The Theory of Inclusive Fitness
If a blackbird's primary instinct is self-preservation, why does it risk death in order to
warn others in the flock that a hawk is approaching? Why does a young man, who has his
whole life ahead of him, jump in front of a speeding bus to save a child? Are these
behaviors spiritually altruistic, or is there some biological explanation for self-sacrifice? The
traditional theory of evolution in the early 1900s proposed the idea of "survival of the
fittest." This idea made evolution seem like a competition between individual creatures, and
it did not explain why animals sometimes make sacrifices to help each other. However, in
1964, W. D. Hamilton proposed the theory of "inclusive fitness," which seems to explain
the mystery of self-sacrifice.
The instinct to protect one's young, or one's family, is easily understandable in terms of
evolution. According to Hamilton, an organism may contribute to its own chances of
passing on its genes if it helps others that share the same or similar genes. This same helpful
behavior can be extended to other, more distantly related members of the same species.
Hamilton's theory of inclusive fitness says that not only do we have an instinct to protect our
own young, but we also have an instinct to protect the reproductive success of others, as
long as they are somewhat related to us.
The theory of inclusive fitness suggests, of course, that the probability of the young
man heroically rescuing the child will decrease as the degree of relatedness between him
and the child decreases. But if the child is his own, the likelihood of him helping is far
greater than if the child is not in his family. This rather disturbing prediction has been
supported by studies of organisms as diverse as ground squirrels and humans alike
Which of the following levels would you be using if you successfully predicted that a
pregnant cat would be willing to adopt an orphaned kitten?
a. Level 2: Understanding
b. Level 3: Applying
c. Level 4: Analyzing
d. Level 5: Evaluating
e. Level 6: Creating
b
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