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Bisexual Species: Unorthodox Sex in the Animal Kingdom
Homosexual behavior is common in nature, and it plays an important role in survival
By Emily V. Driscoll
Two penguins native to Antarctica met one spring day in 1998 in a
tank at the Central Park Zoo in midtown Manhattan. They perched atop
stones and took turns diving in and out of the clear water below. They
entwined necks, called to each other and mated. They then built a nest
together to prepare for an egg. But no egg was forthcoming: Roy and
Silo were both male.
Robert Gramzay, a keeper at the zoo, watched the chinstrap penguin
pair roll a rock into their nest and sit on it, according to newspaper
reports. Gramzay found an egg from another pair of penguins that was
having difficulty hatching it and slipped it into Roy and Silo’s nest.
Roy and Silo took turns warming the egg with their blubbery
underbellies until, after 34 days, a female chick pecked her way into
the world. Roy and Silo kept the gray, fuzzy chick warm and
regurgitated food into her tiny black beak.
Like most animal species, penguins tend to pair with the opposite
sex, for the obvious reason. But researchers are finding that same-sex
couplings are surprisingly widespread in the animal kingdom. Roy and
Silo belong to one of as many as 1,500 species of wild and captive
animals that have been observed engaging in homosexual activity.
Researchers have seen such same-sex goings-on in both male and female,
old and young, and social and solitary creatures and on branches of the
evolutionary tree ranging from insects to mammals.
Unlike most humans, however, individual animals generally cannot be
classified as gay or straight: an animal that engages in a same-sex
flirtation or partnership does not necessarily shun heterosexual
encounters. Rather many species seem to have ingrained homosexual
tendencies that are a regular part of their society. That is, there are
probably no strictly gay critters, just bisexual ones. “Animals don’t
do sexual identity. They just do sex,†says sociologist Eric Anderson
of the University of Bath in England.
Nevertheless, the study of homosexual activity in diverse species
may elucidate the evolutionary origins of such behavior. Researchers
are now revealing, for example, that animals may engage in same-sex
couplings to diffuse social tensions, to better protect their young or
to maintain fecundity when opposite-sex partners are unavailable—or
simply because it is fun. These observations suggest to some that
bisexuality is a natural state among animals, perhaps Homo sapiens
included, despite the sexual-orientation boundaries most people take
for granted. “[In humans] the categories of gay and straight are
socially constructed,†Anderson says.
What is more, homosexuality among some species, including penguins,
appears to be far more common in captivity than in the wild. Captivity,
scientists say, may bring out gay behaviors in part because of a
scarcity of opposite-sex mates. In addition, an enclosed environment
boosts an animal’s stress levels, leading to a greater urge to relieve
the stress. Some of the same influences may encourage what some
researchers call “situational homosexuality†in humans in same-sex
settings such as prisons or sports teams.
Making Peace
Modern studies of animal homosexuality date to the late 19th century
with observations on insects and small animals. In 1896, for example,
French entomologist Henri Gadeau de Kerville of the Society of Friends
of Natural Sciences and the Museum of Rouen published a drawing of two
male scarab beetles copulating. Then, during the first half of the
1900s, various investigators described homosexual behavior in baboons,
garter snakes and gentoo penguins, among other species. Back then,
scientists generally considered homosexual acts among animals to be
abnormal. In some cases, they “treated†the animals by, say, castrating
them or giving them lobotomies.
At least one early report, however, was more than descriptive,
yielding insight into the possible origins of the behavior. In a 1914
lab experiment Gilbert Van Tassel Hamilton, a psychopathologist
practicing in Montecito, Calif., reported that same-sex behavior in 20
Japanese macaques and two baboons occurred largely as a way of making
peace with would-be foes. In the Journal of Animal Behavior Hamilton
observed that females offered sex to the more dominant macaques of the
same sex: “homosexual behavior is of relatively frequent occurrence in
the female when she is threatened by another female, but it is rarely
manifested in response to sexual hunger.†And in males, he penned,
“homosexual alliances between mature and immature males may possess a
defensive value for immature males, since they insure the assistance of
an adult defender in the event of an attack.â€
More recently,
some researchers studying bonobos (close relatives of the chimpanzee)
have come to similar conclusions. Bonobos are highly promiscuous, and
about half their sexual activity involves same-sex partners. Female
bonobos rub one another’s genitals so often that some scientists have
suggested that their genitalia evolved to facilitate this activity. The
female bonobo’s clitoris is “frontally placed, perhaps because
selection favored a position maximizing stimulation during the
genital-genital rubbing common among females,†wrote behavioral
ecologist Marlene Zuk of the University of California, Riverside, in
her 2002 book Sexual Selections: What We Can and Can’t Learn about Sex
from Animals. Male bonobos have been observed to mount, fondle and even
perform oral sex on one another.
