In
animalAnimals are a major group of mostly 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...
s,
infanticide involves the
killKILL is the sixth and most recent album by Detroit rock band Electric Six. It was released through Metropolis Records on October 20 2009....
ing of young
offspringIn biology, offspring is the product of reproduction, 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
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
, and is studied in
zoologyZoology, also spelled zoölogy, is the branch of biology that focuses on the structure, function, behavior, and evolution of animals. The zoologist's pronunciation of "zoology" is , though a common spelling pronunciation is .-Systems of classification:...
, specifically in the field of
ethologyEthology is the scientific study of animal behavior, and a sub-topic of zoology....
.
Ovicide is the analogous destruction of
eggIn most birds and reptiles, an egg is the zygote, resulting from fertilization of the ovum. To enable incubation the egg is usually kept within a favourable temperature range as it nourishes and protects the growing embryo. When the embryo is adequately developed it breaks out of the egg in the...
s. Although
human infanticideInfanticide is the practice of someone intentionally killing an infant. Often it is the mother who commits the act, but criminology recognizes various forms of non-maternal child murder. 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
rotiferThe 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,
insectInsects are arthropods, having a hard exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae. They are the most diverse group of animals on the planet and include more than a million species that are already described. Insects represent more than half of all...
s,
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
,
amphibianAmphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic animals that metamorphose from a juvenile water-breathing form, to an adult air-breathing form. Though amphibians typically have four limbs, the Caecilians are notable for being limbless. Unlike other land...
s,
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s and
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s. Infanticide can be practiced by both
maleMale refers to the 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
femaleFemale is the sex of an organism, or a part of an organism, which produces 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 conflictSexual conflict occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, leading to evolutionary arms race between males and females...
has the general theme of the killer (often male) becoming the new
sexualSexual reproduction is characterized by processes that pass a combination of genetic material to offspring, resulting in diversity. The main two processes are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the restoration...
partner of the victim's parent which would otherwise be unavailable to it. This represents a gain in
fitnessFitness is a central concept in evolutionary theory. It describes the capability of an individual of certain genotype to reproduce, and usually is equal to the proportion of the individual's genes in all the genes of the next generation...
by the killer, and a loss in fitness by the
parentA parent is a mother or father; one who sires or gives birth to and/or nurtures and raises an offspring. The different roles of parents vary throughout the tree of life, and are especially complex in human culture.- Father :...
s of the offspring killed. This is a type of
evolutionary struggleIn 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
sexIn 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 its own counter-adaptations which 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 often involves consumption of the young themselves, which is termed filial cannibalism. The behavior is widespread in fishes, and is seen in terrestrial animals as well.
HumanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
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
groupIn 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 evolutionThe gene-centered view of evolution, gene selection theory or selfish gene theory holds that natural selection acts through differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation...
), 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 principleIn biology, Bateman's principle is the theory that females almost always invest more energy into producing offspring than males, 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 monkeyThe 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, scrubland, and mountainous...
found in
IndiaIndia, 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, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal...
. They are a
socialIn biology, psychology 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 has not been observed in this species, however.
This behavior not only reduces
intraspecific competitionCompetition among individuals of the same species is referred to as intraspecific competition. Grasshoppers provide an animal example. By eating grass, individual grasshoppers deprive their fellow conspecifics of food...
between the incumbent's offspring and those of other males and increases the
parental investmentIn 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
milkMilk is an opaque white liquid produced by the mammary glands of mammals. It provides the primary source of nutrition for young mammals before they are able to digest other types of food. The early lactation milk is known as colostrum, and carries the mother's antibodies to the baby. It can reduce...
. 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 poolIn 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 selectionNatural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations...
).
Similar behavior is also seen in male
lionThe Lion is one of 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
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
s, and female lions only give birth once every two years, so the
selectiveIn the context of evolution, certain traits or alleles of a species 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 succeeding generation than...
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
miceMICE is an acronym for:*Muon Ionization Cooling Experiment*"Money, Ideology, Compromise, Ego", four factors by which spies may be recruited. See MICE .*"Meetings, Incentives, Conferencing, Exhibitions", terminology for banquets, etc., in a hotel....
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 rhythmA circadian rhythm is a roughly-24-hour cycle in the biochemical, physiological or behavioral processes of living entities, including plants, animals, fungi and cyanobacteria...
s (see
chronobiologyChronobiology is a field of science that examines periodic phenomena in living organisms and their adaptation to solar and lunar related rhythms. These cycles are known as biological rhythms. "Chrono" pertains to time and "biology" pertains to the study, or science, of life...
), 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.
GerbilA 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 jacanaThe 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 excusively the male sex which
broodsIncubation is the process by which birds 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 sitting on eggs to incubate...
