Few animal displays are as alien, yet as touching, as a reunion of  two Laysan albatross mates. Having scoured the oceans alone for months  and thousands of miles, Laysan albatrosses return to the same stretch of  shoreline to mate with the same bird. After clumsily crashing to the  ground and testing their shaky legs that have not touched land for  months, albatrosses go in search of their mate. Miraculously, they  manage to find their partner among the hundreds of other birds packed  into their breeding colony. Once they reunite, the albatross couple  performs a dance to reform their bond. They stand facing one-another,  clacking their beaks, and mimicking each other’s head bobbing. Their  twittering and angular wing displays increase in pace and intensity. At  the crescendo of their hopping and shrieking, they halt, and break down  into a bout of gentle preening and soft embraces in which they copulate.  Their choreographed dance may seem foreign to us, but the sentiment  behind their tender embraces is universally understood.

Albatrosses may not breed successfully until they are eight or nine  years old, but once they settle on a lifelong mate, they will perform  these same rituals every time they meet for the rest of their  60-year-life. Bonded together, the couple will tirelessly raise a single  chick, fighting against the elements and dwindling fish stocks as they  take turns foraging among the endless waves for many days at a time. Do  they think fondly about their life partner tending to their chick as  they glide effortlessly above the stormy seas? It is tempting to  envision their thoughts and see their unyielding devotion to their  partner as romantic. One might even go so far to say their behaviour  looks akin to love. But what is love for an animal? In comparison to our  own complicated relationships, the albatross system may seem  refreshingly simple. They find a mate, stick with them for life, and  raise offspring together. Is that not what traditional Western ideals  tell us we should be doing with our own relationships? So why can’t we  love like an albatross? The short answer is because we are not  albatrosses. Yet, this relatively straightforward idea brings up the  larger issue of why species pair, mate, and raise young differently.  More importantly, it begs the question: are we unique in our own  capacities for intimacy and love?

The difficulty with studying animal relationships like those between  albatross mates is that it is impossible to know how an animal actually  feels. We cannot read their thoughts, nor can we ask them whether they  think fondly of their partner or long for them while they are apart.  Therefore, those who study animal relationships do not refer to  non-human relations in terms of “intimacy” and “love” to avoid  projecting our inherently biased human experience onto minds we do not  fully understand. Instead, what scientists can do more objectively is  investigate the behavioural and physiological changes that take place  during the breeding process. These observations can reveal the patterns  of animal relations and allow us to sometimes extrapolate about the  underlying mental states they produce. Enough research has been done  through these methods to teach us a considerable amount about animal  mating systems and the pair bonds that can unite mates.

Pair bonds result from hormonal changes in the brain. Even in humans,  the deep-seated desire we feel for companionship and intimacy has a  hormonal basis that developed over evolutionary time. Just as species  differ in other biological traits, their hormone levels also differ  greatly to dictate how readily and strongly they form pair bonds. This  means that even closely related species can deal with sex very  differently.

Pair bonds and relationships surrounding reproduction come down to  sex. At a basic level, sexual reproduction inherently involves unequal  investment by males and females. Eggs are more costly to produce, while  sperm is readily abundant and replenishes throughout a male’s lifespan.  Hence, females should be choosy about their partners because they are  giving up a limited resource to reproduce. At every mating, the female  risks squandering her reproductive opportunities with inadequate males  or poor genes. The pressure of female choice gives rise to competition  between males and drives much of the variation seen between males and  females. Pair-bonding, on the other hand, is derived by the need for  parental care. In species whose offspring would not survive without the  continued input of both partners, bonding between the male and female  allows them to better raise their young.

The power of natural selection to produce distinctive traits is no  more evident than in its effect on mating systems. Competition for mates  produces evolutionary pressures that have shaped some of the most  mesmerizing spectacles in the animal kingdom. From haunting male  humpback whale song, to the herculean clashes between sparring male  rams, sexual selection has produced tremendously beautiful animal  displays. But sometimes attracting a partner involves more than just  physical demonstrations of fitness. Natural selection is also  responsible for producing traits that mirror some of the intimacy we  strive for as humans. The cognitive demands of maintaining a strong bond  between partners has made it advantageous for certain species to  anticipate and expect the desires of their mate. Male Eurasian Jays, for  example, can anticipate their partners’ desires and respond, even if  her wants directly conflict with their own.[i]  They routinely share food with their female partners during the  breeding season to reinforce their bonds, and will choose foods to share  with her that they believe she desires, even if they themselves do not  want that type of food. Being able to attribute a desire to another  individual is a cognitive feat rarely seen in the animal kingdom, yet  its existence outside of humans gives credence to the idea that we are  not so different than other animals, even in our pair bonding. While we  do not know whether this type of perspective taking evolved specifically  to foster pair bonds in these birds, having the cognitive wherewithal  to do so would certainly have its advantages in pleasing a partner.

In other species, however, none of this type of cognitive genius is  needed for successful mating. Perhaps one of the most drastic examples  in mammals comes from the elephant seal. Elephant seal males do not pair  with specific females, but instead guard a large stretch of beach that  contains up to a hundred females. As long as they are able to defend the  sands from competing males, they can mate with all females that come  ashore, and need not  invest in their young at all. In fact, as they  barrel along the beach with their three tons of blubber and muscle to  ward off potential competition, they even can crush their own calves.

