Aisling Irwin talks to Jane Goodall, the first zoologist to credit chimpanzees with personalities.

The dramatic moment when chimpanzees were first spotted using tools: "Evered, as he climbed through a tree, suddenly stopped and, with his face close to the bark, peered into what looked like a small hollow. He picked a handful of leaves, chewed them for a moment, took them out of his mouth, and pushed them down into the hollow. As he withdrew them we saw the gleam of water. Quickly Evered sucked the liquid from his homemade sponge . . . "

Jane Goodall's discovery that chimpanzees make and use tools distorted the line drawn by humans to separate themselves from other animals. It was the second of a series of dramatic discoveries she made over decades, by watching and watching, deep in the forests of the Gombe chimpanzee reserve in Tanzania. She watched from up in trees, down in bushes and perched on mountain tops overlooking the reserve.

Now she sits in a deckchair, in the sunny gardens of London's Royal Overseas League. A delicate figure with an open face and very dark eyes, at 62 she is growing old gracefully. She is wearing - unusually, one assumes - a smart dress, suitable garb for receiving a CBE. She soon kicks her shoes off, saying they are uncomfortable.

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The CBE, and other accolades such as the National Geographic Society's Hubbard medal, its highest award, mark the admiration with which Goodall is regarded by the establishment. She opened our eyes to the complexity of chimpanzee society, with its variety of personalities, its mass of human-like relationships. Eminent biologist Robert Hinde, master of St John's College, Oxford, says of the woman who is 11 years his junior and whom he once supervised: "She changed the way I worked. She saw the animals as individuals. She taught me that you couldn't add the data on a lot of animals together in a simple way."

But she was not always accepted in academe. When she first came across academic zoology it was full of scientists who, she says, "chopped animals up to see how they worked". This was anathema to a keen and patient observer of primate behaviour who seems always to have had an emotional independence from the world of universities and scientific laboratories. She single-mindedly followed her goal of studying chimpanzees, a route which sometimes converged with traditional academia but often did not.

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It did not converge at the start, when she left her Bournemouth home, with an A level in biology and a dream she had had since eight, inspired by Dr Doolittle, of living in Africa and writing about wild animals. She had saved for a holiday in Tanzania. There she found a job as assistant secretary for Louis Leakey, the famous palaeontologist, who was curator at the National Museum of natural history in Nairobi and who became her mentor.

Why did Leakey choose this woman, in her mid-twenties, with no degree (she couldn't afford it), to fulfil his amibitious plan of sending someone to observe the wild chimpanzees on the shores of Lake Tanganyika? Because, as well as being a keen observer, she was simple in habits, patient, degree-less, independent of mind, and female. "He realised that I didn't care about clothes, hairdressing and parties," she says, perched on the edge of her deckchair. Her simple way of living, which included eating only once a day, was essential for studying chimpanzees. (The simplicity persists - she celebrated her CBE, of which she is proud, with a sandwich.) Goodall jumped at Leakey's idea and soon she, and her amazingly supportive mother, were living in a tent by the lake. She would leave at dawn with nothing but a kettle for coffee to sustain her through the day.

Leakey's choice of a patient and persistent researcher was wise. It took six months before she was able to get nearer than 500 yards to any chimpanzee. And a sense of persistence exudes from her descriptions: "For three hours I watched the chimps feeding"; "I was not only weary but soaking wet from crawling through dense undergrowth".

Her first six months of frustration were rewarded with two discoveries which excited Leakey, and via him, the wider world. She demolished the idea that chimpanzees were primarily vegetarians with her discovery of chimps eating baby pigs and baby baboons. Later, she would see them hunt. Then, after "a frustrating morning, tramping up and down three valleys with never a sign or sound of a chimpanzee", she saw the chimp she was to love most, David Graybeard, using a grass stem to poke into a termite mound and withdraw insects to eat. Not only did she see chimps using tools but making them as well, by stripping down twigs.

At the time the study of animals was full of taboos: animals were not credited with having emotions, minds, personalities. Without a degree, Goodall had not learned about the sin of anthropomorphism: shockingly, she gave the chimps names; she recorded anecdotes as if they might be scientifically useful; when chimps appeared to be jealous, happy or afraid, she recorded that they were jealous, happy or afraid.

Hinde says that it was vital for Goodall's keen observations to be moulded by scientific discipline. This she acquired when she started her PhD at Cambridge at 28. Exceptionally, Cambridge allowed her in without a first degree because of the work she had done. But she was very different from the other students. She was older; she had been in the field; her direct knowledge enabled her to contradict many of their beliefs. Above all she hated their assumptions and their methods. "They couldn't accept how like us chimps were."

But it was her independence of mind which really enabled Goodall to wreak such a change in the way many academic disciplines consider primates. She did not, for example, give in to Nature when she received the proofs of her first paper for that journal, in 1964. The editors had replaced the words "he", "her" and "who" with "it" and "which": she scrawled them out and reinstated their anthropomorphic alternatives. Nature demurred.