, while females defend their territory. In this
experimentIn scientific research, an experiment is a method of investigating causal relationships among variables, or to test a hypothesis. An experiment is a cornerstone of the empirical approach to acquiring data about the world and is used in both natural sciences and social sciences...
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 bugBelostomatidae 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 and...
s.
Lethocerus deyrolleiLethocerus 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
vegetationVegetation 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
desiccatedDesiccation 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-well sealed container.-Science:-Desiccator:...
and will not hatch. In this species males are a scarce resource which females must sometimes compete for. Those that cannot find a free male will 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
evaporationEvaporation is the vaporization of a liquid and the reverse, of condensation. A type of phase transition, it is the process by which molecules in a liquid state spontaneously become gaseous . Generally, evaporation can be seen by the gradual disappearance of a liquid from a substance when exposed...
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 dogThe 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-polygynous
squirrelA squirrel is one of many small or medium-sized rodents in the family Sciuridae. In the English-speaking world, squirrel commonly refers to members of this family's genera Sciurus and Tamiasciurus, which are tree squirrels with large bushy tails, indigenous to Asia, the Americas and Europe....
s found mainly in the
United StatesThe 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 experimentA natural or Quasi-experiment is a naturally occurring instance of an observable phenomena which approximate or duplicate the properties of a controlled experiment. In contrast to laboratory experiments, these events aren't created by scientists, but yield data which nonetheless can be used to...
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 selectionSome organisms tend to exhibit strategies that favor the reproductive success of their relatives, even at a cost to their own survival and/or reproduction. The classic example is a eusocial insect colony, with sterile females acting as workers to assist their mother in the production of additional...
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
meerkatThe meerkat or suricate Suricata suricatta is a small mammal and a member of the mongoose family. It inhabits all parts of the Kalahari Desert in Botswana and South Africa. A group of meerkats is called a "mob", "gang" or "clan". A meerkat clan often contains about 20 meerkats at a time, but some...
(
Suricata suricatta), including cases of females killing their mother's and daughter's offspring. Infanticidal raids from neighboring groups also occurred.
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
energyIn physics, energy is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law...
and perhaps sustained serious
woundIn medicine, 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.-Types of wounds:-Open:Open wounds can be classified according to the...
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
infectionAn infection is the detrimental colonization of a host organism by a foreign species. In an infection, the infecting organism seeks to utilize the host's resources to multiply, usually at the expense of the host. The infecting organism, or pathogen, interferes with the normal functioning of the...
. It is also energetically
costlyCost-benefit analysis is a term that refers both to:* helping to appraise, or assess, the case for a project or proposal, which itself is a process known as project appraisal; and* an informal approach to making decisions of any kind....
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
NatureNature is a prominent British scientific journal, first published on 4 November 1869. Most scientific journals are now highly specialized, and Nature is among the few journals that still publish original research articles across a wide range of scientific...
is
acorn woodpeckerThe Acorn Woodpecker is a medium-sized woodpecker, 21 cm long with an average weight of 85 g.The adult has a black head, back, wings and tail, white forehead, throat, belly and rump. The eyes are white. The adult male has a red cap starting at the forehead, whereas females have a black area...
s. Females nest together, possibly because those nesting alone have their eggs constantly destroyed by rivals. Even so, eggs are consistently
removedEgg 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
incubateIncubation is the process by which birds 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 sitting on eggs to incubate...
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 which tend to prevent infanticide, and those which 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 effectThe Bruce effect is a form of pregnancy disruption in mammals in which exposure of a female to an unknown male results in pre- or postimplantation failure ....
. 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
smellingOlfaction refers to 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
urineUrine is a liquid waste product of the body secreted by the kidneys by a process of filtration from blood called urination and excreted through the urethra. Cellular metabolism generates numerous waste compounds, 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
motherA mother is a biological and/or social female parent of an offspring. Because of the complexity and differences of a mothers' social, cultural, and religious definitions and roles, it is challenging to define a mother to suit a universally accepted definition.-Biological mother:In the case of a...
. This is sometimes seen in
pigPigs are a genus of even-toed ungulates within the family Suidae. The name hog most commonly refers to the domestic pig in everyday parlance, but technically encompasses several distinct species, including the wild boar...
s, a behavior known as
savagingIn 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
giltGilt may refer to:*Gilding, the application of a thin layer of precious metal*Gilt-edged securities, also known as "gilts", government bonds issued in the United Kingdom for HM Treasury by the UK Debt Management Office...
s. Similar behavior has been observed in various animals such as
rabbitRabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. There are seven different genera in the family classified as rabbits, including the European rabbit , Cottontail rabbit , and the Amami rabbit...
s and
burying beetleBurying 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...
s.
