Friendship in Animals: From Chimpanzees to Dolphins

Do Animals Have Friendships?

Yes — and the evidence is growing. Brent et al. (2014) draw on the comprehensive review by Seyfarth and Cheney (2012), which summarizes the increase in documented species. Social bonds have been reliably documented in birds, ungulates, whales, and primates.

Affiliative behaviors include spending time together, vocalization, grooming, cuddling, cooperative foraging, food sharing, and alliance formation. The decisive criterion: friends interact significantly more often and over longer periods than non-friends.

How Is Friendship Defined in Animals?

Following Hinde, Brent et al. define friendship as bidirectional, affiliative (non-aggressive, non-reproductive) interactions whose frequency and consistency distinguish them from non-friendship relationships. This definition deliberately avoids assumptions about emotions or motives.

This is a conscious methodological choice: whether a chimpanzee “feels friendship” cannot be measured directly. But whether it interacts systematically more often with certain conspecifics — that can be measured. And that is precisely what makes the definition useful for cross-species comparisons.

Examples from the Animal Kingdom

The diversity is striking. Here are some of the best-documented cases:

What Sets Human Friendship Apart?

The biggest difference: humans may be unique in the extent of non-kin friendships. In most animal species, close bonds exist primarily between relatives — mother-daughter pairs and siblings dominate.

Humans, by contrast, have many close friends who are not related. Brent et al. attribute this to the scarcity of available kin in early hunter-gatherer groups. Unrelated friends may still be genetically more similar than random strangers — functioning as a kind of “functional kin.”

Humans also possess the cognitive capacities for far more complex friendships: theory of mind, language, cultural norms, and the ability to maintain relationships across great distances.

Non-Kin Friendships

That friendship between non-relatives exists is evolutionarily remarkable. In horses, groups consist of one stallion and several unrelated mares — yet these mares form differentiated affiliative relationships. Lasting bonds between non-kin have also been documented in spotted hyenas.

Comprehensive data are still needed to determine whether animals form friendships with non-kin only when no relatives are available — or whether they actively choose non-kin as friends. What is clear: the biochemical mechanisms behind bonding are the same regardless of kinship.

Limits of the Research

The behavior-based definition avoids emotional criteria, which some researchers criticize as too narrow. Whether friendship is a feature of all species with stable social groups remains unclear. And transferring the concept from animals to humans is methodologically demanding, since human friendships carry additional cultural dimensions.

Frequently Asked Questions

Do animals have real friendships?

Yes. Social bonds equivalent to human friendship have been documented in birds, ungulates, whales, and primates. Brent et al. (2014) define them as bidirectional, affiliative interactions whose frequency and consistency distinguish them from non-friendship relationships.

Which animals form friendships?

Chimpanzees, bonobos, baboons, dolphins, elephants, horses, hyenas, giraffes, red deer, bison, and various bird species. The list keeps growing with more research — the diversity of documented species has expanded considerably over the past decade.

What distinguishes animal friendship from human friendship?

Humans may be unique in the extent of non-kin friendships. In most animal species, close bonds exist primarily between relatives. Humans, by contrast, have many close friends who are not related — likely due to the scarcity of available kin in early hunter-gatherer groups.

Why do animals maintain social bonds?

Because of measurable adaptive benefits: animals with closer social networks show lower cortisol levels, higher reproductive success, and longer survival. Affiliative behaviors such as grooming, cooperative foraging, and alliance formation secure these advantages.