Paternal care refers to the time and resources given by a biological father to his offspring. The presence of paternal care varies across human cultures. However, most societies exhibit some degree of paternal care. In some cultures, fathers are only responsible for male children after they reach a certain age, when skills need to be passed on - while in others, fathers may play important roles from children's early ages onward. Paternal care is a behavior found in some Great apes, although there are differences in the extent and quality of care provided. However, the difference in quality of paternal care given by humans versus other primates is absolutely unique.
Paternal care refers to the time and resources given by a biological father to his offspring. Paternal care is a broader category of behavior than related concepts such as paternal investment, with the latter referring to investment by a male in biological offspring at some reproductive fitness cost to himself and reproductive fitness benefit to his offspring. In mammals, less than 5% of species show male investment in parenting. Given how few mammals exhibit this behavior, the extent of paternal care in humans is remarkable.
There are various types of paternal care. In a classic typology of primate paternal care, Kleiman and Malcolm (1981) divided paternal care into direct and indirect forms. Direct care includes forms such as holding and carrying offspring. Indirect care includes forms such as defense, whether against predators or threats from members of the same species, and food provisioning.
How do patterns of human paternal care compare with those among Great Apes? Viewed broadly, the magnitude of human paternal care is a distinguishing characteristic of our species, and one that appears to have been derived during the past couple of million years of hominin evolution. Characterizing more specific forms of paternal care—types of direct care as well as indirect care—these features may have been derived at different time points during recent hominin evolution. We'll consider the evolutionary origins and Great Ape comparisons for features of a) indirect care such as food provisioning and protection, b) direct care such as holding and time spent in proximity to offspring, and c) roles of fathers in offspring social and moral development. This last category does not easily fit the distinction between direct and indirect care applying to comparative patterns of paternal care but is of notable importance too.
Although it would be ideal to consider this behavior in Neandertals or earlier Homo species, the fossil record gives little insight into the extent of paternal care seen in these species. Fossil evidence points to physical male-male competition as an important feature of sexual selection in Australopithecus (LCA: 4,000,000 years), which is a general indicator of a polygynous mating system and lower paternal care (compared to maternal investment). One of the few indicators of change in male-female responsibilities towards offspring is reduced sexual dimorphism. Although men are physically larger, stronger, and have a longer maturational period than women, there is a substantial reduction in relative male physical size from Australopithecus to modern humans. Reduction in sexual dimorphism indicates reduced male-male competition, development of a multi-male multi-female social structure, and a decrease in polygynous matings. These factors, together, suggest a gradual increase in male paternal investment over evolutionary time.
Our closest cousins, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) live in multi-male multi-female fission-fusion communities, in which the females are the primary care-givers and the offspring depend heavily on the mother for a large part of their childhood. Advertised ovulation and promiscuous behavior of females result in reduced paternal involvement and pair bonding.
Rhesus macaques (Macaca mulatta) live in multi-male, multi-female social groups, and both males and females are promiscuous, with no expression of paternal care, except for basic protection. Neither orangutans (Pongo) nor gibbons (Nomascus leucogenys) show paternal care behavior. In orangutans, being a semi-solitary species, males rarely have access to offspring. Although gibbons are a monogamous species with absolute paternity certainty, females are the primary care-givers. This may mean that paternal care evolved within the Homo genus (or at the earliest in Australopithecus).
However, gorillas (Gorilla gorilla) live in single-male harems, which typically include one reproductive male and multiple females who mate with this male. In addition, gorillas have a semi-concealed ovulation, and because of the single-male system, there is almost complete paternity certainty. Adult male gorillas show high levels of affiliation with offspring, and are known to “hold, cuddle, nuzzle, examine and groom infants, who turn to these males in times of distress”. Given the above evidence from non-human primates, it would be, parsimoniously speaking, more probable that the paternal care behavior (as seen in humans) could have developed from a gorilla-like social system.
Anthropologists and other evolutionary biologists have long suggested that the evolutionary origins to human pair bonds and paternal care entailed some version of a “man the hunter” hypothesis. The idea is that during hominin evolution a sexual division of labor, in which men and women performed mostly complementary economic and reproductive tasks, emerged, with males specializing as hunters and women as gatherers and in providing offspring direct care. From the standpoint of paternal care, this type of scenario highlights a presumed deep evolutionary history in hominins of male indirect care in the form of resource provisioning, particularly of meat. This type of scenario enjoyed support from analogies drawn from recently studied hunter-gatherers and archaeological evidence such as stone tool cut marks on presumed prey bones as well as postulated meat-processing benefits derived from stone tool traditions tracing back 2.6 million years.
