For most creatures, procreation is an emotionally uncomplicated affair. In humans, however, it has a tricky accomplice: romantic love, capable of catapulting us to bliss or consigning us to utmost despair. Yet capricious though it may seem, love is likely to be an adaptive trait, one that arose early in the evolution of our lineage.
Two of the hallmarks of human evolution—upright walking and large brains—may have favored the emergence of love, according to a theory advanced by anthropologist Helen Fisher of Rutgers University. Bipedalism meant that mothers had to carry their babies, rather than letting them ride on their back. Their hands thus occupied, these moms needed a partner to help provision and protect them and their newborns. Ancient bipedal hominids such as Australopithecus afarensis, the species to which the 3.2-million-year-old Lucy fossil belongs, probably formed only short-term pair bonds of a few years, however—just long enough for the babies to be weaned and walking, after which females were ready to mate anew.
The advent of large brains more than a million years ago extended the duration of these monogamous relationships. As brain size expanded, humans had to make an evolutionary trade-off. Our pelvis, built for bipedalism, places a constraint on the size of a baby’s head at birth. As a result, human babies are born at an earlier stage of development than are other primate infants and have an extended childhood during which they grow and learn. Human ancestors would thus have benefited from forming longer-term pair bonds for the purpose of rearing young.
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Fisher further notes that the ballooning of the hominid brain (and the novel organizational features that accompanied this growth) also provided our forerunners with an extraordinary means of wooing one another—through poetry, music, art and dance. The archaeological record indicates that by 35,000 years ago, humans were engaging in these sorts of behaviors. Which is to say, they were probably just as lovesick as we are.
