So much of what babies do - and how their parents react - is a relic of our hunter-gatherer past, says Desmond Morris in his new book, writes Mary Russell

HE HAS PUBLISHED some 50 books, enjoys a parallel career as a surrealist painter, does one drawing every day without fail, has a theory about the office of the future (it will be a huge televisual voice-activated screen occupying one whole wall of your living room, on which your work colleagues will appear in hologram form), and because he is entranced with the subject matter, is unashamedly enthusiastic about his latest book, called simply Baby. Yes, Desmond Morris is back again with an examination of that most intriguing of animals, the human infant.

It is 41 years since he first hit the headlines with The Naked Ape. "If I wrote that book now," Morris tells me in his Oxford home, "I'd call it 'The Talking Ape', because that's what sets us apart from other animals: we can make symbolic equations. I might say to you, 'look at that tree', and the sound of the word bears no relation to a tree, yet you immediately visualise a tree. I know we're only divided from apes by two chromosomes, but they're pretty big chromosomes."

An instant bestseller (12 million copies sold to date) it allowed him and his wife, Ramona, to buy a house in Malta, where she had their son, Jason.

"We were married for 16 years," he says, "and people were asking why we didn't have a child. They thought I should be studying a human child rather than other animals, but we were living in a flat in London and an urban environment with all that concrete is no place to raise a child. Then, when he was born, people said 'now you can study him', but I said, 'no, I'm going to love him'. You can get too scientific."

Jason, now himself the father of four children, lives with his wife in Co Kildare, where he is director of racing at Horse Racing Ireland.

This latest book, Baby, is gorgeously illustrated, with the text covering every aspect of human growth from conception through to the second year, thus taking in that minefield of childhood: the terrible twos. Not that Morris sees it like that at all: "What happens is that a small baby who is secure and loved can do very little for the first year or so, but then that very security allows him to try things out and sometimes it gets out of hand."

Thus the terrible twos go through what he benignly describes as the "eccentric phase". Does he tell us how to deal with such matters? "No. I just give people the facts about the child's development, and after that it's up to them," he says.

HE HAS GREAT sympathy for the young single parent - it's usually a mother - coping on her own in an urban setting. "That's a very lonely place to be. It's part of our birthright to come together in groups and that doesn't happen any more," he says.

And then he gets to it - the hunter-gatherer bit - about how in the old days, and we're really going back here, the male could display his manliness by hunting and killing and so forth, and thus, his masculinity recognised and established, he could return home to display tenderness towards his children without anyone calling him a girl's blouse. The other thing was that when we lived in small tribes, the mother could take her child with her to work, swaddled on her back or placed in a hanging basket on a tree so that the two were always within sight or hearing of each other. "Now," Morris says, "that's gone. You can't breastfeed in the boardroom - unless you're Karren Brady ."

His other concern is with what he calls "yes parents" and "no parents". A controlling one (a no parent) robs the child of the feeling that the world is full of possibilities. These children grow up to be over-cautious and conservative in their outlook, whereas a child with a yes parent is adventurous and non-conformist. I can tell from this that his own mother was a yes mother and he agrees.

"When I was about five or six, I asked if I could have a tame fox for a pet, and I got not one but two."

And lots of other creatures as well, which was very noble of his mother, he remarks, because we all know it's the mother who ends up looking after all these pets.

Mothers rate big with Morris and this is partly because the female is pre-programmed to relate to babies. Come, I can't help interrupting, surely nurture is a big player in the ping-pong game of gender bias. But he is unperturbed.

"I'm not so sure," he says, far too genial to contradict me outright. "Children will make a choice. They'll filter things."

And so I tell him of my son who, when small, was given a doll's house to play with and the doll family always ended up on the roof of the house awaiting rescue by a fire engine or a helicopter because some action-packed drama was taking place below. He nods. "Yes, the child will make a choice that accords with its gender," he says.

But I'm still not convinced by his pre-programming theory. How can he say for sure, I ask, feeling like Doubting Thomas. After all, this is a man who has spent his life studying animal behaviour.

"Well, there's the pupil test," he explains. "You have a device that measures pupil dilation, which, as we all know, is an indication of how much you like something. When you show a female an image of a baby, her pupils will dilate whether or not she has had a baby. But do the same with a male who is not yet a father and there is no response. No emotional bonding. However, do it with a male who has become a father and the pupils dilate just like a female's."

SITTING IN MORRIS'S wonderfully comfortable library, its walls lined with books (all catalogued), masks and whatnot on the wall, rugs on the floor and a soft, low sofa that just begs to be sat upon - it's a joy to watch the show as he acts out a woman's pupils dilat- ing to an alarming size, popping his own eyes to emphasise his point. And because, in this dark world of bank crashes and credit crunches, he's so smilingly positive, you'd almost want to hug him. But of course I don't, because this is a serious interview, and so instead I ask him which creature might act as the best role model for a would-be parent.

"Birds," he says promptly. "They have to make a nest and keep the egg warm, and both parents feed the young, and that's what's important: pair bonding. It demonstrates that human babies need two parents just as birds do. This is partly due to the fact that humans have serial litters. They need someone else there. In the animal world generally, a cat or a bitch will have a litter but won't have another one till those babies have grown up and left the nest. The human mother will have a second litter before the first one is even weaned, sometimes."

It's not like monkeys, which cling to their mother's fur and go wherever she goes. Incidentally, in the human baby, there's what's called the Moro reflex. Check it out. It occurs in very young babies when they fling their arms out and then bring them together again as if embracing something. They do the same with their legs.

"It's a relic gesture," says Morris's book, "from when a baby felt itself falling from its mother's body."

Although Morris doesn't tell parents how to behave, he does hint: "The relic gesture alerts the mother to the fact that her baby is suddenly feeling unsafe and physically insecure."

So do something about it, is the gentle hint.

The baby book, says Morris, was a gift, as it allowed him to do what he'd trained as a zoologist to do: observe. "I'm not an experimenter. I just watch. You can't ask babies questions or give them a questionnaire to fill in. You just watch them."

There are gender differences that he outlines but doesn't emphasise. Boy babies cry less because in the hunter-gatherer period they couldn't make much noise or their prey would run away. Men are focused on one goal while women multi-task, though that doesn't mean one can't do the other.

" Ramona," he says, "can multi-task, but so can I. It just means I have to try a little harder."

The book is full of observations that we once knew but have forgotten. Small children's feet are best left unshod, so only put shoes on them when they go outside. Tests have shown that toddlers rarely stray more than 60 metres from their mothers, so you don't have to yank them back, they'll come of their own accord. Unless they're going through their eccentric phase, of course. At which point, you may find you're giving yourself a hug. This, as Morris notes in his book, People Watching, is a comforting device employed by adults in moments of stress. Well, it's better than reaching for a bottle of mother's ruin.

• Baby: The Amazing Story of the First Two Years of Life, by Desmond Morris, is published by Hamlyn, £25