Infanticide (zoology) - AbsoluteAstronomy.com

Animal

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s, infanticide involves the kill

KILL

KILL is the sixth album by Detroit rock band Electric Six.In initial press releases, the band described the album as being a return to a sound more akin to their debut album, but this was later revealed by front-man Dick Valentine to be more gimmick than truth.An explicit video was released for...

ing of young offspring

Offspring

In biology, offspring is the product of reproduction, of a new organism produced by one or more parents.Collective offspring may be known as a brood or progeny in a more general way...

by a mature animal of its own species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

, and is studied in zoology

Zoology

Zoology |zoölogy]]), is the branch of biology that relates to the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct...

, specifically in the field of ethology

Ethology

Ethology is the scientific study of animal behavior, and a sub-topic of zoology....

. Ovicide is the analogous destruction of egg

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

s. Although human infanticide

Infanticide

Infanticide or infant homicide is the killing of a human infant. Neonaticide, a killing within 24 hours of a baby's birth, is most commonly done by the mother.In many past societies, certain forms of infanticide were considered permissible...

has been widely studied, the practice has been observed in many other species throughout the animal kingdom. These include microscopic rotifer

Rotifer

The rotifers make up a phylum of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John Harris in 1696, and other forms were described by Anton van Leeuwenhoek in 1703...

s, insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, amphibian

Amphibian

Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

s, bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s and mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s. Infanticide can be practiced by both male

Male

Male refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...

s and female

Female

Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...

s.

Infanticide caused by sexual conflict

Sexual conflict

Sexual conflict occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly the mode and frequency of mating, leading to an evolutionary arms race between males and females. The conflict encompasses the actions and behaviors of both sexes to influence...

has the general theme of the killer (often male) becoming the new sexual

Sexual reproduction

Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...

partner of the victim's parent, which would otherwise be unavailable. This represents a gain in fitness

Fitness (biology)

Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...

by the killer, and a loss in fitness by the parent

Parent

A parent is a caretaker of the offspring in their own species. In humans, a parent is of a child . Children can have one or more parents, but they must have two biological parents. Biological parents consist of the male who sired the child and the female who gave birth to the child...

s of the offspring killed. This is a type of evolutionary struggle

Evolutionary arms race

In evolutionary biology, an evolutionary arms race is an evolutionary struggle between competing sets of co-evolving genes that develop adaptations and counter-adaptations against each other, resembling an arms race, which are also examples of positive feedback...

between the two sex

Sex

In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...

es, in which the victim sex may have counter-adaptations that reduce the success of this practice. It may also occur for other reasons, such as the struggle for food between females. In this case individuals may even kill closely related offspring.

Filial infanticide occurs when a parent kills its own offspring. This sometimes involves consumption of the young themselves, which is termed filial cannibalism

Filial cannibalism

Filial cannibalism occurs when an adult individual of a species consumes all or part of the young of its own species or immediate offspring. Filial cannibalism occurs in many animal species ranging from mammals to insects, and is especially prevalent in various species of fish...

. The behavior is widespread in fishes, and is seen in terrestrial animals as well. Human

Human

Humans are the only living species in the Homo genus...

infanticide has been recorded in almost every culture. A unique aspect of human infanticide is selective killing based on gender.

Background

Infanticide only came to be seen as a significant occurrence in nature quite recently. At the time it was first seriously treated by Yukimaru Sugiyama, infanticide was attributed to stress causing factors like overcrowding and captivity, and was considered pathological and maladaptive. Classical ethology held that conspecifics (members of the same species) rarely killed each other. By the 1980s it had gained much greater acceptance. Possible reasons it was not treated as a serious natural phenomenon include its abhorrence to people, the popular group

Group selection

In evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness of individuals within that group....

and species selectionist notions of the time (the idea that individuals behave for the good of the group or species; compare with gene-centered view of evolution

Gene-centered view of evolution

The gene-centered view of evolution, gene selection theory or selfish gene theory holds that evolution occurs through the differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation, with gene defined as...

), and the fact that it is very difficult to observe in the field.

