According to Jane Goodall, old female chimpanzees “continue to have a baby every five years. ... It’s the tragedy of having no menopause.” (BERTRAND GUAY/AFP/GETTY IMAGES)

Jane Goodall, 77, has been studying chimpanzees for most of her life. Encouraged by famed anthropologist Louis Leakey and only 26 years old, Goodall set up camp in Gombe National Park in Tanzania to observe a group of wild chimps up close. She is credited with discovering that chimps use tools, are not vegetarians, care for one another and sometimes use violence against other chimps. She has also used her years of research — and hers is one of the longest scientific research projects in the world — to show how closely related humans and chimps are.

Now, in what she calls the final era of her life, Goodall is focusing less on the chimps and more on their human relatives — young ones in particular — encouraging them with her “Roots & Shoots” campaign to become good stewards of the environment. Recently Goodall spoke with The Post about the process of aging, from both a chimp’s perspective and from her uniquely human one.

You’ve spent your life studying chimps. Can you describe their aging process?

What you notice, wherever, in the wild or captivity, is teeth getting worn down, the body getting shrunken, losing its gloss; instead of being glossy black, it becomes brown gray. Their eyes become sunken. Their movement gets slower. They tend to get more solitary. They tend to move away from excited groups.

Here is where you notice a huge difference in an old male and an old female. Old females have no real menopause. They continue to have a baby every five years. Even when she is very old, she has her youngish child. It’s the tragedy of having no menopause. The last child is likely to die because the mother is too old to provide proper nutrition.

What about an old male chimpanzee?

Most of the chimps in the wild don’t live to be that old. An old male can be very lonely. Some old males make very close bonds. Very often you get a couple of old guys hanging out and grooming each other.

Who is mating with old females?

Everybody. You’re more beloved by the males. You’re not scared. You know all the tricks. You are very popular. You quite like it. But remember, we don’t see very old females. Most wild chimps don’t live more than 50 years.

In captivity, the oldest one is right near the age where I am now. She’s at least 74. She’s called Little Mama. There are two really old females in the wild. Old Flo, who was definitely over 50 when she died. She had a sort of menopause. She got so frail. Her last child died. She was accompanied all the time by her 8-year-old son. She was never alone.

The other one is a female called Sprout. And the most lovely story about Sprout is when her fully adult, magnificent son, Satan, was 23 years old, he threatened a young male because he wanted to take over the fruit bunch on a tree. So the young male moved away and screamed. The young male’s older brother heard his brother scream, swung from a tree and both of them attacked Satan. And bounding through the branches came this ancient female, all shrunken, weighing half of the three males, dropped onto the three fighting males and with her tiny, little frail hands, starting hitting away at the brothers and chased them away. That was Satan’s old mother.

So have the chimps taught you about the aging process?

Not really. I don’t think I’ve learned what I know about aging from the chimps.

How old do you feel?

I don’t feel any particular age. Seventy-eight sounds old. I don’t feel old. My mind has not gotten cloudy.

Do you have aches and pains?

The first thing you notice is it’s not so easy to get up from the floor.

My sister and I were complaining the other day and I remember my mother — all my family lived to be over 90 — watching her getting up from the floor, having to push herself up on a chair. I am thinking, “Oh, dear,” and gradually it creeps up on you that you can’t leap up off the floor.

But I still leap up in funny places. Last night we were off to somebody’s house for an event, a dinner, and someone brought their dog. There wasn’t enough room in the car, and the dog didn’t want to get in the back. I climbed in the back. I don’t feel 78.

Who is in better shape, you or your sister?

I’m in better shape. She is four years younger. She had a bad time with her knee, and she should have it fixed. Otherwise she is in perfectly good health. She never gets sick. We have good genes on both sides, mother and father. That is just luck.

Do you still travel 300 days a year? Isn’t that physically exhausting?

I travel more now. I could not have done it when I was 30. I would get sick. I carried on with a tour, but I’d get sick. On one occasion I had a fever; I didn’t know at it that time. I went to the doctor and he said, “You have these antibodies; when did you have mononucleosis?” I said I didn’t know I had it. He said, “That is why you are feeling so absolutely deadly.” A couple of times I had to stop in the middle of a lecture. I was about to faint. That was in my 30s and 40s. Now I am nearly 80.

I think it is very encouraging to people who are actually 80 and think they are too old to do anything to know you can be stronger at 78 than when you were at 30 or 40. I am more determined, and there’s shorter time for me on Earth, I know that.

How do you keep yourself so vital?

There is so much I know I have to do! And fortunately I get back to Gombe twice a year. I always insist that for one of the precious four days [I have in Gombe] I be left completely alone so I can recharge. It’s my spiritual energy. When I’m in England, which is home, where I grew up, where my sister and her family live, there are always dogs. There I get my relaxation walking the dogs where I used to scramble as a child.

Do you keep up with technology?

I definitely do e-mails. I take my laptop. I do my writing on it. I will not have a BlackBerry.

I have a cellphone, but I don’t know the number. I use it simply to call somebody if I need to. The cellphone is never on. The cellphone is not part of my life. Someone does a blog for me. I don’t tweet and twitter. When people ask me to join their Facebook, I delete it.

Where technology is really, really useful is that we have been able to do high-resolution maps all around Gombe. We have a GPS. And we now have these Android cellphones — whatever they are, I don’t pretend to understand — which are used by forest monitors who are helping to protect and restore the forest and their village.

What are you still hoping to do?

Growing what is already there. Roots and Shoots [an environmental program for young people run by the Jane Goodall Institute] is in 100 countries.

I am encouraging people to think about the consequences of the choices they make: What did you buy? Where did it come from? What’s it made of? Does it come from very far away? Was it involved in child slave labor in India or China? Did it involve horrible cruelty to animals, like all of the meat we buy from farm animals? They face torture.

I try to make use of my own ecological perspective. Did I turn lights off? Did I turn off my computer? All of these seemingly little things, when millions of people do them, that starts a mountain of change.

My great hope is in young people, and at the same time I feel it is terribly important to talk with decision-makers.

I just talked to AARP. Those people are incredibly influential, and they are at the stage of their life [that] they can start thinking about the contribution they’ve made to the planet, especially if they have grandchildren. It may inspire things like “I did some terrible things, and now I have time to make up for it.”

I really try to walk the talk, although my stupid lifestyle involves a lot of travel and CO2. My travel is not in a private jet. I plant hundreds of thousands of trees.

How long have you been a vegetarian?

Since about the late ’50s. I read Peter Singer’s book about animal liberation. After reading that book, my next meal came along, and I saw meat on the plate. I looked down and said this symbolizes fear, pain and death, and I don’t want that in my body. I stopped just like that, boom.

I do a lot of things boom.