Such behavior seems to ease social tensions. In Bonobo: The
Forgotten Ape (University of California Press, 1997), Emory University
primatologist Frans B. M. de Waal and his co-author photographer Frans
Lanting wrote that “when one female has hit a juvenile and the
juvenile’s mother has come to its defense, the problem may be resolved
by intense GG-rubbing between the two adults.†De Waal has observed
hundreds of such incidents, suggesting that these homosexual acts may
be a general peacekeeping strategy. “The more homosexuality, the more
peaceful the species,†asserts Petter Böckman, an academic adviser at
the University of Oslo’s Museum of Natural History in Norway. “Bonobos
are peaceful.â€
In fact, such acts are so essential to bonobo socialization that
they constitute a rite of passage for young females into adulthood.
Bonobos live together in groups of about 60 in a matriarchal system.
Females leave the group during adolescence and gain admission to
another bonobo clan through grooming and sexual encounters with other
females. These behaviors promote bonding and give the new recruits
benefits such as protection and access to food.
Defended Nest
In some birds, same-sex unions, particularly between males, might have
evolved as a parenting strategy to increase the survival of their
young. “In black swans, if two males find each other and make a nest,
they’ll be very successful at nest making because they are bigger and
stronger than a male and female,†Böckman says. In such cases, he says,
“having a same-sex partner will actually pay off as a sensible life
strategy.â€
In other instances, homosexual bonding between female parents can
boost the survival of offspring when male-female pairings are not
possible. In birds called oystercatchers, intense competition for male
mates would leave some females single were it not for polygamous trios.
In a study published in 1998 in Nature, zoologist Dik Heg and
geneticist Rob van Treuren, both then at the University of Groningen in
the Netherlands, observed that roughly 2 percent of oystercatcher
breeding groups consist of two females and a male. In some of these
families, Heg and van Treuren found, the females tend separate nests
and fight over the male, but in others, all three birds watch over a
single nest. In the latter case, the females bond by mounting each
other as well as the male. The cooperative triangles produce more
offspring than the competitive ones, because such nests are better
tended and protected from predators.
Such arrangements point to the evolutionary fitness of stable social
relationships, whatever their type. Biologist Joan E. Roughgarden of
Stanford University believes that evolutionary biologists tend to
adhere too strongly to Darwin’s theory of sexual selection and have
thus largely overlooked the importance of bonding and friendship to
animal societies and the survival of their young.“ [Darwin] equated
reproduction with finding a mate rather than paying attention to how
the offspring are naturally reared,†Roughgarden says.
Protection
of progeny, social bonding and conflict avoidance may not be the only
reasons animals naturally come to same-sex relationships. Many animals
do it simply “because they want to,†Böckman says. “People view animals
as robots who behave as their genes say, but animals have feelings, and
they react to those feelings.†He adds that “as long as they feel the
urge [for sex], they’ll go for it.â€
A recent finding indicates that homosexual behavior may be so common
because it is rooted in an animal’s brain wiring—at least in the case
of fruit flies. In a study appearing earlier this year in Nature
Neuroscience, neuroscientist David E. Featherstone of the University of
Illinois at Chicago and his colleagues found that they could switch on
homosexual leanings in fruit flies by manipulating a gene for a protein
they call “genderblind,†which regulates communication between neurons
that secrete and respond to the neurotransmitter glutamate.
Males that carried the mutant genderblind gene—which depressed
levels of the protein by about two thirds—were uncharacteristically
attracted to the chemical cues exuded by other males. As a result,
these mutant males courted and attempted to copulate with other males.
The finding suggests that wild fruit flies may be prewired for both
heterosexual and homosexual behavior, the authors write, but that the
genderblind protein suppresses the glutamate-based circuits that
promote homosexual behavior. Such brain architecture may enable
same-sex behavior to surface easily, supporting the notion that it
might confer an evolutionary advantage in some circumstances.
The Captivity Effect
In some less social species, homosexual behavior is almost unheard of
in wild animals but may surface in captivity. Wild koalas, which are
mostly solitary, seem to be strictly heterosexual. But in a 2007 study
veterinary scientist Clive J. C. Phillips of the University of
Queensland in Brisbane, Australia, and his colleagues observed 43
instances of homosexual activity among female koalas living in a
same-sex enclosure at the Lone Pine Koala Sanctuary. The captive
females shrieked male mating calls and mated with one another,
sometimes participating in multiple encounters of up to five koalas.
