Henry R.S. contributes (14.9.03)

Gorillas have very small penises if that helps?

Noel sends (06.03):

Part of an answer, taken from

http://www.madsci.org/posts/archives/may2001/989331026.Ev.r.html
is:

Differences in chromosome number seem to be one form
of barrier to inter-breeding between individuals of
related species, but as I think you will see below,
some differences in chromosome number might just be
coincidental with some other species barrier.
... humans have 23 pairs of chromosomes, while
chimpanzees, gorillas, and orangutans have 24 pairs.
Each end of human chromosome number 2 (the second
largest human chromosome) looks very similar to the
long end of a pair of gorilla or chimpanzee
chromosomes, suggesting that the common ancestor of
these three species had 24 chromosomes and that humans
lost one chromosome due to translocation sometime in
the six million years that have passed since that
ancestral species lived.

Barriers To Interbreeding

Now differences in chromosome number do not serve as
reproductive barriers between all species. For
example, lets look at some of the equine species
(horses and donkeys). Domesticated horses have 32 pairs
of chromosomes and Donkeys have 31. Yet, they can
produce offspring, mules, which have 31.5 pairs of
chromosomes. One of the horse chromosomes goes
unpaired. Wild mountain zebras have 16 pairs of
chromosomes, while the last species of wild horse
(Przewalski's Horse) has 33 pairs. However, all of
these equine species can produce hybrid offspring. In
all of these crosses but one, the offspring are
sterile. It has long been argued that this sterility
is due to the difference in chromosome number, but
hybrids of the wild (33 pairs) and domesticated horse
(32 pairs) are fertile, and have 32.5 pairs of
chromosomes. So clearly, something more than just
differences in chromosome number is contributing to
the species interbreeding barrier.

--

Isn't this fascinating? And bizarre.