Are Friends Genetically Related? What DNA Reveals About Friendship

Are Friends Genetically Related?

Christakis and Fowler (2014) analyzed genome-wide data from the Framingham Heart Study. They compared the genetic relatedness of 1,367 friend pairs with randomly paired strangers. The result: friends show a significantly higher relatedness coefficient than strangers ( +0.0014; p < 2 × 10⁻¹⁶).

This difference is roughly equivalent to the degree of relatedness of fourth cousins. It is small, but statistically robust across the entire genome. From these correlations, a genetic “friendship score” could be calculated that predicted in an independent sample whether two people were friends.

Which Genes Are Involved?

The pattern is not uniform. Compared to strangers, friends display both genetic homophily (similarity) and heterophily (targeted difference).

Homophily concentrates especially on genes for olfactory signaling— friends tend to share similar scent-perception genes. Heterophily shows up more strongly in immune system genes: friends differ in their immune functions.

Both patterns make evolutionary sense. Similar scent preferences could draw friends to similar environments — through food preferences or favored hangout spots. Complementary immune defenses could give the group a collective survival advantage.

Scent Genes and Friend Selection

Olfactory homophily is the most surprising finding. Smell is a sense that often operates unconsciously — we smell similarly, enjoy similar scents, and are drawn to similar environments.

This fits a broader picture: the homophily documented in friendship research has a biological component that goes beyond conscious preferences and social opportunity structures. We choose friends not only by shared interests or values but partly also by genetic similarity — without knowing it.

Functional Kinship

From a comparative perspective, Brent et al. (2014) confirm that kinship preferences in animal friendships are widespread across species. Unrelated friends may serve as “functional kin” with similar genotypes.

Humans may be unique in the extent of non-kin friendships — driven by the scarcity of available relatives in hunter-gatherer groups. But even these unrelated friends are genetically more similar than random strangers. The evolutionary basis of friend selection runs deeper than previously assumed.

Limitations of the Study

The study is based on a single population of European descent from Massachusetts. A fully independent replication dataset does not exist. The genetic friendship score explains only 1.4%of the variance — genes are a measurable but small factor alongside social, psychological, and structural influences.

The specific mechanisms through which genetic similarity influences friend choice remain unclear. The olfactory hypothesis is plausible but unproven. What the study clearly shows: friend selection has a biological component — even if it explains only a small piece of the puzzle.

Frequently Asked Questions

Are friends genetically similar?

Yes. Christakis and Fowler (2014) showed using genome-wide data from 1,932 individuals that friends display a significantly higher relatedness coefficient than strangers. The difference is roughly equivalent to the degree of relatedness of fourth cousins.

Which genes influence friend selection?

Genes involved in olfactory signaling show particular homophily — friends tend to share similar scent-perception genes. By contrast, immune system genes show heterophily: friends differ, which could provide the group with broader pathogen protection.

What does functional kinship mean?

Unrelated friends may serve as “functional kin” — they are genetically more similar than random strangers and fulfill social functions typically reserved for relatives. This places the Christakis-Fowler findings in an evolutionary framework.

Do we choose friends unconsciously based on genes?

Possibly. Similar scent genes could draw friends to similar environments — through food preferences, favored hangout spots, or shared aesthetic tastes. The precise mechanism, however, remains unclear.