176 ■ FLOWThroughout history, people have been born into and have spent
their entire lives in kinship groups. Families have varied greatly in size
and composition, but everywhere individuals feel a special intimacy
toward relatives, with whom they interact more often than with people
outside the family. Sociobiologists claim that this familial loyalty is
proportional to the amount of genes that any two persons share: for
instance, a brother and a sister will have half their genes in common,
while two cousins only half as many again. In this scenario siblings will,
on the average, help each other out twice as much as cousins. Thus the
special feelings we have for our relatives are simply a mechanism de
signed to ensure that the genes’ own kind will be preserved and repli
cated.
There are certainly strong biological reasons for our having a
particular attachment to relatives. No slowly maturing mammalian spe
cies could have survived without some built-in mechanism that made
most adults feel responsible for their young, and the young feel depen
dent on the old; for that reason the bond of the newborn human infant
to its caretakers, and vice versa, is especially strong. But the actual kinds
of relationships families have supported have been astonishingly diverse
in various cultures, and at various times.
For instance, whether marriage is polygamous or monogamous, or
whether it is patrilineal or matrilineal, has a rather strong influence on
the kind of daily experiences husbands, wives, and children have with
one another. So do less obvious features of family structure, such as
specific patterns of inheritance. The many small principalities into
which Germany had been divided until about a century ago each had
laws of inheritance that were based either on primogeniture, where the
oldest son was left the entire family estate, or on an equal division of
the estate among all sons. Which of these methods for transmitting
property was adopted seems to have been due almost entirely to chance,
yet the choice had profound economic implications. (Primogeniture led
to concentration of capital in the lands that used this method, which
in turn led to industrialization; whereas equal sharing led to the frag
mentation of property and industrial underdevelopment.) More perti
nent to our story, the relationship between siblings in a culture that had
adopted primogeniture must have been substantially different from one
in which equal economic benefits accrued to all children. The feelings
brothers and sisters had for one another, what they expected from one
another, their reciprocal rights and responsibilities, were to a large
extent “built into” the peculiar form of the family system. As this
example demonstrates, while genetic programming may predispose us to