Why do related animals sometimes help raise one another’s young?

Related animals often help raise one another’s young due to a process known as kin selection. This evolutionary theory explains that individuals can increase their genetic success—or inclusive fitness—not only by producing their own offspring but also by assisting in the survival and reproduction of relatives who share their genes.12

When an animal engages in such altruistic behavior, it is often because the indirect fitness benefits gained by helping kin outweigh the costs of the effort or risk involved. This behavior is frequently observed in:1

• Cooperative breeding: In species like certain birds and meerkats, individuals may remain in their natal groups to help raise younger siblings. This often occurs when environmental constraints, such as a shortage of high-quality territories or mates, make it more advantageous to stay and help than to attempt independent reproduction.23
• Eusociality: In highly social insects like honeybees, sterile workers forgo their own reproduction to support the queen. Because of their unique genetic systems, these workers may maximize the propagation of their shared genes by helping to raise sisters rather than producing their own offspring.43

Ultimately, Hamilton’s rule suggests that such aid-giving behavior evolves when the benefit to the relative, multiplied by the degree of genetic relatedness, exceeds the cost to the helper.13