Evolution of Biparental Care in Humans

This entry was written by Sarah Partridge as part of a project done in BIAN 2133 ‘Human Reproductive
Strategies’ at The Australian National University in 2019 Semester 2.


Species that share duties of bringing up offspring are rare, but more common in monogamous groups. Animals have different levels of parental behaviour based upon constraints of reproduction and socioecology, but most mammalian females uniparent (Bales, 2017). Biparental care is a parenting strategy that involves offspring receiving care from both parents. It evolved due to its potential to increase the fitness of offspring and the mother’s ability to invest in future offspring. It occurs when there are benefits to offspring survival and fitness for receiving care from more than one parent, or if costs of seeking out other mates is too high. The care and investment parents make in their offspring to increase the offspring’s chance of survival, is at the cost of their own investment in other or future offspring (Gangestad and Simpson, 2000).

This entry explores biparental care in mammals and primates, and how it may have evolved in humans, with the help of hormones and paleontological evidence, despite contradiction to commonalities about parental care in polygynous species.

Main Body

Biparental Care

Mating and parenting strategies women use depends on their environments. Difficult environments demand biparental care and result in women looking more at investment potential of mates over indicators of genetic fitness. But if the environment was prevalent with pathogens, finding mates with better genetic fitness are emphasised over investment potential (Gangestad and Simpson, 2000).

Mammalian mothers have limited time and resources to invest in current and future offspring and thus must balance between offspring mortality and their own fertility, which influences how long they will provide care (Kramer and Otarola-Castillio, 2015). Female mammals are predisposed to providing more care to offspring than males because eggs are more costly to produce than sperm; gestation and lactation are staples, energetically expensive, and limit future offspring investment; and internal fertilisation secures their maternal certainty (Bales, 2017).

Mammalian males have a trade-off between parental care and investment, and mating opportunities. Males providing care can create benefits that include increases in quantity and quality of offspring, increased offspring survival, and faster developing offspring, but they are only going to provide care if the benefits outweigh the costs (i.e. lost mating opportunities) (Stockley and Hobson, 2016).


Humans wean infants at younger ages, have shorter birth intervals, raise multiple offspring at a time, and have longer periods of dependency than other primates (Kramer and Otarola-Castillio, 2015). These traits likely derived since the last common ancestor during hominin evolution around the Pleistocene era and have had direct effects on parental care. This is constructed upon early human ancestors having longer birth intervals, offspring that reached independence after weaning, and offspring that foraged self-sufficiently. Using paleontological evidence and lactase decline in adults, it can be estimated that ancestor weaning ages were later (like apes: 4-6 years), before it declined to 2-3 years in modern humans. This, along with self-sufficiency of apes and early human juveniles, suggests that there must have been selection for a longer dependence period in hominin evolution, which may have demanded more parental care. Raising offspring of different ages could be associated with the evolution of biparental care because the costs involved with children increase when birth intervals are short and the dependency of offspring is long, and considering humans experience both, it is too costly if the mother does not have help (Kramer and Otarola-Castillio, 2015).

Stockley and Hobson (2016) suggest that paternal care stabilised monogamy and has therefore coevolved with the number of offspring produced and Bales (2017) suggests that biparental care coevolved with monogamy to increase offspring survival or gain future mating opportunities. Humans are mostly polygynous, and observation typically find polygynous species do not provide much male care, but men of many cultures provide some degree of care. Therefore, suggestions that biparental care has coevolved with monogamy cannot be the only influence; it is possible that biparental care evolved independently of monogamy to directly increase fitness of their offspring, thereby creating evolutionary benefits (Gangestad and Simpson, 2000).

Research by Fernandez-Duque and Mendoza (2009) suggested that the evolution of biparental care could be a by-product of parental care evolution, where biparental care was required to successfully raise offspring. The extra care provided by males helps reduce metabolic costs to the mother, allowing her to use energy elsewhere. They also suggested that relationships between evolution of parental care and pair-bonds can form. For this they cross-culturally compared studies on men of Xhosa, South Africa done by Anderson and men of Hadza, Tanzania by Marlowe. Xhosa men invested the more in their biological children and significantly less in stepchildren of former relationships, but stepchildren in current relationships were provided similar care to biological children. Whereas biological children of Hadza had more investment than stepchildren ever did. This behaviour suggests that cultures differ in effort they put into unrelated offspring, a strategy if used right, can woo the mother, especially in cultures like Xhosa. This care could suggest they are good fathers, convincing the mother that he could be a future mate.

Role of Hormones

Hormones could play a huge role in biparental care in humans. High levels of oxytocin during pregnancy and postpartum are associated with attachment and synchronicity in females (Gordon et al., 2017). In fathering, the exposure of fathers to infants and pregnant or lactating females can alter oxytocin levels non-human primates and is a marker of social engagement supporting father-infant bonding in humans.

Gordon et al., (2017) hypothesised that testosterone has inhibitory effects on parental care due to its decrease being associated with fathering. In bi-parental primates, decreasing levels of testosterone were associated with fathers exposed to the scent of offspring. In addition to this, cross cultural studies determined human fathers with lower levels of testosterone were considered more sympathetic and motivated to respond to cries of their offspring, as opposed to males with higher testosterone levels. In mothers, testosterone levels increase during pregnancy could result in increased responses to offspring cries. These hormones might allow for the increase of parental care in humans.


Biparental care in humans is interesting from an evolutionary perspective because of consistent presence of male care across cultures despite the commonality of polygyny over monogamy. Its evolution has been influenced by practices and sociality of varying cultures, hormones, and efforts towards increasing fitness of offspring to simultaneously allow mothers to invest energy elsewhere. These aspects suggest that in many human societies, biparental care has outweighed costs.


Bales K., (2017), Parenting in Animals. Current opinion in psychology, 15, 93-98

Fernandez-Duque E., Valeggia C., Mendoza S., (2009), The Biology of Paternal Care in Human and Non-human Primates. Annual Review of Anthropology, 38, 115-130

Gangestad S., Simpson J., (2000), The evolution of human mating: trade-offs and strategic pluralism. Behavioural and Brain Sciences, 23, 573-644

Gordon I., Pratt M., Bergunde K., Zagoory-Sharon O., Feldman R., (2017), Testosterone, oxytocin, and the development of human parental care. Hormones and Behaviour, 93, 184-192

Kramer K., Otarola-Castillio E., (2015), When mothers need others: The impact of hominin life history evolution on cooperative breeding. Journal of Human Evolution, 84, 16-24

Stockley P., Hobson L., (2016), Paternal care and litter size coevolution in mammals. Proceedings Biological Sciences, 283(1829)

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