and sons, brothers, male cousins, uncles and nephews, etc. In the case of females after puberty, there is no
reason to think they will be mothers and daughters, sisters, or aunts and nieces, because they disperse
far and wide at puberty.
Vigilant et al. (2001) initially tested this prediction in three communities of the Taï chimpanzees of
Ivory Coast and in the Gombe chimpanzees. In contrast to earlier studies, they found that the males
were not more closely related to each other than were females. This was attributed to two factors: gene
flow between communities mediated by females, and the inability of individual males to monopolize
females so that offspring are fathered by a variety of individuals.
We are now finding the same at Sonso. The original model of chimpanzee population dynamics, with
males more closely related than females, may be wrong. Our Sonso males appear to be no more closely
related to each other than females are (Lukas et al., in press).
This question of the relatedness of males is of especial interest because it has been believed hitherto
that the reason that community males often associate with each other and move around together more
than females do is that the males are close kin, whereas the females are not. The same argument has
been used to explain the communal hunting of monkeys and other prey by males, the communal
patrolling and defence of the community’s range by males, and their concerted attacks on members of
other communities. It now seems not to be close genetic relatedness as such that underlies these actions.
In addition, Mitani et al. (2000, 2002) have shown that males who are close maternal kin are no more
likely to co-operate for grooming, or keep close to each other, than less closely related males. They con-
clude that rank and age are more important than kinship in determining male–male affiliations. It seems
therefore that we shall have to re-think our theories of the basis of the co-operative behaviour we see
between community males.
What have we been able to discover about the kinship relationships that do exist between
Sonso individuals? This can be broken down into questions of (a) maternal kinship and (b) paternal
kinship.
Maternal kinship
In the case of offspring born since the Project began, we know the mothers. For individuals born before
the Project started, in several cases we allocated them putative mothers on the basis of their behaviour;
in the following cases genetic evidence has confirmed that they are indeed mother–offspring pairs: Nick
is the son of Ruhara; Gonza is the daughter of Zimba; Musa is the son of Nambi; Bob is the son of Ruda;
Kewaya is possibly the daughter of Zimba.
Paternal kinship
We have no evidence that the fathers recognize their offspring and so we conclude that father–child
relationships are not known to chimpanzees. As we saw in Chapter 6, males compete for access to
sexually receptive females and in consequence there is differential reproductive success, which is to
some extent linked to status. We therefore expect that alpha males will have a disproportionate number
of offspring. The two alpha males since we have been observing the Sonso community have been
Magosi who was alpha male until 1995, and Duane who took over in that year.
Table C.1 shows the paternities that can be attributed with confidence on the basis of the genetic
results we have obtained so far. Not all offspring are included; in some cases samples have yet to be
obtained, in others the DNA has yet to be sequenced. Mothers are also included in the table.
Genetics of the Sonso community 249