Infanticide involving sexual conflict

This form of infanticide represents a struggle between the sexes, where one sex exploits the other, much to the latter's disadvantage. It is usually the male who benefits from this behavior, though in cases where males play similar roles to females in parental care the victim and perpetrator may be reversed (see Bateman's principle

Bateman's principle

In biology, Bateman's principle is the theory that females almost always invest more energy into producing offspring than males invest, and therefore in most species females are a limiting resource over which the other sex will compete...

for discussion of this asymmetry).

By males

Hanuman langurs (or gray langurs) are an Old World monkey

Old World monkey

The Old World monkeys or Cercopithecidae are a group of primates, falling in the superfamily Cercopithecoidea in the clade Catarrhini. The Old World monkeys are native to Africa and Asia today, inhabiting a range of environments from tropical rain forest to savanna, shrubland and mountainous...

found in India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

. They are a social

Social behavior

In physics, physiology and sociology, social behavior is behavior directed towards society, or taking place between, members of the same species. Behavior such as predation which involves members of different species is not social...

animal, living in groups. Each group is generally dominated by a single male, with many females, though the male must struggle for control of the group with other males. When a male tries to take over a group, there is a violent struggle with the existing male. If successful in overthrowing the previous male, infants of the females are then killed. This infanticidal period is limited to the window just after the group is taken over. Cannibalism, however, has not been observed in this species.

This behavior not only reduces intraspecific competition

Intraspecific competition

Intraspecific competition is a particular form of competition in which members of the same species vie for the same resource in an ecosystem...

between the incumbent's offspring and those of other males and increases the parental investment

Parental investment

In evolutionary biology, parental investment is any parental expenditure that benefits one offspring at a cost to parents' ability to invest in other components of fitness...

afforded to their own young, but also allows females to become sexually receptive sooner. This is because females of this species, as well as many other mammals, do not ovulate during the period in which they produce milk. It then becomes easier to see how this behavior could have evolved. If a male kills a female's young, they stop lactating and are able to become pregnant again. As males are in a constant struggle to protect their group, those that express infanticidal behavior will contribute a larger portion to future gene pool

Gene pool

In population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...

s (see natural selection

Natural selection

Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

).

Similar behavior is also seen in male lion

Lion

The lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg in weight, it is the second-largest living cat after the tiger...

s, among other species, who also kill young cubs, allowing them to impregnate the females. Unlike langurs, male lions live in small groups, which cooperate to take control of a pride from an existing group. They will attempt to kill any cubs that are roughly 9 months old or less, though as in other species, the female will attempt to defend their cubs viciously. Males have, on average, only a two year window in which to pass on their gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s, and female lions only give birth once every two years, so the selective

Selection

In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...

pressure from them to behave like this is strong. In fact it is estimated that a quarter of cubs dying in the first year of their life are victims of infanticide.

Male mice

MICE

-Fiction:*Mice , alien species in The Hitchhiker's Guide to the Galaxy*The Mice -Acronyms:* "Meetings, Incentives, Conferencing, Exhibitions", facilities terminology for events...

show great variation in behavior over time. After fertilizing a female, they become aggressive towards mouse pups for three weeks, killing any they come across. After this period however, their behavior changes dramatically, and they become paternal, caring for their own offspring. This lasts for almost two months, but afterwards they become infanticidal once more. It is no coincidence here that the female gestation period is three weeks as well, or that it takes roughly two months for pups to become fully weaned and leave their nest. The proximate mechanism that allows for the correct timing of these periods involves circadian rhythm

Circadian rhythm

A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...

s (see chronobiology

Chronobiology

Chronobiology is a field of biology that examines periodic phenomena in living organisms and their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος , and biology, which pertains to the study, or science,...

), each day and night cycle affecting the mouse's internal neural physiology, and disturbances in the duration of these cycles results in different periods of time between behaviors. The adaptive value of this behavior switching is twofold; infanticide removes competitors for when the mouse does have offspring, and allows the female victims to be impregnated earlier than if they continued to care for their young, as mentioned above.

