"We have seen aggressive behavior from elephants, but that's a story of the past."

Sometimes called white gold, the best ivory came from African elephants.

The technique had been applied to ivory from individual elephants, but the new work uses statistical methods to apply it across a group.

He said the ivory came from elephants who died natural deaths and was donated by farmers.

People should remain at least 50 metres from wild elephants, he said.

He discussed the question of whether or not the remains were from elephants, but drew no conclusions.

The goal was to educate Americans that ivory products come from elephants.

The old zoo, he says, "exhibited everything from elephants to lizards.

"They have lifelong family relationships-we could learn a lot from elephants."

There is a first gate with spikes to prevent attack from elephants.