“The behavior in captivity was certainly enhanced in terms of
homosexual activity,†Phillips says.
He believes that the females acted this way in part because of
stress. Animals often experience stress in enclosed habitats and may
engage in homosexual behavior to relieve that tension. A lack of male
partners probably also played a role, Phillips suggests. When female
koalas are in heat, their ovaries release the sex hormone estrogen,
which triggers mating behavior—whether or not males are present. This
hardwired urge to copulate, even if expressed with a female partner,
might be adaptive. “The homosexual behavior preserves sexual function,â€
Phillips says, enabling an animal to maintain its reproductive fitness
and interest in sexual activity. In males, this benefit is even more
obvious: homosexual behavior stimulates the continued production of
seminal fluid.
A lack of opposite-sex partners is also thought to help explain the
prevalence of homosexuality among penguins in zoos. In addition to
several gay penguin couplings in the U.S., 20 same-sex penguin
partnerships were formed in 2004 in zoos in Japan. Such behavior “is
very rare in penguins’ natural habitats,†says animal ecologist Keisuke
Ueda of Rikkyo University in Tokyo. Thus, Ueda speculates that the
behavior—which included both male pairings and female couplings—arose
as a result of the skewed sex ratios at zoos.
Researchers have found still other reasons for homosexual behavior
in domesticated cattle—which is such a common occurrence that farmers
and animal breeders have developed terms for it. “Bulling†refers to
male pairs mounting, and “going boaring†is its female counterpart. For
cows, the behavior is not just a stress reliever. It is a way to signal
sexual receptivity. The females mount one another to signal their
readiness to mate to the bulls—which, in captivity, may cause a breeder
to know when to bring in a suitable opposite-sex partner.
Homosexual
mounting is much rarer among cattle in the wild, Phillips asserts,
based on his research on gaurs in Malaysia, a wild counterpart to
domesticated cattle. “Cattle evolved in the forest, so a visual signal
was not going to be useful for them,†he says.
Stress and the greater availability of same-sex partners may
similarly contribute to the practice of homosexual acts among
self-described heterosexual humans in environments such as the
military, jails and sports teams. In a study published this year in the
journal Sex Roles, Anderson found that 40 percent of 49 heterosexual
former high school football players attending various U.S. universities
had had at least one homosexual encounter. These ranged from kissing to
oral sex to threesomes that included a woman. In team sports,
homosexuality is “no big deal and it increases cohesion among members
of that team,†Anderson claims. “It feels good, and [the athletes]
bond.â€
In stressful same-sex environments such as prisons or a war zone,
heterosexuals may engage in homosexual behavior in part to relieve
tension. “Homosexuality appears mostly in social species,†Böckman
says. “It makes flock life easier, and jail flock life is very
difficult.â€
Altered Spaces
In recent decades zoo officials have tried to minimize the stresses of
captivity by making their enclosures more like animals’ natural
habitats. In the 1950s zoo animals lived behind bars in barren
enclosures. But since the late 1970s zoo homes have become more
hospitable, including more open space, along with plants and murals
representative of an animal’s natural habitat. The Association of Zoos
and Aquariums (AZA) regulates everything from cage dimensions to animal
bedding. The AZA also outlines enrichment activities for captive
creatures: for instance, two golden brown Amur leopards at the Staten
Island Zoo regularly play with a papier-mâché zebra, an animal they
have never seen in the flesh.
Researchers hope such improvements might affect animal behavior,
making it more like what occurs in the wild. One possible sign of more
hospitable conditions might be a rate of homosexuality more in line
with that of wild members of the same species. Some people, however,
contest the notion that zookeepers should prevent or discourage
homosexual behavior among the animals they care for.
And whereas captivity may engender what appears to be an unnaturally
high level of homosexual activity in some animal species, human
same-sex environments might bring out normal tendencies that other
settings tend to suppress. That is, some experts argue that humans,
like some other animals, are naturally bisexual. “We should be calling
humans bisexual because this idea of exclusive homosexuality is not
accurate of people,†Roughgarden says. “Homosexuality is mixed in with
heterosexuality across cultures and history.â€
Even Silo the penguin, who had been coupled with Roy for six years,
displayed this malleability of sexual orientation. One spring day in
2004 a female chinstrap penguin named Scrappy—a transplant from
SeaWorld in San Diego—caught his eye, and he abruptly left Roy for her.
Meanwhile Roy and Silo’s “daughter,†Tango, carried on in the tradition
of her fathers. Her chosen mate: a female named Tazuni.
This story was originally printed with the title, "Bisexual Species".
good article. thanks.