The world can be divided into two categories: The haves and have-nots.

The same is the case in nature and, more specifically, in mammals. In the group of haves, you will find many species of primates (but not spider monkeys), rodents (minus the lagomorphs or rabbit family), moles, shrews, hedgehogs, bears, cats and dogs, walruses, seals, sea lions, raccoons, otter, bats, weasel and skunk, among others. These species can hold their heads high.

Humans, whales, dolphins, elephants, those rabbits and spider monkeys, porpoises, marsupials, monotremes, and those in the equid (horse family) are among the have nots.

Allow me to explain.

What some lack and others possess is the baculum. The baculum is a bone, or more specifically, a penis bone. The word bacula is derived from a Latin root translated as “stick” or “staff,” and is also known as an os priapi. Dig deeply into etymology and all will be clear. Priapus is the God of Fertility, who was the son of Aphrodite (Goddess of love) and Dionysus (God of wine). Priapus is the rustic God of gardens, livestock, plants, fertility, and male genitalia. He has been described, not so kindly, in the literature as a “grotesque little man with a large phallus.”

Hot debates rage about the function of the bacalum. Some scientists note that this bone allows for short, quick encounters. Animals with a baculum can be ready faster and produce the required result more rapidly than a male without a bacalum, who needs to rely on slower increases in blood pressure for the same outcome.

While animals have their reproductive uses for the baculum, humans have found various other functions for a bacalum retrieved from an animal carcass. One Native Alaskan culture called the bacalum “oosik” and employed it as a handle for knives and tools. People have been known to wear this bone as a fertility or luck charm. Some suggest, perhaps or perhaps not in jest, that the bacalum can function as a coffee stirrer or mountain man toothpick, depending, of course, on the species from which it came and the space between your teeth.

This leads to a discussion, not surprisingly, of size. Some studies have showed no correlation between the size of adult male animals and the size of their baculum. Case in point, a 350-pound gorilla’s baculum measures less than half an inch, whereas a raccoon boasts a four inch baculum. Massive is the baculum of the walrus, measuring up to 30 inches. And the bone can be valuable, too. In 2007, the baculum of an extinct species of walrus sold for $8,000.

One last note: Females are not necessarily categorized as have-nots, either. Some species have a bone homologous to the baculum called the baubellum, or os clitoris.

It seems to be a mere roll of the evolutionary dice that determines which species were endowed with these specialized bones. It could be argued that the have-nots may have a bone to pick with those on which a baculum was bestowed, or to put it in simpler terms, they got stiffed.

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown.