INTELLIGENT DEVELOPMENT 151population densities. Likewise, the sex ratio in certain reptiles is known
to be developmentally plastic. Each embryo develops into a male or a
female depending on local conditions, such as temperature, at the time
(investigators incubating eggs in the laboratory were initially astonished
to fi nd that off spring were either all male or all female). Classic meta-
morphosis in frogs and other amphibians involves the remodeling of al-
most every organ in the body, and radical changes in be hav ior from fi lter
feeder to predator and in locomotion and visual systems.
Not surprisingly, in some cases of developmental plasticity, the diff er-
ences between the morphs have been so stark as to lead them to be clas-
sifi ed as diff er ent species and presumed to have diff er ent genes.
Of course, the most celebrated example of such life- long developmen-
tal plasticity is that in the brain. Canalized development seems to ensure
that neurons in diff er ent layers in the ce re bral cortex— the most recently
evolved aspect of the brain— form the requisite variety of pro cessing
types. Th ese will then be “good enough” for the demanding tasks ahead.
But the wiring up of these into specialized areas, with their specifi c re-
sponse properties, seems to depend on context and experience.
Such plasticity of development has been demonstrated spectacularly
in many ways. Many years ago Mriganka Sur and his colleagues surgically
rerouted visual nerve connections from the eye in newborn ferrets
away from their usual destination in the visual cortex of the brain. Th ey
directed them, instead, to what usually develops as the auditory cortex
(i.e., pro cessing auditory information). Th at auditory cortex subsequently
came to pro cess visual information like an ordinary visual cortex.
Somewhat similarly, it has been shown that plugs of cortex trans-
planted from, say, visual to somatosensory areas (responding to sensa-
tions of touch), develop connections characteristic of their new location
rather than those of their origins. Fi nally, it has been shown how the
functions of one area of the brain, surgically removed, can be taken over
by another.
Developmental plasticity obviously refl ects potential and variation
being created by intelligent systems, rather than from the blind codes in
genes. It will be favored when there is environmental heterogeneity in
space and time. However, the cases considered so far are limited in that
they involve a one- shot developmental trajectory. Development has a
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