Gerbil

Gerbil

A gerbil is a small mammal of the order Rodentia. Once known simply as "desert rats", the gerbil subfamily includes about 110 species of African, Indian, and Asian rodents, including sand rats and jirds, all of which are adapted to arid habitats...

s, on the other hand, no longer commit infanticide once they have paired with a female, but actively kill and eat other offspring when young. The females of this species behave much like male mice, hunting down other litters except when rearing their own.

Prospective infanticide

Prospective infanticide is a subset of sexual competition infanticide in which young born after the arrival of the new male are killed. This is less common than infanticide of existing young, but can still increase fitness in cases where the offspring could not possibly have been fathered by the new mate, i.e. one gestation or fertility period. This is known to occur in lions and langurs, and has also been observed in other species such as house wrens. In birds, however, the situation is more complex, as female eggs are fertilized one at a time, with a 24-hour delay between each. Males may destroy clutches laid 12 days or more after their arrival, though their investment of around 60 days of parental care is large, so a high level of parental certainty is needed.

By females

Females are also known to display infanticidal behavior. This may appear unexpected, as the conditions described above do not apply. Males are not always an unlimited resource though - in some species, males provide parental care to their offspring, and females may compete indirectly with others by killing their offspring, freeing up the limiting resource that the males represent. This has been documented in research by Stephen Emlen and Natalie Demong on wattled jacana

Wattled Jacana

The Wattled Jacana Jacana jacana is a wader which is a resident breeder from western Panama and Trinidad south through most of South America east of the Andes....

s (Jacana jacana), a tropical wading bird. With the wattled jacana, it is exclusively the male sex that broods

Avian incubation

Incubation refers to the process by which certain oviparous animals hatch their eggs, and to the development of the embryo within the egg. The most vital factor of incubation is the constant temperature required for its development over a specific period. Especially in domestic fowl, the act of...

, while females defend their territory. In this experiment

Experiment

An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...

Demong and Emlen found that removing females from a territory resulted in nearby females attacking the chicks of the male in most cases, evicting them from their nest. The males then fertilized the offending females and cared for their young. Emlen describes how he "shot a female one night, and [...] by first light a new female was already on the turf. I saw terrible things—pecking and picking up and throwing down chicks until they were dead. Within hours she was soliciting the male, and he was mounting her the same day. The next night I shot the other female, then came out the next morning and saw the whole thing again."

Infanticide is also seen in giant water bug

Giant water bug

Belostomatidae is a family of insects in the order Hemiptera, known as giant water bugs or colloquially as toe-biters, electric-light bugs and Alligator Ticks . They are the largest insects in the order Hemiptera, and occur worldwide, with most of the species in North America, South America,...

s. Lethocerus deyrollei
Lethocerus deyrollei
Lethocerus deyrollei is a species of giant water bug in the genus Lethocerus. They are large , predatory and nocturnal insects. They live in still waters with vegetation, hatching in the summer months and then overwintering half a year later as adults.The eggs of this species are laid out of...

is a large and nocturnal predatory insect found in still waters near vegetation

Vegetation

Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...

. In this species the males take care of masses of eggs by keeping them hydrated with water from their bodies. Without a male caring for the eggs like this, they become desiccated

Desiccation

Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...

and will not hatch. In this species, males are a scarce resource that females must sometimes compete for. Those that cannot find a free male often stab the eggs of a brooding one. As in the above case, males then fertilize this female and care for her eggs. Noritaka Ichikawa has found that males only moisten their eggs during the first 90 seconds or so, after which all of the moisture on their bodies has evaporated. However, they guard the egg masses for as long as several hours at a time, when they could be hunting prey. They do not seem to prevent further evaporation

Evaporation

Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....

by staying guard, as males that only guarded the nest for short periods were seen to have similar hatching rates in a controlled experiment where there were no females present. It seems rather that males are more successful in avoiding infanticidal females when they are out of the water with their eggs, which might well explain the ultimate cause of this behavior.

Resource competition

Black-tailed prairie dog

Black-tailed Prairie Dog

The black-tailed prairie dog , is a rodent of the family Sciuridae found in the Great Plains of North America from about the USA-Canada border to the USA-Mexico border. Unlike some other prairie dogs, these animals do not truly hibernate. The black-tailed prairie dog can be seen aboveground in...

s are colonially-living, harem

Harem

Harem refers to the sphere of women in what is usually a polygynous household and their enclosed quarters which are forbidden to men...

