The branch of science that is concerned with the study of the nervous system, especially the brain, is called:

neuroscience

Explanation:

Irritability in animals is brought about by the nervous system. the nervous system consists of peripheral nerves and a ventral nerve cord. The nerve fibres are concentrated to form cerebral ganglia acting as a brain for effective co-ordination.

The central nervous system is composed of the brain, spinal cord and their associated nerves. The branch of biology that deals with the nervous system is called neuroscience.

from the original order (top to bottom) the new order will go

1 (founder)

4 (hawk)

2 (mutate)

3 (next generation)

thinking it would be physical characteristics