Nature Notes: Our Differences

Sexual dimorphism
Of all the vertebrates, birds exhibit the showiest sexual dimorphism, as seen at the Nature Trail in East Hampton Village, where the colorful male wood duck and mallard outshine their female counterparts. Durell Godfrey

In biology there is something known as sexual dimorphism; the two sexes are different in one or more ways. It even applies to some insects such as the swallowtail butterflies. Almost all vertebrates exhibit some form of sexual dimorphism. It is easy to tell us humans apart; girls and women just look different from boys and men. But it isn’t that easy for many other mammalian species.

Male members of the deer family have antlers, but some female members, say caribous, also sport them. The male lion has a bigger head than the female and more fur on it, including a furry mane on the neck. However, it’s not so easy to tell a male cheetah from a female cheetah, or a male leopard from a female leopard, or a male cougar from a female cougar. Even common house cats are difficult to tell apart by the naked eye.

Almost all male frogs and toads have a gular pouch, which they fill with air to use as a sound chamber in order to amplify a mating call. Otherwise, except for size differences, the sexes are very hard to tell apart. In some snake species, the males are more colorful than the females. In box turtles the bottom shell, or plastron, is concave for mounting the female’s conical carapace. Even so, during the reproductive act the male has a very slippery perch and often falls off backward while still attached to the female.

Of all the vertebrates, birds exhibit the greatest degree of showy sexual dimorphism. Such color variation is carried to extremes in warblers, ducks, pheasants, and many tropical rainforest species. Take the local wood duck: The male is about as colorful as any other male waterfowl, except perhaps the mandarin duck of Asia. 

The famous Big Duck monument on the side of the road in Flanders is all white, and so were the famous Long Island ducks, both males and females, that were sold there in the distant past. You can hardly tell the male geese and swans from the females, while male mallards, mergansers, buffleheads, shovelers, and teal easily stand out from their female mates. Sparrows are much less colorful and in song sparrows, it is hard to tell a male from a female, except when the male is singing. In fox sparrows, which are settling in now to spend most of the winter locally in the manner that hermit thrushes often do, the males are almost identical in color to the females, except a bit brighter.

The duller colors of female birds may protect them better from predation. It only takes a few males to service females, as in the red-winged blackbirds, which practice polygyny: The male courts and copulates with more than one female. Take our wild turkeys: Except for the absence of a wattle, females look very much like the males. Both female and male turkeys are very big birds and are not easy to predate. 

Both male and female cassowaries of New Guinea and other south sea countries and islands are very colorful and hard to tell apart. This nonflying species is second only to the ostrich in size and can defend itself with its specialized knife-blade middle toes. Yet the ostrich male’s plumage, while not as showy as the cassowary’s, is bicolored, dark on light, making it easy to distinguish from the female. The difference between the two species might have to do with their difference in preferred habitats — the cassowary is a creature of the dense rain forest, while the ostrich struts its stuff on the plains.

Fish, on the other hand, are puzzling. It’s hard to tell the sexes of the brilliantly colored coral reef fishes, and most of our coastal species — though not nearly as colorful as those first named — are also difficult to tell apart by sex. Fish such as striped bass, bluefish, pompano, bonito, mackerel, and menhaden that travel in large schools are similarly hued, whether male or female. In a nonschooling fish group, on the other hand, male members of the stickleback family are more colorful than females, especially when breeding. The colors, as in birds, are somewhat dependent on the male hormone testosterone.

While at the University of California Santa Barbara I studied the midshipman, Porichthys notatus. Their common name comes from the array of photophores along their sides, which resemble midshipman rows of buttons. These photophores light up when the fish is agitated and during reproduction. The females have photophores, but are reticent to use them. The males make long monotonic hums as long as 60 minutes or more that can be heard from above the water’s surface, while the females can grunt but are mostly silent. Thus, midshipmen exhibit two different forms of sexual dimorphism. In some species, Homo sapiens, for example, the males and females differ in many ways.

Sexual dimorphism is found in a high degree in the apes, especially in the human ape. It has become advanced in Western civilization to the degree that sexes in humans can be differentiated by appearance including dress, speech, gait, size, and body shape. The emphasis on sex appearance is, up until lately at least, found more in the female sex than the male one. The fashion business is largely built around female preferences, and there are a number of magazines built around these, almost all of which stem from corporations run mostly by men, so the emphasis on fashion and attractiveness is a kind of pandering by men to women. In many third world cultures, however, females are much less showy in dress, cosmetics, language, and the like. Some third world countries are following the same model, thus you have Bollywood from India, a spinoff of Hollywood.

But change is in the air as we see in the wake of the #MeToo movement. Even in Muslim countries women are beginning to free themselves from constraints imposed upon them by men and their religion. I am optimistic.

On the other hand, I don’t know what we can do about men, especially, the Caucasian kind. They’ve had it their way so long, they don’t know whether they are coming or going. They are still in charge, however, and, presumably hanging on until their knuckles turn bare. What will we do if the women leave us to fend for ourselves? That may become the conundrum of the century, even bigger than the global warming conundrum. 

Larry Penny can be reached via email at