"Science is a battleground when it comes to women's minds and bodies."

That's science journalist and author Angela Saini, who has been looking into one of the fastest growing fields of research: sex difference.

She believes science is susceptible to gender bias, as well as politics and cultural context.

"That can influence the outcome of research as much as anything else," she told an audience at the recent Sydney Writers' Festival.

There, Saini outlined which theories about women she believes should be put back under the microscope.

Sex difference

Female sexual behaviour is far more complicated than we think, and Saini said many commonly accepted theories don't take that into account.

"Understanding female sexuality really gets to the heart of this question of sex difference," she said.

Think of 1970s sexual selection science, she said, and the theory of "parental investment".

It argues that as women have a finite number of eggs, and invest a huge amount of energy carrying a child and lactating to sustain it, it's in their interest to be monogamous.

"On the other hand," said Saini, explaining the theory, "men have loads of sperm and very little parental investment so it's in their interest to be as promiscuous as possible".

"This explains human sexual behaviour and... all the sex differences that we see between us."

Science journalist and author Angela Saini speaking at the recent Sydney Writers' Festival.

She said the idea that men are denying their natural state by being monogamous highlights a moral double standard: promiscuity is frowned upon in women but accepted in men.

But a growing body of research is expanding on accepted ideas about female sexual behaviour.

For example, Saini said, anthropologists have observed that the Himba people in Namibia have a different moral code surrounding marriage.

It means both men and women are free to have affairs, "and they do, very happily".

Scientists are also looking to other species to observe sexuality.

The female blue tit mates with multiple male partners. ( Unsplash.com: dfkt, CC-0 )

They have learned, for example, that so-called monogamous animals such as some birds "are actually going out and having affairs with other birds".

"There's no reason why we should have to have these rules and not another set of rules," Saini said.

"The codes that we have drawn up for ourselves are really just handmade."

The motherhood myth

Saini also challenged ideals regarding motherhood and parenthood.

"We demand perfection of women," she said.

"You've had this baby, now you are Mary, now you have to fulfil this role, when, actually, that's not how things have ever been or how they are now."

She said parenting practices dating back over a million years present a more egalitarian model.

"If you want to imagine who we were for the bulk of human history, hunter gatherers are a window on that," she said.

They lived in communal societies where the responsibility of caring for children was shared by community members.

Because everyone took a role in parenting, women were able to work — and they always did.

"To have a woman on her own with a child every single day and expecting that to be some kind of natural state because she is a mother — that is not how we have ever lived," Saini said.

Hunter gatherers were more egalitarian in parenting than in modern Western societies, Saini said. ( Getty: Mauricio Anton )

The notion that women have a biologically determined drive to bear children is also common, with some science even arguing that maternal love is written into a woman's brain.

Anthropological analysis indicates otherwise, Saini said.

"We forget just how common it is for women to neglect their children, in history to kill their children, behave very badly towards their children," she said.

Research suggests both mothers and father may physically abuse children and in some age groups the mother is more likely to be the perpetrator. It has also found mental illnesses such as psychosis are a contributing factor to the incidence of parents harming a child.

But Saini said the occurrence of harm undermines ideas of mothering being biologically innate.

"If motherhood was some kind of natural thing that every woman was endowed with by biology, then how could that happen?" she asked.

"The answer is that the reality of motherhood throughout history has been a strategic one.

"If she can't cope, if she doesn't have the support she needs, a woman is more likely to neglect and kill her child.

"That's a fact. And we see it in other species too. The runt of the litter might get killed off if the mother knows she can't look after it."

Menopause and the grandmother theory

Evolution usually dictates that infertility is the end of the line, and Saini said it is a mystery why women live such long, healthy lives beyond their fertile years.

"By the hard, very tough rules of nature, that shouldn't happen," she said.

No other primate and only few other species, such as the killer whale, experience menopause at the end of their reproductive years.

That's because, Saini said, "they die around the time they become infertile".

A recent study from McMaster University in Canada argued that the evolutionary reason for women's menopause is men.

It argued that "throughout our history, on average, older men have not found older women attractive, and so they don't need to be fertile," Saini said.

Over time, the lack of reproduction among older women gave rise to menopause as an unintended outcome of natural selection, the research said.

But Saini is not convinced. She said the research is an extension of the 'patriarch hypothesis', "which almost exclusively men have worked on".

In contrast, she said, many women researchers have worked on the 'grandmother hypothesis'.

While it doesn't explain why women experience menopause, it does address the question of why women live so far past their fertility.

According to the theory, grandmothers are crucial to the survival of their families.

"The presence of a grandmother makes it more likely that her children and grandchildren will survive, and we see this statistically," Saini said.

She recounted a story about a nomadic tribeswoman in the Kalahari whose daughter and grandchild were sick and couldn't walk to find new food.

"The grandmother, an elderly woman, picked up her daughter on her shoulders, carried her on her back, and she carried the baby in her arms, and she walked hundreds of miles to catch up to the tribe," Saini said.

"She literally guaranteed the survival of her descendants by that one act."

Many anthropologists have now done research in this area, she said, but observations closer to home can also support the grandmother theory.

"Think of your own lives — the roles that your grandmothers have played in your lives or your children's lives and you can see it play out in action," she said.

The secret to longevity

All over the world women live longer than men — in Australia it's a difference of four years.

Even in infancy there's a mortality difference between the sexes.

Sick or premature babies are more likely survive when they are girls. ( Getty: Westend61 )

"On a ward where you have premature or sick babies, the girls are more likely to survive than the boys," Saini said.

"And that survival edge stays with women their entire lives."

But we don't know why, as the issue hasn't been investigated very much.

We do know women have stronger, more flexible immune systems, and so recover from small illnesses like coughs and colds more quickly.

They might be more robust faced with significant illnesses, too.

"There's a theory now that when you look at all the major causes of death, women seem to survive them when they kill men," Saini said.

"A side effect of this is women live with pain more, so one of the things that doctors say is that men die quicker but women are sicker."

Only now are researchers really looking into the reasons for this, she said, to learn if women's genes or bodies can provide a key to longevity or clues to understanding what makes women so strong.

Going forward, she had one piece of advice above all others: "Read science critically."

"Science gets stuff wrong. That's how science works. You get things wrong and you learn and you do it again," she said.

"We need an honest portrayal of science as an endeavour... on the way mistakes will be made. If we have that honest relationship I think we'll all be better off."