By Caroline Ryan
BBC News health reporter, Prague
More should be done to help women in their 30s and 40s become mothers, a fertility expert has said.
Patricia Rashbrook is to become a mother at 63
Dr Laurence Shaw, of the Bridge Centre, London will tell a European fertility conference in Prague increased lifespans mean more childbearing time.
He will say declining fertility evolved so that women in tribes could forage instead of being occupied by childcare.
But now this is no longer a problem, society should use technology to help older women conceive, Dr Shaw believes.
Many anthropologists believe women's fertility decreases, to the point of the menopause, because women historically needed to be available to forage for food for the good of the group.
Studies suggest women with small babies focussed on providing food for them.
Declining fertility is a natural contraceptive which means women are less likely to have children and therefore be distracted from foraging.
Dr Shaw says: "Homo sapiens have existed for 150,000 years and for all of that time until about 100 to 150 years ago, women had their babies when they were in their late teens and early twenties when their fertility was at its peak.
"Before we criticise 62-year-old women who want to have babies, we should remember that it was not so long ago that women would only have had about 20 or 30 years to care for their offspring and help with the next generation.
"Nowadays 60-year old women in many industrialised countries, have a life expectancy of 80 or 90, so there is no difference in terms of the length of their survival after the birth of a baby than there would have been for most of human existence."
He stopped short of calling for IVF treatment for women in their 60s, but said society should do more to help those women wanting to start families later in life.
"We should use technology to help further with finding better and safer hormone replacement therapies, and with fertility treatments for those seeking pregnancy in their 30s and 40s.
"We need to look at things not just in terms of the 21st century, but in the overall context of evolutionary progress."
Dr Allan Pacey, Senior Lecturer at the University of Sheffield and Honorary Secretary of the British Fertility Society, said: "Long post-menopausal lifespans are almost entirely a human trait and there are many theories to explain why women go through the menopause in contrast to most other animal species.
"One is that they can enhance their own daughters' fertility by becoming helpful grandparents and this is better than having further children themselves."
He added: "In today's modern society the evolutionary pressures that led to this are clearly not the same as they were when we were hunter-gatherers.
"But I am not sure this makes giving IVF to older post-menopausal women any more acceptable."
He said the availability of donor eggs and the right medical management meant post-menopausal women could get pregnant, there were clear risks involved in maintaining that pregnancy.
Dr Pacey added: "Most professionals agree that treatment using donor eggs should generally be confined to women under the age of 50."