However, others have challenged such “Man the Hunter” scenarios on various grounds. One contention is that in hunter-gatherer societies men tend to focus on large game for purposes of showing off or costly signaling rather than for purposes of provisioning one’s wife and offspring. There is support for the view that among hunter-gatherer societies some of men’s provisioning efforts have wider social benefits than family provisioning, with enhanced male status perhaps translating into reproductive fitness benefits. However, there is also evidence—such as men targeting resources such as small game and honey that disproportionately flow to their wives and offspring, and men providing more resources to biological offspring than stepoffspring—that is consistent with provisioning.
More full consideration of potential human paternal care in the form of paternal provisioning entails several other issues. The history of hunting technology innovation, with spears first found approximately 400,000 years ago, and bows and arrows around 30,000 years ago, means that hominin male hunting efficiency in the past was likely much lower than that observed among recently studied foragers. Furthermore, a major feature of human reproduction is that hunter-gatherers interbirth intervals (time between successive births) of approximately 3-4 years are considerably lower than would be expected for an ape of our body size. Orangutan interbirth intervals in the wild are approximately 8 years, the longest of any terrestrial mammal, whereas interbirth intervals of chimpanzees and gorillas in the wild tend to be around 4-6 years. A combination of enhanced hominin female foraging efficiency (e.g., through use of technologies such as digging sticks) and food provisioning by other group members such as grandmothers and husbands enables humans to reproduce at faster rates—the lower interbirth intervals—than would otherwise be expected. To the degree husbands contribute to these reductions in interbirth intervals, the main benefit of paternal provisioning may be in facilitating faster reproductive rates rather than having impacts on offspring survival. There is no good analogy or homology for paternal food provisioning among Great Apes, indicating that whatever the evolutionary timing of its origin among hominins, and cautious over the mixed role of paternal care/costly signaling, this is a derived feature of humans.
Apart from food provisioning and “Man the Hunter” scenarios, human indirect paternal care could entail protective services. Considerable attention has been given to the potential role of infanticide prevention as an indirect form of paternal care among primates. Among Great Apes, an interpretation that gorilla male infanticide protection services seems consistent with the attribution of infant mortality to infanticide among a fair number of cases, and apparent role fulfilled by males of offspring defense against potential male group intruders. Among humans, infanticide prevention as an indirect form of paternal care among recently studied hunter-gatherers or across a wider array of contemporary societies does not seem well supported: while stepfather presence is associated with elevated offspring mortality and abuse risk in various studies, these cases are relatively rare and seem incidental to low male emotional attachment rather than adaptive reproductive strategies.
An additional potential form of indirect human paternal care is defense against predators. While relatively few hunter-gatherers die at the maws of predators such as leopards or large bears, it is reasonable to imagine that male protective services help account for some of this reduction in mortality, but also difficult to quantify this potential form of indirect paternal care.
Another form of indirect paternal care—passing along non-food material resources such as land or livestock—seems to have been derived recently in human history, consistent with the expanded array of forms of heritable wealth. Fathers may help their sons marry by providing resources such as livestock or land to serve as bridewealth in many societies. Fathers may leave an inheritance upon death consisting of money, a house, land, or other such material resources; often these are left with a spouse, with benefits further extended to offspring, making this also a form of indirect paternal care. Since accumulations of wealth of these sorts would only extend to some fairly recent complex hunter-gatherers and other societies relying on non-forager subsistence modes, these don’t project far in evolutionary history, and have no apparent analogy or homology among Great Apes.
As far as forms of direct paternal care, these can be assessed in various ways. Through studies of time allocation among hunter-gatherers such as the Hadza and Aka, scholars have helped clarify the amount of time fathers spend with their children primarily during waking hours, but also in some cases forms of direct care such as holding or carrying. Hunter-gather fathers, with the main exception of the Aka, spend a relatively small fraction of their waking hours in direct contact care of their young offspring, or even in close proximity. Part of that pattern seems related to the sexual division of labor, in which husbands and wives are often spatially segregated across the day, focused on different economic and social activities. Other caregivers such as mothers, primarily, but also grandmothers and other female relatives including older sisters play important roles in direct childcare. At nighttime, hunter-gatherer fathers tend to sleep in close proximity to a wife and their young children, providing additional time to tend to form attachments with their offspring. It is noteworthy that hunter-gatherer fathers tend to spend more time in direct care of children than is true of many agricultural and pastoralist societies, in part a reflection of greater polygyny among such latter societies which comes at expense to direct paternal care.
A final, possibly uniquely human, feature of paternal care is that related to offspring social or moral development. Fathers can contribute to their offspring’s social success by facilitating their children’s incorporation into beneficial social networks and fostering the development of beliefs and behaviors that yield reproductive success in the local environment (e.g., practice at being a good hunter or honey collector, with later social and reproductive rewards to follow). These types of paternal care often entail mostly modeling rather than teaching in hunter-gatherers or other small-scale societies, and are often sex-specific, with fathers tending to spend more time with their sons than daughters during their children’s late childhood and adolescence. The nature of father-son interactions tends to involve fewer conflicts in hunter-gatherers, probably in part because of a lack of heritable forms of wealth, compared with agriculturalists, pastoralists, and other kinds of societies.
