Parental care is a behavioural and evolutionary strategy adopted by some animals, making a parental investment into the evolutionary fitness of their offspring. This strategy involves devoting more effort to a relatively small number of offspring in order to improve offspring reproductive success and the overall fitness of the species; an opposite strategy is to produce a relatively large number of small offspring, often as eggs, and to invest little to no effort into rearing the young.
Although parental care increases the evolutionary fitness of the offspring receiving the care, parental care produces a cost for the parent organism. Energy expended on caring for the offspring and lost mating opportunities are the main costs experienced. Due to the associated costs, parental care will only evolve in a species from a previous condition of no parental care when the costs to the parent associated with providing the care are outweighed by the benefits to the offspring receiving the care.
Parental care is seen in many insects, notably the social insects such as ants, bees and wasps; in certain fishes, such as the mouthbrooders; widely in birds; and especially widely in mammals, which share two major adaptations for care of the young, namely gestation (development of the embryo inside the mother's body) and production of milk.
Some insects, but especially the Hymenoptera (ants, bees and wasps), invest substantial effort in caring for their young. The type and amount of care varies widely. Solitary wasps such as the potter wasps (Eumeninae) build nests for their young, provisioning them with food, often caterpillars, caught by the mother. The nests are then sealed, and the young live on the food until they leave the nest as adults. In contrast, social wasps and honeybees raise young in substantial colonies, with eggs laid mainly by queens (mothers), and the young cared for mainly by workers (sisters of the young).
Outside the Hymenoptera, parental care is found among the burying beetles and the magnificent salt beetle. Subdued forms of parental care are also seen in the Lepidoptera, as in butterflies that lay eggs where the offspring will be able to feed. Crickets have also been known to lay eggs in optimal environments for the young.
Several different groups of fish have evolved parental care. The young may be guarded by either parent. Some fish such as pipefish, sea dragons and seahorses (Syngnathidae) have a form of male pregnancy, the female taking no part in caring for the young once she has laid her eggs. Males in other species may take a role in guarding the eggs before they hatch.
Mouthbrooding is the care given by some groups of fish (and a few other animals such as Darwin's frog) to their offspring by holding them in their mouth for extended periods of time. Mouthbrooding has evolved independently in several different families of fish including the cardinalfish, sea catfish, bagrid catfish, cichlids, snakeheads, jawfishes, gouramis, and arowanas.
Birds are distinctive in the way they care for their young. In over 90% of birds, both parents help to care for the young. This pattern may have originated in the stem reptiles (archosaurs) that gave rise to the birds, before they developed flight. Most birds, including passerines (perching birds), have their young born blind, naked and helpless (altricial), totally dependent for their survival on parental care. The young are typically raised in a nest; the parents catch food and regurgitate it for the young. Some birds such as pigeons create a "crop milk" which they similarly regurgitate. David Lack developed a hypothesis that clutch size has evolved in response to the costs of parental care known as Lack's principle. It has since seen modifications but is still used as a general model.
All the higher mammals (excluding the monotremes, namely the echidna and the platypus) share two major adaptations for care of their young, namely gestation (development of the embryo inside the mother's body, followed by live birth) and production of milk. Many mammals exhibit further parental care, including building a nest, digging a burrow, or feeding and guarding their young, often for a prolonged period.
Parenting or child rearing in humans is the process of promoting and supporting the physical, emotional, social, financial, and intellectual development of a child from infancy to adulthood. This goes far beyond anything found in other animals, including not only the provision of food, shelter, and protection from threats such as predators, but a prolonged period of support during which the child learns whatever is needed to live successfully in human society.
Parental care after the laying of eggs has been observed in 5% of caecilian species, 18% of salamander species and 6% of frog species, though this number is likely an underestimate due to taxonomic bias in research  and the cryptic nature of many species. Six modes of parental care are recognized among the Amphibia, in different species: egg attendance, egg transport, tadpole attendance, tadpole transport, tadpole feeding, and internal gestation in the oviduct (viviparity and ovoviviparity). Many species also care for offspring (either eggs or tadpoles) in specially adapted structures of their body. For example, the male pouched frog of eastern Australia protects tadpoles in pouches on the lateral surface of their skin, the gastric-brooding frog raised tadpoles (and potentially eggs) in their stomach and the common Suriname toad raises eggs embedded in the skin on its back.
In evolutionary biology, parental investment is the expenditure of time and effort towards rearing offspring that benefits the offspring's evolutionary fitness at a cost to parents' ability to invest in other components of the species' fitness. Parental care comprises a part of one kind of reproductive strategy in which parents choose to give each of a relatively small number of offspring an increased chance of surviving to reproduce themselves, and may accordingly be accompanied by the production of a small number of zygotes at a time, possibly only one.
The evolution of male parental care is particularly rare in non-monogamous species because predominantly, investing effort into mating is more evolutionarily-effective for males than providing parental care. One hypothesis regarding the evolution of male parental care in non-monogamous species suggests that parental behavior is correlated with increased siring of offspring. For instance, in mountain gorillas (Gorilla beringei), males of the upper tertile, regarding their frequency of interaction with young gorillas, regardless of the young’s parentage, fathered five times more offspring than males of the lower-two affiliative tertiles. Further, male burying beetles (Nicrophorus vespilloides) attracted three times more females when given the opportunity to breed and provide parental care compared to males that were not presented with a breeding opportunity. Species such as Gorilla beringei and Nicrophorus vespilloides indicate that selection may promote male parental care in non-monogamous species.