The diversity of mating systems and pair bond relations that result  from selection pressures is dizzying, yet there are many parallels  between animal systems and our own. Some have such a strong desire for a  bond with another individual that they seek relationships that  transcend reproduction. Homosexual pair bonds are quite normal in many  species.[ii]  In other cases, the dynamics of non-human relationships could easily be  mistaken for the drama of a reality TV show. Fighting between pairs,  and cheating on partners is commonplace in many mating systems. In  humans “cheating” carries the assumption that a partner is being morally  dubious. In animals, however, “extra pair copulations” are a natural  phenomenon that is easily explained in terms of maximizing one’s  reproductive success. Being socially monogamous—i.e. bonding with a  partner to help raise offspring, but still mating with other  partners—allows one to share the burden of parental care but still  obtain genes from a potentially better partner. While human cultures  vary in their tolerance of homosexuality and cheating, they are both  universal features of human relations found throughout the world. Does  this mean animals are more human than we often give them credit, or that  humans are no more than animalistic tendencies shrouded in conceptions  of culture?

Charles Darwin’s oft-quoted theory that “[t]he difference in mind  between man and the higher animals…certainly is one of degree and not of  kind”[iii]  applies to mating systems as accurately as any other cognitively  motivated trait. In questioning our inherent superiority over the forces  of natural selection, we are compelled to accept that we are no  different than any other species in owing our feelings towards a partner  to our evolutionary history. Scrutinizing non-human mating systems may,  therefore, help us better understand ourselves. This idea has motivated  a huge body of literature into the reproductive behaviours of many  species.

In trying to understand our own mating system, it is tempting to look  at our closest relatives. However, primates do not have a consistent  mating strategy and comparison to them leaves us little certainty about  our own system. There are species such as the hamadryas baboon, in which  dominant males defend and mate with a harem of females, traveling in  large groups as they graze the African savannahs. In contrast, female  tamarins, a species of small tropical forest monkey, frequently have two  male partners who help her raise their offspring together. Sex in our  closest relative, the chimpanzee, for instance, is different again. Wild  chimpanzees live in male-dominated social groups and violence between  neighboring groups is frequent.  When females reach reproductive age,  they emigrate from their natal group, but can only leave and join  another while they are reproductively receptive; a state which is  advertised through a large pink swelling that inflates during estrus,  and functions as a “pink passport” to allow them to travel safely to  neighboring groups.[iv] In  contrast, bonobos, the cousin of the chimpanzee, are purported to have a  radically different system in which sex is open, frequent and happens  between all members of a group, including members of the same sex,  juveniles and elders. Bonobos are known for their promiscuity because  they use sex as a way to diffuse tension. The juxtaposition of these two  opposing approaches to sex in our closest relatives has fostered an  existential crisis over whether humans are designed to be violent  war-mongers or free-loving hippies.[v] In  reality, however, idealizing the lifestyle of the “make love, not war”  primate does not get us any closer to understanding our own systems of  love.

The crux of the issue lies in whether we can ascribe morality to  animal sexual systems. By doing so we are inherently projecting our own  human-centric views onto other species systems that we may not  understand. By demonizing chimpanzee violence, we are forgetting that  sex is part of chimpanzee life history that has allowed them to survive  in their tropical forest habitat. In any mating system, sex is the key  to survival. Without it, no sexually reproducing species would pass on  their genes. Therefore, traits that favor successful reproduction are  more likely to persist in the population.

The expression of mating systems, including our own, is not, however,  solely dependent on genes. The environment can play a role too in  influencing patterns of reproduction. In some species, individuals will  employ different mating strategies depending upon their physiological  state. For instance, horseshoe crabs generally secure a mate by clasping  onto her back as she heads to shore so they may copulate on the sand  together. Males that experienced more difficult environmental  conditions, such as being unable to obtain adequate nutrition, will  adopt a strategy of sneaking in on a couple and stealing a copulation  with another crab’s partner. While various types of environmental  variability can provoke different mating strategies, the influence of  the environment is most exaggerated in humans as our cultures dictate  much of how we mate.

As humans, our cultural norms greatly influence our mating choices  and what we expect to gain in terms of intimacy with our partners. We  are similar to other animals, however, in being unable to escape some of  the biological heritage that predisposes us to seek out bonds with  other people. Hence, when studying animal pair bonds, it is endlessly  tempting to compare our own situation to animal models. Wouldn’t life be  easier if we could count on our partner like an albatross can count on  theirs? Equally, there are sure to be many men who wouldn’t mind having  relations like a hamadryas baboon, or many females that wouldn’t mind  trying out the tamarin monkey’s system. However, exalting any animal  system out of context risks glossing over the challenges animals face in  finding mates and raising offspring—challenges that shaped the very  creation of their system. We cannot mate like an albatross, or love like  a bonobo, any more than we can swim like a fish or fly like a bird. We  experience different forces of attraction because we have each evolved  along a unique evolutionary trajectory. We forget that our experience of  love is just as much part of being human as having two legs. Yet at  least we can commiserate in the fact that we are not alone in desiring  the company of others, even if only for a short while, on a distant  shoreline after a long journey home.