Great apes, humans' closest relatives, are nearing extinction and people should fear losing the biological knowledge that would die along with them, a primatologist says.

Craig Stanford, co-director of the Jane Goodall Research Center at the University of Southern California, says that four types of great apes — chimpanzees, bonobos, gorillas and orangutans — may become extinct within the next century.

In his new book, Planet Without Apes, Stanford writes that this is a result of habitat loss, poaching, a bush meat black market, disease and political instability.

In an interview that airs Saturday on CBC's Quirks & Quarks, he says humans share the majority of their DNA sequence with great apes, specifically chimpanzees and bonobos, with only a handful of differences in their genetic makeup.

"We're obviously made of the same fabric," he said. "We're made of the same cloth, and when we look at them, we are seeing ourselves."

Losing the great apes would also mean losing the opportunity to learn more about humans.

Great ape population in 'precarious' situation

People do not initially believe his contention that the great ape population is in danger, he says, because their total current numbers sound high.

According to the World Wildlife Fund there are:

100,000 to 200,000 gorillas

150,000 to 250,000 chimpanzees

10,000 to 50,000 bonobos

About 48,500 orangutans.

Stanford said he compares the great apes' plummeting populations to the human population — seven billion and growing.

Only then, he said, do people "realize how precarious their situation is, how close they truly are to slipping off the edge."

Bush meat black market problematic

The ape population has struggled for many reasons, including habitat loss, poaching and a bush meat black market.

Great ape meat is considered a delicacy in certain regions of Africa, said Stanford. Some people kill great apes for commercial purposes, he said, smuggling the meat into cities where there is a cultural taste for bush meat.

The World Wildlife Fund estimates there are only 10,000 to 50,000 bonobos, such as this baby bonobo at a German zoo, alive in the world. (Michael Probst/Associated Press)

Tonnes of bush meat are shuttled to Brussels, Paris, New York and London and sold on black markets each year, he said. Most of it comes from smaller animals, like antelopes and pigs, he said.

But any amount of industrial-level hunting and harvesting cannot be sustained by the great ape population, which is very slow to reproduce, he says. On average, a female gorilla will give birth once every four to six years, according to the WWF.

Stanford once came across poachers carrying spears and using dogs in Gombe National Park in Tanzania.

"It was an eyeopener that even in a park ... [where] we think we know what's going on, we really don't," he said. "So, you can imagine in larger tracts of forest the kind of stuff that happens every day."

Eco-tourism 'a double-edge sword'

Stanford offers eco-tourism as a potential solution to help save the great apes, but it's one that worries conservationists because it is "a double-edge sword."

It provides an incentive for local people to protect the endangered animal, he said, because "they are worth much more alive than dead" when tourists are flocking to the area and paying to see the species.

However, he said, the "whole system can break down very easily" when the countries lack democracy and political stability. If tourists believe the area is dangerous, they will stop coming and remove the incentive to respect the animals.

There's also the risk of bringing disease into their habitat, he said, by allowing people so close to them and building infrastructure — like safari lodges and trash disposal systems — to support the eco-tourism.

Yet, Stanford remains hopeful that the world won't let the great apes become extinct.

"I would hope … that in the 22nd century we'll have a good balance of having enough protected areas and wild populations," he said, "and have good reasons for local people not to want to get rid of those natural areas anymore."