Acorn woodpeckers (Melanerpes formicivorus) stash acorns in...

Acorn woodpeckers (Melanerpes formicivorus) stash acorns in storage holes they drill in trees. When these woodpeckers breed, the offspring from previous years often help with parental duties. Activities of these nonbreeding helpers include incubating eggs and defending stashed acorns. What are some questions about the proximate and ultimate causation of these behaviors that a behavioral biologist might ask?

Key Concepts

Kin Selection

Kin selection is the process by which behaviors that help close relatives are favored by natural selection, even at a personal cost. It explains the evolution of altruistic behaviors, such as helpers defending valuable resources or caring for the offspring of kin, as a strategy to enhance the overall genetic success of closely related individuals.

Cooperative Breeding

Cooperative breeding is a social system in which individuals provide care for offspring that are not their own, often involving nonbreeding helpers. This concept is central to understanding how and why individuals in a species work together in rearing young, balancing both immediate caregiving needs and long-term evolutionary benefits.

Inclusive Fitness

Inclusive fitness is an evolutionary concept that expands the idea of individual fitness by incorporating the reproductive success of related individuals. It explains how behaviors that aid relatives can be selected for, as cooperating with kin increases the probability that shared genes are passed on to future generations.

Proximate Causation

This concept refers to the immediate factors that drive a behavior. It involves studying the physiological, neurological, hormonal, and environmental triggers that directly elicit behavior in an individual. For example, a biologist might ask what neural circuits or hormonal changes activate the helpers’ incubation or antistashing behaviors.

Ultimate Causation

Ultimate causation addresses the evolutionary 'why' of behavior, examining how a particular behavior may have been favored by natural selection. Researchers might explore how helping behavior increases overall gene propagation, benefits survival, and enhances reproductive success, even when the helper itself is not directly reproducing.

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