of nipples, are humans ever born with
> >vestigial extra pairs of nipples?
>
> A similar question I've wondered about from time to time is: Why do *men*
> have nipples?
Because the default is to be a female. The fetus starts to
develop into a male as various regulatory genes are activated
by hormones. The development of nipples and milk ridges start
(in week three or four) before these genes really come online
(in week seven), so the nipples are vestigial in males. They
seldom cause trouble, so there is no evolutionary pressure to
get rid of them.
There can be a small amount of milk-producing tissue there (in
fact, up to puberty the amount of mammary glands seem to be
roughly equal between the sexes), so with sufficient estrogen
treatment males can produce milk. Something for the transhuman
familiy?
Hmm, having both parents give milk might actually be smart.
The infant receives antibodies and immune information from the
milk, and having both parents provide it might make a immune
system with broader protection. Any data on the effects of
providing infants with breast milk from several people?
-- ----------------------------------------------------------------------- Anders Sandberg Towards Ascension! asa@nada.kth.se http://www.nada.kth.se/~asa/ GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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