Bruce Bagemihl - Biological Exuberance

A phenomenon known as delayed implantation also enables males and females to spend long periods away from each other. In nearly 50 mammalian species (including seals, bears, other carnivores, marsupials, and some bats) the fertilized egg does not implant right away. It remains in “suspended animation” for several months, after which it implants and begins its regular development. The delay extends the pregnancy by two to five months in seals and up to ten to eleven months in badgers, fishers, stoats, and related small carnivores. In seals, this allows females to spend a longer time out at sea—often completely separate from males—and permits them to optimize the timing of their pregnancies and to take advantage of more favorable times of the year for birthing and pup-raising. Some species of bats also have delayed embryonic development, in which the fertilized egg experiences a temporary cessation of development after implantation. 102

In fact, delayed implantation as well as sperm storage (among a variety of other factors) effectively result in a separation and reordering of key reproductive events in many vertebrates, and consequently an “uncoupling” of male and female reproductive cycles. We are used to thinking of breeding as an ordered progression, one stage leading inevitably to the next: ovulation followed by mating followed by fertilization followed by pregnancy followed by birth (or egg laying). However, there are often significant gaps and rearrangements of these events: sperm storage can temporally separate mating from fertilization, while delayed implantation separates fertilization from fetal development during pregnancy. As noted above, sperm storage can also result in ovulation taking place after insemination, and in other animals, further rearrangements occur. In birds, for example, “pregnancy” or the development of the egg inside the mother’s body actually precedes fertilization: the egg yolks are already quite large (and may cause a noticeable bulge and weight increase in the female) prior to being fertilized. In fact, the eggs can be laid without ever being fertilized—this is what allows females in homosexual pairs to produce (infertile) eggs. In most fishes, “pregnancy” ends, rather than begins, with mating: the eggs develop within the female’s body and are then laid or discharged when ready to be fertilized (i.e., fertilization typically takes place outside the female’s body). 103In addition to these delays and reordering of reproductive events, breeding can also, of course, be interrupted or terminated at any of these stages—this will be discussed in the next section, when we look at naturally occurring forms of birth control.

Another common misconception about animal heterosexuality is that only females experience periodic hormonal fluctuations in their reproductive biology. In fact, many male animals also have sexual cycles, entailing considerable periods in which they are sexually inactive and living separate from females. Occasionally, male and female sexual cycles are poorly synchronized or not optimal for breeding, as sometimes happens in Ostriches and Lovebirds. Male cycles are found in a wide range of animals, including primates, deer, seals, and numerous bird species, and usually entail a yearly, rather than a monthly, periodicity. In some instances, dramatic physical and physiological changes are involved. Male Wattled Starlings, for example, undergo regular periods of “balding” (feather loss) and wattle development, and males of many other bird species develop dramatic nuptial plumages associated with breeding. Male Squirrel Monkeys become “fatted” during the peak of their sexual cycle, while male Elephants experience “musth,” involving a whole host of changes such as glandular secretions, increased aggression, and rumbling vocalizations.

The significance of male sexual cycles has often been lost or overlooked under sexist biological theories, which tend to emphasize aspects of animal biology that confirm the unflagging “virility” of male animals, to the exclusion of those things that underscore the similarities between male and female sexuality. In fact, reproductive traits that are usually thought to be exclusively male or female can be found in members of the opposite sex in at least some species. Male pregnancy occurs in sea horses, for example, while lactation—milk production from fully functional mammary glands—was recently discovered in male Dayak fruit bats. 104Females, for their part, can carry sperm within their bodies and “inseminate” themselves (as discussed above) or may possess elongated, phalluslike clitorides that can undergo erections (this is found in numerous mammals, including Spotted Hyenas, moles, and Squirrel Monkeys, as well as several flightless birds). 105Some animals (e.g., Seals, Bears, Squirrels) even have a clitoral bone, homologous to the male’s baculum or penis bone in these species; in female Walruses, this bone may be over an inch long. Female pipefish and Japanese sea ravens (a kind of fish) even have extendable genital organs used to penetrate or retrieve sperm from their male partners. 106

When males and females do manage to get together, a formidable set of obstacles often stands in the way of achieving sexual contact and, ultimately, reproduction. Refusal or indifference by either the male or female partner is widespread and routine in the animal kingdom, and heterosexual matings are often “incomplete” in the sense that they do not involve erection, genital contact, ejaculation, and/or insemination. In one study of Chaffinch heterosexual copulations, for example, every “complete” and “incomplete” mating attempt was logged: out of 144 attempts, only 75 (52 percent) involved mounting with full genital contact (and therefore could potentially have led to fertilization). Of the remaining “unsuccessful” attempts, 76 percent entailed no mounting at all because one or both partners fled before copulation could take place, 9 percent involved the male mounting without attempting to make genital contact, in 8 percent mounting was terminated when the female refused to continue (in some cases after being pecked by the male), in 5 percent of the mounts the male slipped off the female’s back, while in 1 percent of the cases the male mounted in a reversed head-to-tail position and therefore did not make genital contact. In African jacanas, only about one in four sexual solicitations by the female result in the male actually mounting her. 107In some species, completion of the sexual act is prevented because of interference from other animals, who actively harass males and females while they are copulating. This is typical of many primates, but has also been reported in some birds such as King Penguins, Kittiwakes, and Sage Grouse. 108

In a number of animals, it appears that male and female anatomy are not ideally suited to heterosexual interactions. The female Elephant’s vaginal opening, for example, is much farther forward on her belly than in other mammals. Although the male’s penis has a special shape and muscles that allow it to reach the female’s genitals, he still often experiences considerable difficulty in achieving penetration and may end up ejaculating on her anus or otherwise outside her body. Moreover, it is not true that male and female genitals always fit together like a “lock and key”: in many species the structural “compatibility” of the sex organs is less than perfect. In addition, the female’s internal reproductive tract in most animals is—in the words of several zoologists—a tortuous, obstacle-ridden pathway that is “remarkably hostile to sperm.” Its structure, chemical composition, and immune response to semen are actually designed to prevent most sperm from ever achieving fertilization, in part to protect the female from possible infection (sperm are, after all, “foreign” bodies) and in part to allow her to control paternity. 109Males and females may be anatomically incompatible in other respects as well. Biologists studying Musk-oxen have observed that the male’s build—a deep chest with short legs, and most of his considerable weight concentrated in the front half of his body—is decidedly ill-suited to mounting and clasping the female, and studies have shown that males are able to successfully mount females less than a third of the time. 110In many other species of hoofed mammals and seals where there is a significant size difference between the sexes, females often fall or are crushed under the weight of the male during copulation and may suffer serious (even lethal) injuries.