Biology
Kin Selection and Alarm Calling in Belding's Ground Squirrels
Quick fact
Female Belding's ground squirrels give alarm calls more often than males, and they are the ones who live near their female relatives—supporting kin selection because calling helps protect kin who share their genes.
Why this is interesting
When a hawk soars overhead, a Belding's ground squirrel may let out a piercing alarm call—but in doing so, it draws attention to itself and increases its own risk of being eaten. Why would an animal sacrifice its own safety for others?
Read the full explanation
Understanding Kin Selection and Alarm Calling in Belding's Ground Squirrels
Belding's ground squirrels live in colonies where females typically stay close to their birthplace, while males disperse further away. When a predator like a weasel or hawk appears, a squirrel that spots it may give a loud alarm call. This call warns other squirrels to run for cover, but it also makes the caller more visible and vulnerable. This appears altruistic—the behavior is costly to the caller but benefits the group. Evolution by natural selection favors traits that increase an individual's reproductive success. Yet alarm calling seems to reduce survival. The puzzle is resolved by considering that the squirrels are often surrounded by their relatives—especially females, who share a high proportion of genes through common descent. By warning them, the caller is protecting relatives who carry copies of the same genes, including the genes that encourage alarm calling itself. Thus, the behavior can be favored even if the caller's own survival is at risk, because the lives of many relatives may be saved, and those relatives will pass on their shared genes.
A deeper explanation
The mechanism is kin selection, first formalized by W.D. Hamilton. Hamilton's rule states that an altruistic act can evolve if the cost to the actor (C) is less than the benefit to the recipient (B) multiplied by the coefficient of relatedness (r) between them: rB C. Relatedness is the probability that a specific allele in the actor is also present in the recipient due to common ancestry. For ground squirrels, sisters share on average 50% of their alleles (r = 0.5), so if an alarm call saves several sisters, the benefit to those sisters' genes easily outweighs the risk to the caller. Field studies on Belding's ground squirrels have confirmed these predictions. Playback experiments show that squirrels react more strongly to alarm calls from kin than from non-kin. Furthermore, females, who remain near kin, call more than males, who disperse away from relatives. When a squirrel gives an alarm call, it increases the survival of its kin, thereby perpetuating the alleles that contribute to the calling behavior. This explains why alarm calling persists in the population despite its apparent self-sacrifice. This mechanism matters because it reveals a deeper principle: natural selection acts on genes, not just individuals. An individual's fitness includes both its own reproductive success and the reproductive success of individuals who share its genes. Thus, altruistic behaviors that seem paradoxically self-destructive can be understood as an extension of evolutionary self-interest, shaped by inclusive fitness.