Page 263 - Deep Learning

246 Adaptation

and therefore effective instruction, is not much older than the oldest cave
paintings. Our genome has changed little since then, so this line of thought
implies that learning from instruction does not have a genetic basis of its own.
If so, instruction is not an adaptation in the biological sense but a cultural
practice. We might not have any brain structures that evolved in response to
any selective pressure toward learning from instruction. Instead, instruction
works by abetting the operation of learning mechanisms that evolved for unas-
sisted learning. I refer to this as the Piggyback Hypothesis.
Piggyback raises a paradox: If assisted learning makes use of the same
learning mechanisms as unassisted learning, why is it more effective? The
answer must be that instruction makes those mechanisms do more, or dif-
ferent, work. As a didactive example, consider the hypothesis that learning
proceeds, at least sometimes, through generalization. It is widely believed that
we group our experiences on the basis of similarities, extract those similarities
and encode them in general concepts. If our brains are indeed wired to carry
out such a generalization process, then how might instruction help? In the
unassisted mode, the number of general concepts acquired per unit of time
is determined by the density of generalizable events in the stream of expe-
rience. But an instructor can make the generalization mechanism do more
work by arranging events that trigger the formation of a particular concept
within a shorter time period than would have been the case in the natural
sequence of events. A geometry teacher does precisely this when he teaches
the concept equilateral triangle by showing students a series of examples on
the blackboard, such triangles being somewhat scarce in the woods and on
the streets. Although one might question the idea that we form concepts in
precisely this way outside geometry class, the example illustrates how a delib-
erately designed sequence of experiences can abet a cognitive mechanism that
did not evolve to learn from instruction.
This situation is not unique. Consider an analogy to vaccination: Our
immune system did not evolve to create antibodies in response to a shot in
the arm. Nevertheless, by receiving a weak form of a virus before an encoun-
ter with the real thing, the immune system can be boosted to handle an oth-
erwise overwhelming virus attack. Cooking provides a second analogy: The
time since we began to heat our food is too short for there to have been many
genetic changes to our digestive system, so the latter is primarily designed, as
it were, to process raw food. Cooked food nevertheless nourishes us better,
improving health and longevity. Vaccination and cooking are both examples
of Father Artifice helping Mother Nature make the most of biological systems
that evolved before the relevant artifices were invented.