A POSITIVE CONCLUSION 36 itally a theory about limits. It takes current ranges in modern envi-
ronments as an expression of direct genetic programing, rather
than a limited display of much broader potential. If a feather acts
by featherness, we cannot change its behavior while it remains a
feather. If its behavior is an expression of broad rules ded to spe-
cific circumstances, we anticipate a wide range of behaviors in dif-
ferent environments.
Why should human behaviorial ranges be so broad, when ana-
tomical ranges are generally narrower? Is this claim for behavioral
flexibility merely a social hope, or is it good biology as well? Two
different arguments lead me to conclude that wide behavioral
ranges should arise as consequences of the evolution and structural
organization of our brain. Consider, first of all, the probable adap-
tive reasons for evolving such a large brain. Human uniqueness lies
in the flexibility of what our brain can do. What is intelligence, if
not the ability to face problems in an unprogramed (or, as we often
say, creative) manner? If intelligence sets us apart among orga-
nisms, then I think it probable that natural selection acted to max-
imize the flexibility of our behavior. What would be more adaptive
for a learning and thinking animal: genes selected for aggression,
spite, and xenophobia; or selection for learning rules that can gen-
erate aggression in appropriate circumstances and peacefulness in
others?
Secondly, we must be wary of granting too much power to nat-
ural selection by viewing all basic capacities of our brain as direct
adaptations. I do not doubt that natural selection acted in building
our oversized brains—and I am equally confident that our brains
became large as an adaptation for definite roles (probably a com-
plex set of interacting functions). But these assumptions do not
lead to the notion, often uncritically embraced by strict Darwinians,
that all major capacities of the brain must arise as direct products
of natural selection. Our brains are enormously complex com-
puters. If I install a much simpler computer to keep accounts in a
factory, it can also perform many other, more complex tasks unre-
lated to its appointed role. These additional capacities are ineluct-
able consequences of structural design, not direct adaptations. Our
vastly more complex organic computers were also built for reasons,
but possess an almost terrifying array of additional capacities—
including, I suspect, most of what makes us human. Our ancestors