In mammals and most birds, individuals emerge into the world after a complex ontogenetic history in which behavioral differentiation played as important a role as tissue differentiation.

• 在哺乳类以及大多数的鸟类，个体的出生是经过一个复杂的发育历程，而行为的分化在这个历程中所扮演的角色就像组织分化一样重要。