PUBLISHED NOVEMBER 9, 2018 NATIONAL GEOGRAPHIC

The oldest elephants wandering Mozambique’s Gorongosa National Park bear the indelible markings of the civil war that gripped the country for 15 years: Many are tuskless. They’re the lone survivors of a conflict that killed about 90 percent of these beleaguered animals, slaughtered for ivory to finance weapons and for meat to feed the fighters.

Hunting gave elephants that didn’t grow tusks a biological advantage in Gorongosa. Recent figures suggest that about a third of younger females—the generation born after the war ended in 1992—never developed tusks. Normally, tusklessness would occur only in about 2 to 4 percent of female 

Decades ago, some 4,000 elephants lived in Gorongosa, says Joyce Poole—an elephant behavior expert and National Geographic Explorer who studies the park’s pachyderms. But those numbers dwindled to triple digits following the civil war. New, as yet unpublished, research she’s compiled indicates that of the 200 known adult females, 51 percent of those that survived the war—animals 25 years or older—are tuskless. And 32 percent of the female elephants born since the war are tuskless.

Though researchers are further investigating the genetics behind tusklessness, the trait appears to be sex-linked³. In the abovementioned field study, the 33% of female elephants aged 10–20 are presumably the offspring of tuskless mothers. No tuskless males were observed at Gorongosa². This is perhaps due to more selective pressure on males to have tusks; mate competition among males is violent and sometimes:deadly. If a male does not have tusks, he may be severely injured and at a disadvantage in fights. Male elephants seem to have a two-front war: mating pressure to produce more offspring, and poaching pressure that targets the largest pair of tusks. Though tusklessness is a rare trait linked primarily to a minority of the female population, those with tusks (male and female) are also changing in response to poaching pressure: tusk size itself is on the decline.

https://medium.com/elp-rumbles/changing-tusks-in-response-to-poaching-5751f3aad922

Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment.

Tuskless Elephants