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FIGURE 10.22 Genetic sex of brain determines the pattern of differentiation in the zebra finch. A. a zebra
finch gynandromorph with male plumage on one side (left) and female plumage on the other side (right). B.
The W chromosome is found normally only in females. The brain section shows in situ hybridization of
mRNA encoding the W chromosome gene, ASW , to be ubiquitous on the female (right) side of the brain, but
virtually absent on the male (left) side (dark areas show label). C. Histological sections of the gonads reveal
dysmorphic testis on the genetically male side (left) and ovarian tissue containing a number of follicles on
the female side (right). D. The HVC nucleus is normally larger in males than in females. The series of images
shows in situ hybridization for androgen receptor mRNA (dark areas) to mark HVC at 3 caudal to rostral
levels. The HVC is 82% larger on the male side of the brain (left) as compared to the female side (right). (From
Agate et al., 2003)
The development of learning may also require a
certain amount of practice, similar to many sensory
and motor skills. For example, many animals build up
a supply of provisions by hiding food in different loca-
tions. Of course, their spatial memory for the hiding
places is crucial if they are to enjoy the fruits of their
labor. When marsh tits are reared in captivity, they will
continue to hide the sunflower seeds that they are fed.
However, if the birds are given powdered seeds that
cannot be stored, they develop a smaller hippocampus
(Clayton and Krebs, 1994). Thus, learning and memory
skills require practice, and this process may influence
nervous system development. Since our immediate
goal is to relate nervous system development to behav-
ior, the following discussion focuses on reasonably
simple forms of learning and procedural memory.
Many vertebrates are born with an ability to obtain
food and warmth from their mother, when offered.
Nestling herring gulls peck at the tip of their mother's
beak for food, neonatal rodents assume a specific posi-
tion in order to suckle at a nipple, and newly hatched
jewel fish have a natural tendency to approach objects
that are colored like the broody adult. Although these
innate motor behaviors are very sophisticated in the
apparent absence of any experience, many animals
learn to recognize and respond selectively to their
mother (Lorenz, 1937). Konrad Lorenz, a co-recipient
of the 1973 Nobel Prize, made the rather dramatic
observation that hatchling ducks and geese will follow
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