It’s no secret that human activity can have a strong influence on the environment, but the ways in which we affect the evolution of animals around us can be more subtle. Now, new research has found that, for a population of African elephants (both species of which are now listed as endangered) in Mozambique, poaching proved to be a significant enough evolutionary pressure as to make natural selection favor tusklessness over animals bearing the adapted teeth that are so hotly sought after in the illegal wildlife trade.

The research, published in the journal Science, looked specifically at the influence of ivory poaching during the Mozambican Civil War, which spanned 15 years from 1977 to 1992, on a group of African savanna elephants (Loxodonta africana) in Gorongosa National Park, Mozambique. It was considered to be a period of particular interest in studying the potential effects of wildlife exploitation on evolution, as warfare has historically been associated with an increase in poaching in countries across Africa. 

The researchers used field and survey data as well as historical video footage and contemporary sighting data to assess how the war impacted the park’s elephant population. During the 15-year-war, the conflict took an enormous toll on the Gorongosa National Park’s large herbivores in general as populations dipped by 90 percent. With armies on both sides taking the opportunity to hunt for ivory, the population of African elephants began to shrink rapidly and as it did the researchers noted a threefold uptick in tuskless female elephants, from 18.5 percent to 50.9 percent.

The study authors took a deeper look to try and ascertain why this might be and found survey data that indicates a specific genotype was pivotal in tusk-inheritance patterns. There were two potential culprits: AMELX and MEP1a, both of which play a role in mammalian tooth development.

AMELX is a particularly curious candidate for two reasons. First of all, it’s an X-dominant, male-lethal trait, which means that male fetuses are unlikely to survive pregnancy as, unlike females, they don’t have a second X chromosome to counteract the AMELX loci. Secondly, in humans it’s known to hinder the growth of maxillary incisors (the tooth most comparable to elephant tusks), potentially providing a mechanism through which genetic changes within the population saw an uptick in tuskless females.

“Understanding the evolutionary consequences of wildlife exploitation is increasingly important as harvesting becomes more efficient,” the study authors write. “This study provides evidence for rapid, poaching-mediated selection for the loss of a prominent anatomical trait in a keystone species.”