-polygynous squirrel

Squirrel

Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...

s found mainly in the United States

Fauna of the United States

The Fauna of the United States covers a wide variety of species.-Discussions by state:* Fauna of Alabama* Fauna of Alaska* Fauna of Arizona* Fauna of Arkansas* Fauna of California* Fauna of Colorado* Fauna of Connecticut* Fauna of Delaware...

. Their living arrangement involves one male living with four or so females in a territory defended by all individuals, and underground nesting. Black-tails only have one litter per year, and are in estrous for only a single day around the beginning of spring.

A seven-year natural experiment

Natural experiment

A natural experiment is an observational study in which the assignment of treatments to subjects has been haphazard: That is, the assignment of treatments has been made "by nature", but not by experimenters. Thus, a natural experiment is not a controlled experiment...

by John Hoogland and others from the University of Princeton revealed that infanticide is widespread in this species, including infanticide from invading males and immigrant females, as well as occasional cannibalism of an individual's own offspring. The surprising finding of the study was that by far the most common type of infanticide involved the killing of close kin's offspring. This seems illogical, as kin selection

Kin selection

Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...

favors behaviors that promote the well-being of closely related individuals. It was postulated that this form of infanticide is more successful than trying to kill young in nearby groups, as the whole group must be bypassed in this case, while within a group only the mother need be evaded. Marauding behavior is evidently adaptive, as infanticidal females had more and healthier young than others, and were heavier themselves as well. This behavior appears to reduce competition with other females for food, and future competition among offspring.

Similar behavior has been reported in the meerkat

Meerkat

The meerkat or suricate, Suricata suricatta, is a small mammal belonging to the mongoose family. Meerkats live in all parts of the Kalahari Desert in Botswana, in much of the Namib Desert in Namibia and southwestern Angola, and in South Africa. A group of meerkats is called a "mob", "gang" or "clan"...

(Suricata suricatta), including cases of females killing their mother's, sister's, and daughter's offspring. Infanticidal raids from neighboring groups also occurred.

Other

Bottlenose dolphin

Bottlenose Dolphin

Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...

s have been reported to kill their young through impact injuries. Dominant male langurs tend to kill the existing young upon taking control of a harem. There has been sightings of infanticide in the leopard

Leopard

The leopard , Panthera pardus, is a member of the Felidae family and the smallest of the four "big cats" in the genus Panthera, the other three being the tiger, lion, and jaguar. The leopard was once distributed across eastern and southern Asia and Africa, from Siberia to South Africa, but its...

population.

Costs of the behavior

While it may be beneficial for some species to behave this way, infanticide is not without risks to the perpetrator. Having already exhausted energy

Energy

In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

and perhaps sustained serious wound

Wound

A wound is a type of injury in which skin is torn, cut or punctured , or where blunt force trauma causes a contusion . In pathology, it specifically refers to a sharp injury which damages the dermis of the skin.-Open:...

s in a fight with another male, attacks from females who vigorously defend their offspring may be telling for harem-polygynous males, with a risk of infection

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

. It is also energetically costly

Cost-benefit analysis

Cost–benefit analysis , sometimes called benefit–cost analysis , is a systematic process for calculating and comparing benefits and costs of a project for two purposes: to determine if it is a sound investment , to see how it compares with alternate projects...

to pursue a mother's young, which may try to escape.

Costs of the behavior described in prairie dogs include the risk to an individual of losing their own young while killing another's, not to mention the fact that they are killing their own relatives. In a species where infanticide is common, perpetrators may well be victims themselves in the future, such that they come out no better off; but as long as an infanticidal individual gains in reproductive output by its behavior, it will tend to become common. Further costs of the behavior in general may be induced by counter-strategies evolved in the other sex, as described below.

As a cost of social behavior

Taking a broader view of the black-tailed prairie dog situation, infanticide can be seen as a cost of social living. If each female were to have her own private nest away from others, she would be much less likely to have her infants killed when absent. This, and other costs such as increased spread of parasites, must be made up for by other benefits, such as group territory defense and increased awareness of predators.

