Parental care, by males or females, is presumed to increase growth rates, quality, and/or survival of young, and hence ultimately increase the inclusive fitness of parents. In a variety of vertebrate species (e.g., ~80 of birds and ~6% of mammals, both males and females invest heavily in their offspring. Many of these biparental species are socially monogamous, so individuals remain with their mate for at least one breeding season.
- 1 Mammals
- 2 Birds
- 3 Squamates (lizards and snakes)
- 4 Fish
- 5 Arthropods
- 6 Theoretical models of the evolution of paternal care
- 7 Consequences of paternal care for offspring survival and development
- 8 Proximate mechanisms of paternal care
- 9 See also
- 10 References
- 11 Further reading
- 12 External links
Female mammals invest heavily in reproduction, in large part due to lactation. Because these costs are obvious, the physiological costs of female reproductive effort (defined as that proportion of the total energy budget of an organism that is devoted to reproductive processes), especially care of offspring, have been studied extensively in mammals. These costs have been found to include reductions in longevity and in such processes as thermogenesis, physical activity, and immune function, apparently reflecting the high energetic and nutritional demands of parenting.
Male mammals may also invest heavily in reproduction through efforts to enhance reproductive success (e.g., courtship displays, intrasexual combat) or to provide paternal care. However, the costs of paternal care have rarely been studied in mammals, in large part because only 5-10% of mammals exhibit such care. Nonetheless, in those species in which males do provide extensive care for their offspring (i.e., biparental species, including humans), indirect evidence suggests that its costs can be substantial. For example, mammalian fathers that care for their young may undergo systematic changes in body mass and in circulating or excreted concentrations of a number of hormones (e.g., androgens, glucocorticoids, leptin) as a function of reproductive status, and several of these hormones have important effects on body composition, metabolism, and organismal performance. Nonetheless, the energetic and performance consequences of male parental investment have not been investigated directly in mammals.
Human cultures and societies vary widely in the expression of paternal care. Some cultures recognize paternal care via celebration of Father's Day. According to CARTA , human paternal care is a derived characteristic (evolved in humans or our recent ancestors) and one of the defining characteristics of Homo sapiens. Different aspects of human paternal care (direct, indirect, fostering social or moral development) may have evolved at different points in our history, and together they form a unique suite of behaviors as compared with the Great Apes. One study of humans has found evidence suggesting a possible evolutionary trade-off between mating success and parenting involvement; specifically, fathers with smaller testes tend to be more involved in care of their children.
Research on the effects of paternal care on human happiness have yielded conflicting results. However, one recent study concluded that fathers generally report higher levels of happiness, positive emotion, and meaning in life as compared with non-fathers.
According to the United States Census Bureau, approximately one third of children in the U.S. grow up without their biological father in their home. Numerous studies have documented negative consequences of being raised in a home that lacks a father, including increased likelihood of living in poverty, having behavioral problems, committing crimes, spending time in prison, abusing drugs or alcohol, becoming obese, and dropping out of school.
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Paternal care is rare in non-human primates.
Several species of rodents have been studied as models of paternal care, including Prairie voles (Microtus ochrogaster), Campbell's dwarf hamster, the Mongolian gerbil, and the African striped mouse. The California mouse (Peromyscus californicus) is a monogamous rodent that exhibits extensive and essential paternal care, and hence has been studied as a model organism for this phenomenon.
Fathers contribute to the care of offspring in as many as 90% of bird species, sometimes including incubating the eggs. Most paternal care is associated with biparental care in socially monogamous mating systems (about 81% of species), but in approximately 1% of species, fathers provide all care after eggs are laid. The unusually high incidence of paternal care in birds compared to other vertebrate taxa is often assumed to stem from the extensive resource requirements for production of flight-capable offspring. By contrast, in bats (the other extant flying vertebrate lineage), care of offspring is provided by females (although males may help guard pups in some species). In contrast to the large clutch sizes found in many bird species with biparental care, bats typically produce single offspring, which may be a limitation related to lack of male help. It has been suggested, though not without controversy, that paternal care is the ancestral form of parental care in birds.
Squamates (lizards and snakes)
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Paternal care is rare in arthropods, but occurs in some species, including the giant water bug and the arachnid Iporangaia pustulosa, a harvestman. In several species of crustaceans, males provide care of offspring by building and defending burrows or other nest sites. Exclusive paternal care, where males provide the sole investment after egg-laying, is the rarest form, and is known in only 13 taxa: giant water bugs, sea spiders, two genera of leaf-footed bugs, two genera of assassin bugs, three genera of phlaeothripid thrips, three genera of harvestmen, and in millipedes of the family Andrognathidae.
Theoretical models of the evolution of paternal care
Mathematical models related to the Prisoner's Dilemma suggest that when female reproductive costs are higher than male reproductive costs, males cooperate with females even when they do not reciprocate. In this view, paternal care is an evolutionary achievement that compensates for the higher energy demands that reproduction typically involves for mothers.
Other models suggest that basic life-history differences between males and females are adequate to explain the evolutionary origins of maternal, paternal, and bi-parental care. Specifically, paternal care is more likely if male adult mortality is high, and maternal care is more likely to evolve if female adult mortality is high. Basic life-history differences between the sexes can also cause evolutionary transitions among different sex-specific patterns of parental care.
Consequences of paternal care for offspring survival and development
Care by fathers can have important consequences for survival and development of offspring in both humans and other species. A study discovered an extended duration of paternal care in the Gentoo penguin, when compared to other Pygoscelis species. It was found that their fledging period, the time between a chick’s first trip to sea and its absolute independence from the group, was longer than other penguins of the same genus. They hypothesized that this was because it allowed chicks to better develop their foraging skills before becoming completely independent from their parents. By doing so, a chick may have a higher chance of survival and increase the population’s overall fitness. 
Proximate mechanisms of paternal care
The proximate mechanisms of paternal care are not well understood for any organism. In vertebrates, at the level of hormonal control, vasopressin apparently underlies the neurochemical basis of paternal care; prolactin and testosterone may also be involved. As with other behaviors that affect Darwinian fitness, reward pathways in the brain may reinforce the expression of paternal care and may be involved in the formation of attachment bonds.
The mechanisms that underlie the onset of parental behaviors in female mammals have been characterized in a variety of species. In mammals, females undergo endocrine changes during gestation and lactation that "prime" mothers to respond maternally towards their offspring.
Paternal males do not undergo these same hormonal changes and so the proximate causes of the onset of parental behaviors must differ from those in females. There is little consensus regarding the processes by which mammalian males begin to express parental behaviors. In humans, evidence ties oxytocin to sensitive care-giving in both women and men, and with affectionate infant contact in women and stimulatory infant contact in men. In contrast, testosterone decreases in men who become involved fathers and testosterone may interfere with aspects of paternal care.
Placentophagia (the behavior of ingesting the afterbirth after parturition) has been proposed to have physiological consequences that could facilitate a male’s responsiveness to offspring Non-genomic (epigenetic) transmission of paternal behavior from fathers to their sons has been reported to occur in laboratory studies of the biparental California mouse.
- Bateman's principle
- Behavioral ecology
- Challenge hypothesis
- Cinderella effect
- Cost of raising a child
- Darwinian medicine
- Evolutionary neuroscience
- Evolutionary psychology
- Field metabolic rate
- Human physiology
- Kin selection
- Life history theory
- Parental investment
- Peromyscus californicus
- r/K selection theory
- Social behavior
- Tinbergen's four questions
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