Paternal
Paternal infanticide—where fathers eat their own offspring—may also occur. When young
bassBass 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." The collective name for a group...
hatch from the
spawnSpawning is the production or depositing of large quantities of eggs in water. The process is done by aquatic animals such as amphibians and fish.- Types of egg-layers :*egg scatterers*nest builders*egg hangers*mouth breeders*egg buriers...
, 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 beeHoney bees are a subset of bees, 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
workerEusociality 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
geneticsGenetics, , a discipline of biology, is the science of heredity and variation in living organisms. The fact that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding...
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
recessiveIn genetics, dominance describes a relationship between different forms of a gene at a particular physical location on a chromosome. Typical plants and animals have two sets of chromosomes, one set inherited from each parent, and are described as diploid. They therefore have two alleles at each...
, only being expressed when both
alleleAn allele is one of a series of different forms of a gene. The word is a short form of allelomorph , which was used in the early days of genetics to describe variant forms of a gene detected as different phenotypes...
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 UniversityCornell University is a private university located in Ithaca, New York, USA, that is a member of the Ivy League.Cornell counts more than 255,000 living alumni, 28 Rhodes Scholars and 41 Nobel laureates affiliated with the university as faculty or students...
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 abuseChild abuse is the physical and/or psychological/emotional mistreatment of children. In the United States, the Centers for Disease Control and Prevention define child maltreatment as any act or series of acts or commission or omission by a parent or other caregiver that results in harm, potential...
. 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
criminalCrime is the breach of one or more rules or laws for which some governing authority, via mechanisms such as police power, may ultimately prescribe a conviction...
. Nonetheless, it still takes place — in the
Western worldThe Western world, also known as the West and the Occident , is a term that can have multiple meanings depending on its context...
usually because of the parent's
mental illnessA mental disorder or mental illness is a psychological or behavioral pattern that occurs in an individual and is thought to cause distress or disability that is not expected as part of normal development or culture. The recognition and understanding of mental disorders has changed over time and...
or
violent behaviorViolence is the expression of physical or verbal force against self or other, compelling action against one's will on pain of being hurt. Variant uses of the term refer to the destruction of non-living objects . Worldwide, violence is used as a tool of manipulation and also is an area of concern...
, and in some
poor countriesThe term Third World arose during the Cold War to define countries that remained non-aligned or neutral with either capitalism and NATO or communism and the Soviet Union...
as a form of
population controlPopulation control is the practice of artificially altering the rate of population growth. Historically, 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 high or increasing...
, sometimes with tacit societal acceptance. Female infanticide, a form of sex-selective infanticide, is more common than the killing of male offspring.
See also
- Concealed ovulation
Human females have concealed ovulation or hidden estrus. Most female animals show distinctive signs when they are "in heat". These include swelling and redness of the genitalia in baboons and bonobos Pan paniscus, pheromone release in the feline family, etc. By comparison, human females have few...
(the evolution of which may be a counter-adaptation to infanticide by males)
- Parent-offspring conflict
Parent-offspring conflict is a term coined in 1974 by Robert Trivers. It is used to signify the evolutionary conflict arising from differences in optimal parental investment to an offspring from the standpoint of the parent and the offspring...
- Parricide
Parricide is defined as:#the act of murdering one's father , mother or other close relative, but usually not children ....
- Runt
A runt is a smaller specimen in a group of animals, usually of offspring in a litter.It may also refer to:*A breed of Dove related to the carrier pigeon*Runt , an album by Todd Rundgren*Runt: The Ballad of Todd Rundgren, an album by Todd Rundgren...
- Sexual cannibalism
Sexual cannibalism is a special case of cannibalism in which a female organism kills and consumes a male of the same species before, during, or after copulation. Rarely, these roles are reversed...
- Sexual selection
Sexual selection is the theory proposed by Charles Darwin that states that certain evolutionary traits can be explained by intraspecific competition. Darwin defined sexual selection as the effects of the "struggle between the individuals of one sex, generally the males, for the possession of the...
- Siblicide
Siblicide , the death of an individual by its close relatives may occur directly between siblings or indirectly across the parent-offspring relationship and is seen to have beneficial indirect results for the genetic viability of a population or direct results for the recipient individuals.Cattle...
- Sociobiology
Sociobiology is a synthesis of scientific disciplines which attempts to explain social behavior in animal species by considering the Darwinian advantages specific behaviors may have. It is often considered a branch of biology and sociology, but also draws from ethology, anthropology, evolution,...
Further reading
- Hausfater, G. & S. B. Hrdy (1984) Infanticide: Comparative and evolutionary perspectives New York, Aldine. 598 p. ISBN 0202020223
- Parmigiani, S. & F. S. vom Saal (1994) Infanticide and parental care London: Harwood. 493 p. ISBN 9783718655052
- C. P. van Schaik & C. H. Janson (2000) Infanticide by males and its implications Cambridge University Press. 569 p. ISBN 0521772958