An avian example published in Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

is acorn woodpecker

Acorn Woodpecker

The Acorn woodpecker is a medium-sized woodpecker, 21 cm long with an average weight of 85 g.-Description:...

s. Females nest together, possibly because those nesting alone have their eggs constantly destroyed by rivals. Even so, eggs are consistently removed

Egg tossing (behavior)

Egg tossing is a behavior observed in some species of birds and is related to infanticide. The activity is performed so as to increase the chances that newly laid eggs which are genetically closer to the female receive a better chance of survival...

at first by nest partners themselves, until the entire group lays on the same day. They then cooperate and incubate

Avian incubation

the eggs as a group, but by this time a significant proportion of their eggs have been lost because of this ovicidal behavior.

Counter-strategies

Because this form of infanticide reduces the fitness of killed individuals' parents, animals have evolved a range of counter-strategies against this behavior. These may be divided into two very different classes - those that tend to prevent infanticide, and those that minimize losses.

Loss minimization

Some females abort or resorb their own young while they are still in development after a new male takes over; this is known as the Bruce effect

Bruce effect

The Bruce effect, or pregnancy block, refers to the tendency for female rodents to terminate their pregnancies following exposure to the scent of an unfamiliar male. The effect has primarily been studied in laboratory mice , but is also observed in deer-mice, meadow voles, and collared lemmings...

. This may prevent their young from being killed after birth, saving the mother wasted time and energy. However, this strategy also benefits the new male. In mice this can occur by the proximate mechanism of the female smelling

Olfaction

Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...

the odor of the new male's urine

Urine

Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...

Preventative adaptations

Infanticide in burying beetles may have led to male parental care. In this species males often cooperate with the female in preparing a piece of carrion, which is buried with the eggs and eaten by the larvae when they hatch. Males may also guard the site alongside the female. It is apparent from experiments that this behavior does not provide their young with any better nourishment, nor is it of any use in defending against predators. However, other burying bugs may try to take their nesting space. When this occurs, a male-female pair is over twice as successful in nest defense, preventing the ovicide of their offspring.

Female langurs may leave the group with their young alongside the outgoing male, and others may develop a false estrous and allow the male to copulate, deceiving him into thinking she is actually sexually receptive. Females may also have sexual liaisons with other males. This promiscuous behavior is adaptive, because males will not know whether it is their own offspring they are killing or not, and may be more reluctant or invest less effort in infanticide attempts. Lionesses cooperatively guard against scouting males, and a pair were seen to violently attack a male after it killed one of their young. Resistance to infanticide is also costly, though: for instance, a female may sustain serious injuries in defending her young. At times it is simply more advantageous to submit than to fight.

Infanticide by parents and caregivers

Filial infanticide occurs when a parent kills its own offspring. Both male and female parents have been observed to do this, as well as sterile worker castes in some eusocial animals.

Maternal

Maternal infanticide occurs when newborn offspring are killed by their mother

Mother

A mother, mum, mom, momma, or mama is a woman who has raised a child, given birth to a child, and/or supplied the ovum that grew into a child. Because of the complexity and differences of a mother's social, cultural, and religious definitions and roles, it is challenging to specify a universally...

. This is sometimes seen in pig

Pig

A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...

s, a behavior known as savaging

Savaging

In animal science, savaging is overt aggression, usually including cannibalistic infanticide of newborn offspring, by a mother animal. It is particularly prevalent among pigs, where it affects up to 5% of gilts....

, which affects up to 5% of gilts. Similar behavior has been observed in various animals such as rabbit

Rabbit

Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...

s and burying beetle

Burying beetle

Burying beetles or sexton beetles are the best-known members of the family Silphidae . Burying beetles are true to their name. Most of these beetles are black with red markings on the elytra . They bury the carcasses of small vertebrates such as birds and rodents as a food source for their larvae...

Paternal

Paternal infanticide—where fathers eat their own offspring—may also occur. When young bass

Bass (fish)

Bass is a name shared by many different species of popular gamefish. The term encompasses both freshwater and marine species. All belong to the large order Perciformes, or perch-like fishes, and in fact the word bass comes from Middle English bars, meaning "perch."-Types of basses:*The temperate...

hatch from the spawn

Spawn (biology)

Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...

