Does Hunting Have a Bad Effect on the Gene Pool?

Like many misconceptions about hunting, “it stands to reason”: hunters (especially trophy hunters) take the biggest and most beautiful male animals, so only those with “inferior genes” are left to reproduce, and it leads to “degradation” of the species. There’s been lots of alarmist cries about this, and even many hunters are concerned about possible harm. The concern is justified because we’re responsible for our wildlife, but studies show that nature doesn’t work this way. James R. Heffelfinger reviewed all available evidence in a totally awesome paper and concluded that hunting, as a rule, can’t really damage the gene pool. For those who don’t really care for academic prose, we offer a simple English explanation in this blog post.

Let’s say you’ve got a sheep tag. We’re talking sheep because the only evidence that trophy hunting might have a negative effect on the gene pool comes from one herd of bighorns. You’ve climbed up the ridge with a commanding view over two valleys. You scope the one on the left and see a ram with a full curl. You scope the valley on the right and see another ram, with 1 1/4 curl. Both are the same distance from you, and equally hard to approach.

Which one you’re going to try for? Obviously, all other things equal, you’ll go for the second, bigger ram. This is called selection by hunting, and that’s where you’re supposed to be “damaging” the gene pool by removing “superior” animal. The question is, does the second ram really  have “better genes” than the first? And the answer is, not necessarily.

Size of the Trophy Does Not Only Depend on Genes.

There are many reasons why one animal’s horns or antlers are bigger than the other’s. One of the obvious ones is age. The first ram in our example may be only 6 years old, and the second one a 11-year-old veteran. The second ram is not getting any bigger, and the first has the potential to develop 1 1/2 or 1 3/4 curl horns a few years later. If you take the bigger and older ram, in this case, you’ll actually give the “genetically superior” ram a better chance to carry his genes over!

Food is also very important. Horns and antlers don’t grow out of thin air. To reach the max size “prescribed” by the animal’s genes, the animal must have unlimited access to the right nutrients. This especially matters for antlers, that are shed and grown again each year, but is important for all horned animals.

The first ram in our example could be growing up in a valley that had a limited amount of nutrients, because of overpopulation or other reasons. That’s why his horns have only grown to 60% of what they could be with his genes. Meanwhile, the second ram has come from an area with abundance of food, and his horns grew to say 90% of the “genetic maximum”. That’s why his “horn size gene” may be smaller than the first ram’s, but his horns be actually bigger.

As a matter of fact, it starts when the lamb is still in the ewe’s womb. Conditions under which the mothers live, how much nutrients they have available, and even how much stress they experience, are very important. Studies confirm the self-evident truth that mothers who live better produce offspring with bigger bodies, and bigger horns and antlers (if any). And mothers can influence their offspring’s development in more ways than one!

Cherchez la Femme, or, It’s Not Only a Man’s World!

All right, so trophy hunters “select” male animals. But what about females? As we all know, it takes two to tango, and all mammals get two sets of genes: one from the mother, one from the father. Question: where does the “horn size gene” come from? There were experiments made on captive white-tailed deer, and… surprise, surprise! It looks like the gene comes from the mother’s side! That means that no matter how many big-antlered bucks you remove from the population, the next generation will still get the “big antlers gene” from their moms!

It’s not yet clear whether in other ungulates the gene of horn or antler size is inherited from the mother’s set, from the father’s set, or any at random. But in most of these species females outnumber males 2 or 3 to one, so hunters’ selection acts only on ¼ or ⅓ of the population. That doesn’t make it very efficient, does it?

Mating Matters.

We look at the majestic elk or red stag, and their harem of maybe a dozen cows, and think that only alpha males sire offspring. If you look closely, however, it turns out that about a third of the females cheat on their dominant “husband” with subdominant adolescents. In bighorn sheep herds, almost a half of lambs are sired by subdominant males. That means that best rams begin to pass their genes before they are big enough even to be legal harvest, much less interest a trophy hunter. From the gene pool perspective, it doesn’t matter if these rams will be killed in their first season of maturity; their genes stay in. And don’t forget that in most cases it’s the females who choose whom to mate, not the other way round.

Wilderness is not a farm. Where deer are kept as cattle, and the breeders have full control over who mates with whom, everything is possible. They could breed deer with insanely huge antlers, or they could breed totally antlerless deer, or deer with any antler shape. But as long as the animals have the choice who to mate, selection by humans have a very limited effect. If you have a game ranch, and cull a third of the bucks with smallest antlers, you won’t see any increase in antler size. Especially if your population is not isolated – and few free-range herds are isolated. Usually there’s enough migration to bring in fresh genes. That’s why wildlife refuges, where hunting is not allowed, are so important – when hunters harvest animals with supposedly “superior genes”, new ones move in to restore the gene pool.

Hunters Aren’t Really That Selective.

It’s not like the guide lines up all legal rams in the neighborhood before you, hands you over the printouts of their gene tests, you choose one and shoot it. Of course, some trophy hunters may be pickier about what animal they bag than a show biz star about the dress to wear to the Academy Awards ceremony. But even in a perfect trophy hunting scenario – like our example with two rams – there’s a limit to selectiveness. If it’s the last day of the season and a once-in-a-lifetime tag, you’ll go for the one that appears easier to get, even though it may be the smallest of the two. And there might be an even bigger one behind the ridge that you’ll never know about.

In any case, trophy hunters make up a very tiny minority of North American outdoorspeople. According to surveys, only 1 to 3% of American hunters deliberately try to bag only the animals that have the best trophy characteristics. The remaining 97% are happy with any legal animal, and those range widely from does and spikes to minimum sized mature bucks, depending on species and regions. Don’t forget that even trophy hunters often have to take a not-quite-the-best animal or go home empty-handed. With this in mind, the “selection” effect of hunting, for most big-game species in most environments, is about zero.

But We Must Watch Out Nevertheless!

Human impact on the gene pool is very limited. The “natural” selection factors, such as predation and disease, play a much more important part in it. There’s been roads and cars for more than thirty deer generations, but the roadkill-proof deer hasn’t evolved yet.

But that doesn’t mean hunting is completely harmless. If we take a small, isolated herd of wild sheep, and if we do our best to kill every ram that grows a 4/5 curl or bigger rack, and if we continue to do so for a long time, the sheep in that herd might evolve into a no-curl sheep species.

The chance of it happening is very, very slim – but it is one of the reasons why we need science-based hunting regulations. And don’t forget it was hunters who first suggested the concept of fair chase, wildlife sanctuaries, and all other things that make sure our heritage and the animals we love, will pass over from generation to generation.