It’s probably the only thing that will save them from poachers. Both sides in the civil war in Mozambique (1977–1992) slaughtered elephants to finance their war efforts. Before the war, only a fifth of females lacked tusks. After the war, half did, likely due to differential survival rates:
After the war, those tuskless surviving females passed on their genes with expected, as well as surprising, results. About half their daughters were tuskless. More perplexing, two-thirds of their offspring were female…Christina Larson, “Why no tusks? Poaching tips scales of elephant evolution” at AP News(October 21, 2021)
A bit of sleuthing later:
Because the tuskless elephants were female, they focused on the X chromosome. (Females have two X chromosomes; males have one X and one Y chromosome.)
They also suspected that the relevant gene was dominant – meaning that a female needs only one altered gene to become tuskless — and that when passed to male embryos, it may short-circuit their development.
“When mothers pass it on, we think the sons likely die early in development, a miscarriage,” said Brian Arnold, a co-author and evolutionary biologist at Princeton.
Their genetic analysis revealed two key parts of the elephants’ DNA that they think play a role in passing on the trait of tusklessness. The same genes are associated with the development of teeth in other mammals.Christina Larson, “Why no tusks? Poaching tips scales of elephant evolution” at AP News(October 21, 2021)
Overall, tusklessness is not an advantage to elephants except that, unusually, the alternative is extinction. The pattern points to tusklessness as a good example of devolution, the dropping of an overall useful trait because, in a specific difficult situation, it endangers survival.
You may also wish to read: Devolution: Elephants survive by shedding their tusks
Devolution: Getting back to the simple life