Sigmund Freud once expressed his view that family members are the first and most powerful objects of sexual desire. However, a recent study indicates that biological evolution favored the recognition of siblings within a family unit, thus enhancing altruism towards those individuals and naturally preventing incest.

Fundamental theories in evolutionary biology have long proposed that biological kinship is the foundation of the family unit. It not only creates the sense of altruism that exists among genetically related family members, but also establishes boundaries regarding sexual relations within the nuclear family. Questions have persisted, however, regarding the means by which humans recognize family members – particularly siblings – as close genetic relatives.

Source: Science Daily