Rick asks:

>I've heard that a male gorilla will mate with all the females in his family.
>So how do gorillas avoid the birth defects associated with incest?

The almost ubiquitious pattern in mammals is that males, once they reach
maturity, are forced out of their natal groups and must fight their way back to
a position of dominance in another group, either as the harem or lek master or
a male capable of holding prime territory, before they breed. This pattern
assures that only males who have demonstrated their vigor and absence of
primary congenital defects sire the next generation.

But gorillas reverse this pattern. "Unique among higher primates, all females
leave their natal group, joining another group or a solitary male. Sons may
stay on to take over the leadership. Other males may leave to set up their own
group. Young adult males may be allowed to join a group for a few hours to
several months. But most males without families live alone until they can steal
a female to start a family. 

"Gorillas live in extended family groups, which average 5-10 but ranges from 2
to 32. The fully mature male has a light 'saddle' of nearly white fur that runs
down his back, side and flank; and is hence called a silverback. A group
generally comprises 1-2 silverbacks, 6 females and several juveniles and
infants. Among the males, there is a clear hierarchy based on size and only the
dominant silverback male breeds. He leads his family group and decides where
they feed and sleep. When relaxed, the leading silverback is the centre of
attraction for the females and the young -- it is almost invariably they who
move to sit by him, or to follow him, not vice versa. Females are strongly
bonded to the male and not to each other. The females are often
"acquired" by
the male one at a time, by luring or abducting them from their families as
adolescents. Females are ranked by the time they were "acquired",
highest to
the first female acquired."

     -- http://www.szgdocent.org/pp/p-gorilla.htm

Wirt Atmar
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