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medical school, I don’t think that’s a problem. If a person envies the peace and calm of a colleague from work and decides to takeup meditation and yoga to try to emulate those traits, great! Looking around to see what others have and then trying to get those things for ourselves is a basic part of how human society works. The fact that capuchins and dogs have envy might be the small cost that comes with all the advantages of being part of a social species.
    But envy does bad things sometimes too. And while theft is an obvious symptom, another one is infidelity. Think about it: coveting thy neighbor’s partner can sometimes lead to affairs, and that can cause serious emotional pain for everyone involved. Animals cheat even more than professional athletes do, and I have to think that envy plays a role for them at least some of the time.
    Take species with harems, for example, where you have a single male who gets to mate with a whole bunch of females. This always means that a bunch of other males have to sit on the sidelines and mate with no one. How could they possibly not be envious? My favorite example of this is the sac-winged bat I mentioned in the chapter on sloth, the ones I saw roosting outside my first vampire bat cave in Costa Rica and whose males are known for flinging feces and urine on the females they want to mate with. (Yes, those sac-winged bats.) So help me, if there’s envy surrounding sex in the natural world, that is a species that would have it. 16
    Male sac-winged bats have a lifestyle in which one male gets to be the partner to a harem of up to seven females. Those females live with one another, and with one another’s pups, on the side of a tree, cave, or building. Solitary males, called satellite males, roost nearby, without any females of their own.
    The sac-winged bat got its name from the pockets it has in its wings, just above its elbows. (Here’s where things get disgusting.)Right before heading out for a long night of hunting insects, a male licks out the sacs in his wings to clean them, then leans down, fills his mouth with his own urine, and spits that urine into his wing sacs. Next, he leans back down and rests his throat against his penis and quivers until a white droplet comes out of his penis and sticks to the fur on his chin. Then he transfers that droplet with his chin to the urine-filled wing sac, before repeating the procedure to fill the other wing sac.
    Mixed together, the urine, saliva, and genital secretions produce a musky bouquet of odor. The male then hovers in front of a female in his colony and shakes his wings at her, much like a person would shake a salt shaker at their food, thereby covering that female with a sample of his sexy cologne. This behavior is called salting.
    Males are advertising how healthy they are with the way they smell, and females use scent to decide whether or not the male is sexy enough to mate with. That’s why males have to clean their sacs out each day and make a new batch. Bacteria living in the sac constantly break down scent molecules, producing other, less attractive odors. To a female, those bacterial odors are a sign that the male isn’t quite up to snuff.
    Every once in a while, a satellite male will salt one of the females, giving her a sample of his wares (sometimes he’ll even salt the harem male!), but the harem male responds by chasing him back to the periphery, and salting on him for good measure.
    It’s pretty clear that the satellite males are just waiting for an opportunity to take over the harem. When researchers experimentally remove a harem male from his roost, it’s always a satellite male that takes his place, as opposed to a dominant male from another harem, for example. And it’s not just any satellite male.It’s a satellite male that had previously been sitting right at the periphery of that particular harem. Since there can be several harems close to one another on a wall, I think that’s suggestive that a