"It's 'natural' selection.
...
Elephants and their ancestors have roamed the African continent for millions of years. They are the largest land animals on earth and can live up to 70 years. Despite an international ban on the ivory trade and other laws to protect elephants, their overall populations continue to fall due to habitat loss and rampant poaching for their tusks. Because of that, a once rare trait is being passed onto more African elephants. The trait is tusklessness, The loss of tusks is only the beginning. The real devastation occurs with the loss of a groups matriarch. The oldest and most experienced grandmothers are the family’s living memory of migration routes, friendly elephants, food and water sources, etc. Matriarchs are also, the first in line to protect their families and without them an entire group of elephants can fall apart..."