How the Mind Works - michaeljgoodnight.com

Revenge of the Nerds 191
WHY US?
Why did some miocene ape first enter the cognitive niche? Why not a
groundhog, or a catfish, or a tapeworm? It only happened once, so no
one knows. But I would guess that our ancestors had four traits that
made it especially easy and worth their while to evolve better powers of
causal reasoning.
First, primates are visual animals. In monkeys such as the rhesus
macaque, half the brain is dedicated to sight. Stereoscopic vision, the
use of differences in the vantage points of the two eyes to give a sense of
depth, developed early in the primate lineage, allowing early nocturnal
primates to move among treacherous fine branches and to grab insects
with their hands. Color vision accompanied the switch of the ancestors
of monkeys and apes to the day shift and their new taste for fruits, which
advertise their ripeness with gaudy hues.
Why would the vision thing make such a difference? Depth perception
defines a three-dimensional space filled with movable solid objects.
Color makes objects pop out from their backgrounds, and gives us a sensation
that corresponds to the stuff an object is made of, distinct from
our perception of the shape of the stuff. Together they have pushed the
primate brain into splitting the flow of visual information into two
streams: a "what" system, for objects and their shapes and compositions,
and a "where" system, for their locations and motions. It can't be a coincidence
that the human mind grasps the world—even the most abstract,
ethereal concepts—as a space filled with movable things and stuff (see
Chapters 4 and 5). We say that John went from being sick to being well,
even if he didn't move an inch; he could have been in bed the whole
time. Mary can give him many pieces of advice, even if they merely talked
on the phone and nothing changed hands. Even scientists, when they try
to grasp abstract mathematical relationships, plot them in graphs that
show them as two- and three-dimensional shapes. Our capacity for
abstract thought has co-opted the coordinate system and inventory of
objects made available by a well-developed visual system.
It is harder to see how a standard mammal could have moved in that
direction. Most mammals hug the ground sniffing the rich chemical
tracks and trails left behind by other living things. Anyone who has