Sex differences

Steve Stewart-Williams

Without further ado, then, here are ten of the most common sex differences found in the animal kingdom.

1. In many species, males and females differ in size. In most, the females are larger. Among spiders, for instance, the males are often microscopic compared to the giant females. Among large vertebrates, on the other hand, the size difference is often reversed, and males are the larger sex. Thus, male gorillas are twice the size of females, and bull elephant seals are three or four times the size.

2. Males in many species have a stronger sex drive than females, and a more powerful appetite for new and numerous sexual partners. This reveals itself in many unexpected ways. Male fur seals have been observed trying to mate with king penguins; male snow monkeys have been observed trying to mate with deer; and male jewel beetles have been observed trying to mate with beer bottles that vaguely resemble female jewel beetles. Even more jaw-dropping, a male mallard duck was once observed raping a fellow male who’d recently flown into a window, dying on impact. All these examples show that the male sexual response can be rather indiscriminate, to put it politely.

3. The flipside of this coin is that females are often much choosier than males about their sexual partners. A common sight in nature is a hapless male trying desperately to impress a female, and the female turning away, completely uninterested. Another common but less amusing sight is a male violently trying to force a female to mate with him, and the female trying desperately to escape. Both cases illustrate females’ greater sexual choosiness.

4. Males are often more ornamented than females. The peacock’s tail is the standard example, but it’s only one of many. From birds to reptiles to insects, males in many species are adorned with head crests, throat sacks, or bright, patterned feathers, or have a repertoire of songs, dances, and other party tricks designed to impress the females.

5. In many species, males “pay” for sex. For example, among black- tipped hanging flies, an amorous male will present a female with a nice, juicy insect, and then copulate with her while she distractedly enjoys her meal. If the female finishes before he does, she simply walks away – game over. If, on the other hand, he finishes first, he snatches the insect away and tries to woo another female with the leftovers. In other species, the “payment” is less direct. Thus, in many birds, fish, and frogs, males maintain territories where the females lay their eggs and rear their young. In return, the males get to sire their offspring.

6. Males are generally more aggressive than females, and spend more of their spare time beating each other up. The prototypical examples, seen in a thousand nature documentaries, are male deer locking horns and bull elephant seals locked chest-to-chest in combat. But again, we find a thousand more examples in every corner of every continent. To begin with, male kangaroos routinely fight for females. The fights look a lot like boxing matches except that, unlike human boxers, the kangaroos periodically rear back on their tails and kick their opponents with both feet. Similarly, male ring-tailed lemurs engage in what are called “stink fights”: They impregnate their tails with their scent and then waft it at their opponents. If that fails to sort things out in a gentlemanly fashion, they then start violently jousting with each other. In these and other cases, the males are either fighting directly for females, or fighting for the resources, territories, or status that are needed to attract the females’ interest.

7. Males often come equipped with a frightening arsenal of built-in weapons. These include everything from antlers and spikes to supersized fangs. Males also often have built-in defenses, such as tough skin and reinforced skulls. Females, in contrast, are normally less well armed and less well armored.

8. In many species, females grow up faster than males, a phenomenon known as sexual bimaturism. In gorillas and elephant seals, for instance, females reach reproductive maturity several years before males. Likewise, among satin bowerbirds, females reach reproductive maturity at around two years of age, whereas males don’t reach reproductive maturity till around seven.

9. Females tend to live longer than males. Dawson’s bees are a memorable example. By the time the females of this Australian bee species lay and provision their eggs, all the males are dead – killed in a vicious struggle to fertilize as many females as possible. The end result is a society consisting solely of females.

10. Last but not least, in species where parents care for their young, females usually do most of the caring. Among tigers, for example, females are the primary caregivers, while the males are deadbeat dads. This is a fairly standard arrangement among mammals, and among parental animals in general.

Sex differences by Manuel Fraga is licensed under a Creative Commons Attribution 4.0 International License.

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