, the father guards the area, circling around them and keeping them together, as well as providing protection from would-be predators. After a few days, most of the fish will swim away. At this point the male's behavior changes: instead of defending the stragglers, he treats them as any other small prey, and eats them.

Worker caste killing young

Honey bee

Honey bees are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis...

s may become infected with a bacterial disease called foul brood, which attacks the developing bee larva while still living in the cell. Some hives however have evolved a behavioral adaptation that resists this disease: the worker

Eusociality

Eusociality is a term used for the highest level of social organization in a hierarchical classification....

bees selectively kill the infected individuals by removing them from their cells and tossing them out of the hive, preventing it from spreading. The genetics

Genetics

Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

of this behavior are quite complex. Experiments by Rothenbuhler showed that the 'hygienic' behavior of the queen was lost by crossing with a non-hygienic drone. This means that the trait must be recessive

Dominance relationship

Dominance in genetics is a relationship between two variant forms of a single gene, in which one allele masks the effect of the other in influencing some trait. In the simplest case, if a gene exists in two allelic forms , three combinations of alleles are possible: AA, AB, and BB...

, only being expressed when both allele

Allele

An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...

s contain the gene for hygienic behavior. Furthermore, the behavior is dependent on two separate loci. A backcross produced a mixed result. The hives of some offspring were hygienic, while others were not. There was also a third type of hive where workers removed the wax cap of the infected cells, but did nothing more. What was not apparent was the presence of a fourth group who threw diseased larvae out of the hive, but did not have the uncapping gene. This was suspected by Rothenbuhler however, who manually removed the caps, and found some hives proceeded to clear out infected cells.

Perceptions and importance

Like many of the darker aspects of nature, infanticide is a subject that many find discomforting. Cornell University

Cornell University

Cornell University is an Ivy League university located in Ithaca, New York, United States. It is a private land-grant university, receiving annual funding from the State of New York for certain educational missions...

ethologist Glenn Hausfater states that "infanticide has not received much study because it's a repulsive subject [...] Many people regard it as reprehensible to even think about it."

Research into infanticide in animals is in part motivated by the desire to understand human behaviors, such as child abuse

Child abuse

Child abuse is the physical, sexual, emotional mistreatment, or neglect of a child. In the United States, the Centers for Disease Control and Prevention and the Department of Children And Families define child maltreatment as any act or series of acts of commission or omission by a parent or...

. Hausfater explains that researchers are "trying to see if there's any connection between animal infanticide and child abuse, neglect and killing by humans [...] We just don't know yet what the connections are."

Infanticide by humans

Infanticide has been, and still is, practiced by some cultures, groups, or individuals. It is often, but not always, the mother who commits the act. In many past societies, certain forms of infanticide were considered permissible, whereas in most modern societies the practice is considered immoral and criminal

Crime

Crime is the breach of rules or laws for which some governing authority can ultimately prescribe a conviction...

. Nonetheless, it still takes place — in the Western world

Western world

The Western world, also known as the West and the Occident , is a term referring to the countries of Western Europe , the countries of the Americas, as well all countries of Northern and Central Europe, Australia and New Zealand...

usually because of the parent's mental illness

Mental illness

A mental disorder or mental illness is a psychological or behavioral pattern generally associated with subjective distress or disability that occurs in an individual, and which is not a part of normal development or culture. Such a disorder may consist of a combination of affective, behavioural,...

or violent behavior

Violence

Violence is the use of physical force to apply a state to others contrary to their wishes. violence, while often a stand-alone issue, is often the culmination of other kinds of conflict, e.g...

, and in some poor countries

Third World

The term Third World arose during the Cold War to define countries that remained non-aligned with either capitalism and NATO , or communism and the Soviet Union...

as a form of population control

Population control

Human population control is the practice of artificially altering the rate of growth of a human population.Historically, human population control has been implemented by limiting the population's birth rate, usually by government mandate, and has been undertaken as a response to factors including...

, sometimes with tacit societal acceptance. Female infanticide, a form of sex-selective infanticide, is more common than the killing of male offspring.