This is not a column about how we should regulate the possession of firearms in this country.
Nor is this a column about the human tragedy of gun-related violence, despite the many examples.
Instead, this is a column about how guns — and other means of hunting and fishing — control wild animal populations, from the basics of their size and distribution, to the subtle but profound carry-overs into evolutionary time.
As long as we have been Homo sapiens, we have been predators. Certainly, our diets have always been mixed, taking advantage of whatever bounty nature provided, including large portions of plant matter like fruits, tubers, even the bark peeled from trees. But the protein of other animals played — and continues to play — an important role in our diet.
Today, most of our protein comes from livestock reared on farms specifically for our consumption. Yet the omnivores among us may also consume animals harvested from the wild: fish like cod, tuna, or salmon; the occasional cut of venison. (Despite my own forays into vegetarianism, I find all of the above delicious.)
We occasionally hear disturbing tales of how our harvest of natural populations may be unsustainable. The majority of our industrialized fisheries are in decline or collapse. The bush meat trade decimates wildlife in South America and Africa.
If we need any evidence that human predation can drive other species to the brink, we need look no further than North America, where the first human inhabitants likely hunted many large mammals (think woolly mammoth, etc.) to extinction.
Yet we often do not hear about another process that results from our harvesting efforts: so-called unnatural selection.
Unnatural selection is artificial selection’s accidental cousin. Artificial selection occurs when humans deliberately breed animals (or plants) with the traits that we desire, so that subsequent generations will have them. Artificial selection gave rise to exceptionally milky cows, impressively woolly sheep, a plethora of bizarre looking dogs and cats, and even Darwin’s (r)evolutionary insights.
Artificial selection is something that we do deliberately. Unnatural selection is something we do accidentally – a consequence of preferentially capturing wild animals with certain traits, leaving the remainder of the population in the wild to breed.
There are an increasing number of examples of unnatural selection, both in populations that we harvest at large commercial scales for food, and in those we hunt for sport.
Among the latter, studies in Canada have shown that bighorn sheep horns are getting smaller. This happens because trophy hunters kill the rams with the most impressive racks. Thus, individual sheep with smaller horns are more likely to survive and reproduce, passing their diminutive genes on to the next generation. In Africa, the (illegal) ivory trade produces a selection pressure so strong that tuskless elephants are on the rise.
At the commercial scale, larger fish have more market value, so we arrange our gear to preferentially catch them. Over time, scientists have observed a shift in cod reproduction: these (relatively) long-lived fish now begin reproduction at a younger age and smaller body size.
These may read as interesting facts, but they also have important evolutionary consequences. There’s a reason that rams have horns: They joust with them for the right to mate, and as you might guess, rams with bigger horns are tougher, more fit, and more likely to win, passing on their genes and improving the robustness of the entire population. Similarly, bigger codfish produce more young of higher quality, improving the fitness of the entire population, and its odds of surviving extinction over the long course of evolutionary time. By selectively removing the healthiest individuals, we leave behind breeders whose offspring will be more poorly adapted to their environment.
All this is not to say that I am opposed to hunting and fishing.
I would even argue that human hunters should to play an important role in the control of certain animal populations. For example, deer are overpopulated in many parts of the United States. In this case, hunting can serve the dual purpose of population control and putting food on the table. (Did I already mention that I find deer delicious?)
But we must show the same awareness in our harvesting practices that we have displayed in our breeding programs. We must consider what it means to harvest the strong, the big-antlered, the large-bodied. We have seen compelling evidence that we are producing selection pressures that, at times, run counter to those that these organisms would experience in our absence. It’s important to consider what this means for their survival in the long run.
Holly welcomes questions, comments, and venison burgers from her readers. She can be reached via email at hollyvm “at” stanford.edu.