A recent Scientific American post on lethal chimpanzee violence has me mulling over an incident that took place two summers ago when I was surfcasting for bluefish on Nantucket Island. My younger brother Matt and I were fishing on Great Point, a sandy spit protruding from Nantucket's northern end. I was hurling my fluorescent orange lure out into the white-capped waves and yanking it in when Matt, who was 20 feet or so to my left, shouted exultantly, "Got one!"

My brother and I are, shall we say, competitive. I love whipping him in tennis or catching more blues than him. So naturally I felt envy as he reeled his thrashing fish in, right across my line of sight. Then, something happened that I had never seen in a half century of fishing on Nantucket. A great gray beast lunged out of the sea, seized Matt's bluefish in its mighty jaws and plunged beneath the waves. I heard Matt's line race out with a whine and ping as it snapped. "Did you see that?!" Matt bellowed.

I laughed, naturally, not only because Matt's prize had been snatched, literally, away from him, but also because his reversal of fortune had been so delightfully dramatic. A seal had stolen his fish! I chortled again five minutes or so later when Matt, still muttering, tossed a new lure into the sea. A hirsute, whiskered head bobbed to the surface and remained there, looking at us. The seal was waiting for us to hook another meal.

Reports of gray seals—which can weigh as much as 800 pounds—stealing hooked bluefish and stripers off Cape Cod and Nantucket surfaced in 2008. The tactic makes sense. Bluefish are fast, but a seal can easily grab a hooked fish. Within a year, seals were filching fish as far away as Long Island Sound, 200 miles south of Cape Cod. Some seals are remarkably brazen. A YouTube video shows a gray seal lumbering onto a beach to snatch a fish that a man had already landed. "What the hell!" the fisherman yells as the seal, fish in its jaws, lunges back into the sea.

The seals' predatory hunger for fish, it occurred to me later, is instinctual, an innate, inherited, adaptation, but their larceny is learned. A clever seal got the idea of stealing fish hooked by humans, and other seals, after observing his success, started imitating him. This cultural innovation, or meme, spread.

So what does the thievery of seals have to do with the violence of chimps? Here's what. Over the past few decades, scientists have observed dozens of incidents in which male chimpanzees banded together and killed chimps from neighboring communities. According to a recent study by anthropologist Michael Wilson, reported on by Kate Wong, males from one group carry out raids when they can do so with little risk to themselves. "This tells us something about human evolution," Wilson said.

Wilson was alluding to the claim of anthropologist Richard Wrangham—set forth in his book Demonic Males (Houghton-Mifflin, 1996, co-written with journalist Dale Peterson)—that the roots of human warfare extend back millions of years, all the way to the common ancestor that we share with chimpanzees, our closest genetic relatives. The biologist Edward Wilson expresses support for Wrangham's theory in his new book, The Social Conquest of Earth (W.W. Norton, 2012). So does another Harvard scientist, psychologist Steven Pinker, in his book The Better Angels of Our Nature (Viking, 2011).

The evidence simply doesn't support the claim that chimp raids and human wars stem from ancient, innate adaptations. As anthropologist Brian Ferguson pointed out last year in a stinging critique of what he called "the myth of innate depravity," scientists did not observe a lethal chimp attack until 1974, 14 years after Jane Goodall started watching chimps in Tanzania. Chimp raids are rare; according to one estimate, a typical community carries out a raid every seven years. Some communities have never been observed engaging in intergroup raids.

Nor, as Wong noted in her post, have bonobos ever been observed killing each other. Bonobos, whose formal name is Pan paniscus, are just as closely related to Homo sapiens as the more common chimpanzee species Pan troglodytes. Why is it the violence of Pan troglodytes, and not the peacefulness of Pan paniscus, that, in the words of Michael Wilson, "tells us something about human evolution"?

The oldest evidence of lethal group violence among humans is a mass grave about 13,000 years old found in the Sudan, and this site is an outlier. The vast majority of evidence of human warfare is less than 10,000 years old. And although human history has been wracked by warfare, many societies, both prehistoric and modern, have avoided mass violence. Excavations have revealed that people settled in Abu Hureya, near the Euphrates River, 11,500 years ago, and lived there for millennia while leaving no signs of violence. Switzerland and Sweden have maintained their neutrality for the past two centuries even when wars raged around them. All this data is consistent with the view of war as a meme, or an "invention," as anthropologist Margaret Mead put it—just like seals' theft of hooked fish.

What about my compulsion to beat my brother when we are playing tennis or fishing? Or my love of victory and hatred of losing when I play hockey? My competitiveness is probably innate, inherited from my father. But just because many males are competitive, even aggressively so, doesn't mean that we are, as Wrangham has claimed, "natural warriors," who kill if we think we can get away with it. The sooner we reject this pernicious meme, which gives us an excuse for our warlike behavior, the better.

Photo credit: Seabird Ecological Assessment Network (SEANET).