Most human populations have some form of paternal care. Given how incapable human infants are of taking care of themselves for a large part of their early life up until adulthood, contribution from the male parent towards direct care became increasingly important for offspring success. However, some cultures exist where male parents seldom have contact with their offspring, and the female parent is the sole caregiver. One example is the Eyasi Datoga community in northern Tanzania, a patrilineal, patriarchal pastoralist society with a warrior tradition. Close to 40% of Datoga families are polygynous, men spend much of their day away from their homesteads, and have minimal interaction with infants. Men sometimes interact with older children who help tend herd animals, but believe that caring for infants is “women's work”.
Geary and colleagues propose that the human social structure (and hence bi-parental care as the primary form of parental care) could have evolved from a gorilla-like community system (described above). For this kind of system to have evolved, several behavioral traits would have to develop from the gorilla social structure, including:
(a) reduction in male-male aggression and formation of kin-based coalitions.
(b) development of concealed ovulation (as opposed to semi-concealed ovulation seen in gorillas), increasing the duration of time a male spends with a female for assured reproduction and paternity.
(c) strengthening of the male-female pair bond, increasing the benefit of staying with the current mate over seeking new mates
A number of mechanisms have been suggested to explain human paternal care (described below), however, extensive work is needed to show clear differences in humans and primates.
(a) Brain functional processes: Imaging studies identify several areas in the brain that activate in response to infant-related stimuli including the hippocampal formation, anterior cingulate cortex, amygdala, insula, orbitofrontal cortex, and ventral prefrontal cortex. These regions allow humans to attach emotion to infant-parent interaction, store this in the long term memory for later distinguishing between one's own infant and another's, and stimulate increased reward and emotional arousal in response to infant stimuli. Unique development, activity, and connectivity of these regions could underlie the expression of extensive paternal care in humans.
(b) Neurochemical processes: The neurotransmitters dopamine and serotonin are involved in paternal care circuitry. Dopamine plays a role in both motivation and reward systems, while serotonin is involved in oxytocin release and pair bonding in both sexes.
(c) Neuroendocrinological processes: Testosterone, the principle male sex hormone, varies with social context such as increasing in reproductive contexts and decreasing when long-term bonds and paternal care emerge. Cortisol and prolactin may be important for effective paternal behavior, as well as oxytocin, known to mediate quality of father-infant interaction. However, variations in hormone levels are not causal in paternal behavior, which depends more on environmental and social stimuli.
(d) Genetic processes: The gene encoding the Vasopressin receptor 1a (AvpR1a) is associated with pair bonding and indirectly with paternal care. Polymorphisms in the AVPR1A promoter region alter the density of receptors in brain tissue and possibly changing expression of father care.
In combination, these factors could mediate the paternal care behavior in humans.
There are multiple theories to explain why males would heavily invest in direct care for offspring. In general, as brain size grew larger in humans, it became increasingly difficult for the infant to complete a reasonable level of development in utero, thus possibly leading to infant helplessness at birth. This demanded higher paternal involvement during pregnancy and early infanthood since maternal foraging abilities were greatly compromised during these times. This association created stronger pair bonding and improved the odds of repeated mating. The development of completely concealed ovulation resulted in increased paternity certainty. Paternal care also resulted in more offspring, since help from the male parent relieved the female from complete responsibility for the previous offspring. Finally, these developments must be considered in combination with other concurrent developments such as alloparenting, grandmothering, kinship, and reduction of male-male aggression, which allowed formation of larger social groups.
Human paternal care is a defining, derived characteristic. The specific forms of paternal care—direct, indirect, fostering social development—may have different evolutionary origins, but collectively stand out compared with Great Apes.
Paternal care is seen in several other organisms and is believed to have evolved independently. Examples of species that exhibit paternal care include:
(a) Arthropods such as giant water bugs, sea spiders, leaf-footed bugs, assassin bugs, phlaeothripid thrips, Iporangaia pustulosa and Andrognathidae millipedes show exclusive paternal care, while several crustacean males provide care by building and defending burrows/nest sites.
(b) Fish species including seahorses and jawfish exhibit extensive paternal care.
(c) Rodents including Prairie voles, Campbell's dwarf hamster, the Mongolian gerbil, the African striped mouse and the California mouse exhibit paternal care.
(d) Birds: Fathers contribute to parental care in 90% of the bird species, and is believed to be an ancestral trait that evolved before and was necessary for the evolution of flight.
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