That's a very frightening number--4000 dead elephants from an estimated 500,000 elephants left in the entire world today. Putting that into perspective, it's like 56,000,000 people getting killed for their teeth.
They use their tusks to dig in the ground and pry bark off trees. And the tusks grow on formidable 7-ton beasts. And so I'm genuinely baffled how early humans discovered the utility of the elephants' tusks.
In more modern times ivories are made into piano keys. Today, piano keys are made out of plastics, but not before seriously denting the population of elephants worldwide; piano manufacturer Steinway discontinued its ivory keys in 1982. Yamaha attempted to create a surrogate for ivory in the 1980s by developing Ivorite, a substance made from casein (milk protein) and an inorganic hardening compound. The Ivorite was trumpeted as having both the moisture-absorbing quality of ivory and greater durability, though some of the first keyboards later cracked and yellowed, requiring refitting with a reformulated veneer.