An animal that could hold the key to life-threatening human diseases is on the, researchers say. Nearly all of the world's lemurs reside in Madagascar, an island nation off the southeast coast of Africa.
We hiked up steep hills for six hours to find them hidden deep in the Ranomafana National Park. There are over 100 different species, including ring-tailed lemurs, which are playful and smart. We spot a rare Sifaka lemur — one of only about 2,000 left in the world.
Lemurs share many of the same genes as humans. They're not as close as chimpanzees but they're still family. The mouse lemur, for example, is our smallest cousin.
"They get some of the same diseases that we get. They can come down with Alzheimer's, diabetes, they can develop obesity," said anthropologist Dr. Patricia Wright of Stony Brook University in New York.
"A lot of the experiments on human health are done on the mouse and the mouse is not related to us and it only lives two years so you couldn't possibly study some of the long-term kind of diseases," said Wright, who has studied lemurs for more than 30 years.
Wright has turned this rainforest to a laboratory in the wild. Her team has embedded computer chips in hundreds of lemurs so she can monitor the development of Alzheimer's for an average of 20 years. She's built a genetic data bank from her research and her hope is that it will lead to new drugs one day.
It's now a race against time. Lemurs cannot survive without forests and 95 percent of the lemurs' natural habitat outside this park is gone, the land burned and cleared for crops.
"It's like burning a library," Wright told CBS News foreign correspondent Debora Patta in a report for "Down to Earth" by CBS News on Facebook Watch. "It's a real shame, but hopefully we'll be able to save these little guys and we'll be unlock their secrets."
One day we went along with Wright's researchers. They baited traps and tied them to branches to lure the tiny lemur inside. When we returned to check them that night, the noise of the rain forest surrounded us, throbbing and pulsing in the dark. They had trapped six lemurs out of 70 traps laid.
Back at the camp, researchers work under a red light to mimic the night-time conditions mouse lemurs like best and to prevent damage to their eyes. Testing the lemurs' strength — think of a Fitbit for lemurs — was also a test of patience.
Each one is weighed and measured. Researchers are looking for early signs of disease or weight loss. Once the tests are over, they are released unharmed back into the wild.
Now the lemurs are facing a new threat. Madagascar has been hard hit by. In recent years, the island has been battered by unusually strong cyclones, severe drought and then torrential rain.
"It's a much more turbulent time. The rainy season doesn't come at the right time. The dry season is more extended," Wright said. "Everything is out of balance."
The fruit trees, the lemurs' main food source, did not flower this year.
"This never happened before. For the lemurs, its devastating because it means they can't get fat enough to produce offspring," Wright explained. "They probably won't starve but they certainly are going to go hungry."
The number of baby lemurs that survive beyond six months has dropped to 47 percent from 70 percent in just three years.
Wright told us she was shocked by other changes she saw on this trip, too.
"This use to be a lake and now its all dried up and its been a lake that's been shrinking every year. This time, there's no water at all. There use to be crocodiles here last year," she said. "It's shocking."
Wright is fearful the devastating changes occurring on the island could mean the end of her lemurs. She's frustrated by how slow some are recognize the danger.
"Madagascar itself is like a canary in the coal mine. This island is very vulnerable and somakes a bigger impact here," said Wright. "It's a warning signal to the world."