In fact, Goodall could not avoid using unacceptable words such as "adolescence", "childhood", "social excitement" to describe the complexity of what she saw. She watched, for example, the mother-infant relationship. Mothers often form the head of a family group of females and infants who will stick together and support each other throughout their lives. Chimps remain dependent on their mothers for years: even at three years old they may die if their mothers disappear. It would appear that they can die of depression since, by three, they should be physically able to cope alone. Some chimps adopt their orphaned infant siblings. Goodall wrote: "Who would have guessed that at five years of age a child might still be suckling and sleeping with his mother at night? Who would have dreamed that a socially mature male of about 18 years of age would still spend much time in the company of his old mother?"

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But her sex led to problems while she was at Cambridge. It was during the period when the National Geographic magazine put her on its cover. "It was a picture of me in shorts with my chimps," says Goodall, sure that she would not have been a "cover girl" if she had been a man. Cambridge wanted her to wait until she had her PhD before the exposure. But she wanted to please the National Geographic Society, which had faithfully been funding her work.

The National Geographic Society had also funded a photographer to document the chimpanzees: Hugo van Lawick arrived and the two fell in love. They married in 1964. The wedding cake carried a clay model of David Graybeard. They had one son, in 1967, and again Goodall broke the rules, this time with his early upbringing.

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Goodall believes that there is little difference between chimpanzee and human infants before they reach the stage of talking. Over the years she had observed that the most socially successful chimps were the ones whose mothers paid them lots of attention when they were young: plenty of touching; keeping the infant constantly nearby; suckling on request and toleration of misbehaviour when the infant is too young to grasp the difference between right and wrong. So Goodall gave the young Hugo absolute security, diverting him rather than punishing him when he misbehaved and exposing him to two or three trustworthy adults. "Everybody said he would never be able to go out in the world if I treated him like that," she says. "In fact he is now supremely self-confident." She likes to attribute this to his early experience, in which case it must also have helped him through an early start in prep school away from home and his parents' divorce in the early 1970s.

If Goodall had stopped her work after the first ten years she would never have witnessed the four-year reign of terror by Passion and her daughter, Pom. They stalked the mothers in the community, killing and eating their new infants. Similarly, she would never have witnessed a four-year war, in which one chimpanzee community systematically exterminated another.

Until this infanticide, the only cannibalism Goodall had witnessed was the result of an attack by a group of males, while they were protecting their territory, on an alien female. During this attack the stranger's baby, possibly accidentally, was killed. The males ate a small bit of the baby.

"In contrast," wrote Goodall, "Passion's attack on Gilka seemed to have been directed to one end only - the capture of her baby. And the carcass was consumed in the way that normal prey is consumed, slowly and with relish."

Gilka lost three babies to Passion, who would kill them by biting them in the neck, and then had no more. Passion stopped when she had her own baby.

"Those events changed for ever my view of chimpanzee nature," Goodall wrote in her second book, Through a Window. "For so many years I had believed that chimpanzees, while showing uncanny similarities to humans in many ways were, by and large, 'nicer' than us. Suddenly I found that under certain circumstances they could be just as brutal.

"Often when I woke in the night, horrific pictures sprang unbidden to my mind - Satan, cupping his hand below Sniff's chin to drink the blood that welled from a great wound on his face; old Rudolf, usually so benign, standing upright to hurl a four-pound rock at Godi's prostrate body; Jomeo tearing a strip of skin from De's thigh".

Goodall's understanding of chimpanzees has made it inevitable that she should tackle their abuse by humans. They languish as tourist attractions on beaches; they suffer grotesquely as pets; they have miserable lives when kept for scientific experimentation. Goodall has built up a reputation as an animal welfare campaigner and the welfarists she works with seem to worship her. She says her lecturing work is a mission: "It's as though someone takes over when I speak. I can almost stand aside".

She argues that if chimpanzees are to be used to study human illnesses then they should be treated as "honoured guests in the lab" - given space, things to do, the comfort of physical contact with other chimps and a comfortable retirement.

Despite her horror of the conditions in laboratories she visits, she is controlled in her reaction to those scientists who allow such conditions to persist. "Most people are not evil," she explains, with a calm look on her clear face. "People mostly do bad things because they haven't understood or haven't bothered to think through what they are doing. It's when people begin to understand in their own hearts that they will do something".

Goodall believes in gradual change and compromise. As a result, she has alienated some animal rights groups, including the World Society for the Protection of Animals, which has run high profile campaigns to seize dancing bears and maltreated apes. She resigned as an adviser to the charity earlier this year, arguing that aggressive campaigns alienate established activists and governments.

Back at Gombe there is a flourishing research centre, where she now spends only five weeks a year. She says: "I miss it but I have it inside me so that just ten minutes in the forest fills me up."

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