Reader John O’Neall called my attention to a new article in The Independent about the continuing slaughter of African elephants for their ivory tusks. This is a form of artificial selection—the elephants targeted are those with the largest tusks—that has a predictable result given that artificial selection on a trait almost never fails:
An increasing number of African elephants are now born tuskless because poachers have consistently targetted animals with the best ivory over decades, fundamentally altering the gene pool.
In some areas 98 per cent of female elephants now have no tusks, researchers have said, compared to between two and six per cent born tuskless on average in the past.
. . . About 144,000 elephants were killed between 2007 and 2014, leaving the species at risk of extinction in some areas. Meanwhile those African elephant populations that do survive could become virtually tuskless, like their Asian cousins, researchers have warned.
Joyce Poole is head of the charity Elephant Voices and has been tracking developments in the species for more than 30 years. She told The Times she had seen a direct correlation between the intensity of poaching and the percentage of females born without tusks in some of the herds she monitored.
In Gorongosa National Park in Mozambique, 90 per cent of elephants were slaughtered between 1977 and 1992, during the country’s civil war. Dr Poole said that because poachers disproportionately targetted tusked animals, almost half the females over 35 years of age have no tusks, and although poaching is now under control and the population is recovering well, they are passing the tuskless gene down to their daughters: 30 per cent of female elephants born since the end of the war also do not have tusks.
You can read a longer and more scientific article about this at the African Wildlife Foundation. When I read about a “tuskless gene” in the bit above, I was dubious, for such selection will work regardless of its genetic basis, and traits like tusk size are usually influenced by many genes of smaller effect. But it turns out that, according to Poole, there is such a gene:
“Elephants carry a sex-linked gene for tusklessness, so in most populations there are always some tuskless elephants,” says Poole. “Because males require tusks for fighting, tusklessness has been selected against in males and very few males are tuskless. For African elephants, tuskless males have a much harder time breeding and do not pass on their genes as often as tusked males.”
I don’t know much about that gene, but it would seem to be recessive, so that tuskless males will always pass on the gene to their daughters, but not their sons (the gene is on the X, not the Y). Tuskless females would have to carry two copies of the recessive gene, and all their sons would be tuskless. But regardless of the genetics, selective poaching of elephants with bigger tusks will cause tusklessness to spread in the population.
You might think that this is fine: that once all the elephants are virtually tuskless, the poaching will stop, for elephants are killed only for their ivory. But it’s not that simple, for tusks are there for a reason: they’re used for self-defense, for digging, and, perhaps most important, females prefer to mate with males having larger tusks. While tuskless elephants may survive without their armaments, a strong female preference for mating with tusked males might mean that such populations simply won’t mate, and that means extinction.
This is not the only case in which artificial selection through hunting has changed a species: many edible fish, for example, have evolved reduced body size because fisherman not only go after the big ones, leaving the smaller ones to breed, but overfishing imposes selection on fish to breed when younger and smaller (those fish with genes allowing them to breed when younger are more likely to leave their genes to the next generation).
What we have, then, is another example of the efficacy of artificial selection, something that we’ve known for decades. (In fact, I know of only three laboratory selection experiments that have failed to change a population, and two of those are mine.) And the effect is predictable. The solution is not to cut the tusks off living elephants to prevent their slaughter, or to let elephants evolve tusklessness, which could lead to their extinction.) The solution is to stop the ivory trade. Steps have been taken to do this, but so long as ivory is coveted in countries like China, driving the price of tusks to stratospheric levels (a pound of ivory can fetch $1500 on the black market; a huge amount given the weight of tusks), the problem will persist, and we’ll see horrible scenes like this: