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Sunday, Aug. 12, 2012

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Hello kiddy: Japan's fertility rate has dropped to fewer than two children per woman, which will result in a significantly lower and older population. New advances in science, however, could make it possible to grow a baby in an artificial womb, outside of the human body. AP

NATURAL SELECTIONS

Excuse this proud new father — it's time to indulge in some baby talk


I'll preface this column by admitting that it is fairly common, among journalists on the science and health beats, that after they personally reproduce they experience a burning desire to write about the science of childbirth. Seasoned editors know to expect that postnatal reporters will start pitching stories on the psychology of the newborn child, on fetal brain development and on hormonal and genetic influences on natal behavior.

My excuse for doing the same — having recently passed that milestone in adult life and become a father — is simple: It's cool, and I've been writing about this stuff for ages anyway, even before I was a dad. In any case, as everyone knows, having children is something that people in ever-graying Japan need to do more of, so we could do with more stories on it. And, as they say in Hollywood, this time it's personal.

In this column, then, we'll look at whether it could be possible to beat the biological clock.

To recap the situation in Japan: In the next 50 years, if the birth rate stays as it is now, Japan's population will shrink by a third. There are currently 127.55 million people in Japan; by 2060 there will be 86.7 million. The fertility rate — the number of children had by each woman — is currently around 1.35, but for a population just to be sustained that number needs to be over 2.

At the same time, life expectancy will continue to increase. This is why Japan is said to have a graying population. The problem — which has serious economic as well as social implications as the workforce declines — is something that occupies much of Teruo Fujii's time. The University of Tokyo professor is one of Japan's leading authorities in ectogenesis: the growth of a baby in an artificial womb, outside of the human body.

There's a long way to go before that technology — famously explored in Aldous Huxley's dystopian-future novel "Brave New World" — is up and running. But Fujii's team is taking some of the first steps.

A few years ago they developed a micro-scale device that held living cells taken from the lining of the womb, and which provided a venue for human eggs to be fertilized. It was similar to how embryos are currently made using in vitro fertilization, but it mimicked more closely the conditions of the human body. Fuji's experiments using mouse embryos suggested it works better than conventional IVF.

Now there's more research that could boost the chances of IVF and that might even have ramifications for Japan's aging population.

We've all heard of the notion of the biological clock — the idea that fertility declines as you get older. One of the main drivers of the clock is the fact that number of eggs in a woman's body declines throughout her life. A baby girl is born with 1-2 million eggs, but the clock has already been ticking from when she was in the womb: At 16-20 weeks a fetus has 6-7 million eggs.

By the time the girl reaches puberty, she has some 300,000 eggs. Most have degenerated, and the speed of degeneration increases as a woman approaches menopause. That stage marks the end of a woman's fertility: All her eggs are gone by that point.

It has long been thought that a woman is born with all the eggs she will ever have, and that no more are made during her life. However, a new genetic study suggests that extra eggs may in fact be formed during adult life.

Ehud Shapiro, of the Weizmann Institute of Science in Israel, and colleagues used a genetic technique that allowed them to examine the behavior of special cells in the ovaries of mice that generate the cells that develop into oocytes — eggs. Their work, published in the journal PLOS Genetics (DOI: 10.1371/journal.pgen.1002477), suggests that these "progenitor cells" divide during adult life, and not just while in the womb as had been thought. This means that new eggs are probably being made.

Most such work is done in mice, so there's always the caveat that it might not reflect what happens in humans. However, the researchers say there is good evidence that a similar production of new eggs occurs in women.

There are currently at least two ways that women attempt to prolong their childbearing years: one is to freeze some of their eggs; the other to freeze an entire ovary. Both options are already being used in various clinics in the United States and in Britain, often at great expense to the woman. They are both controversial, as the evidence that frozen eggs or ovaries can be thawed and used years later to produce viable offspring is equivocal. Children have certainly been born using frozen eggs, but there are questions over the efficiency of the technique and the American Society for Reproductive Medicine has not (yet) given its backing.

It's early days, but Shapiro's work suggests that perhaps these progenitor cells could be targeted and even encouraged to develop in older women with declining fertility. As usual, more research is needed. I'll report on any advances here.

Rowan Hooper (@rowhoop on Twitter) is the News Editor of New Scientist magazine. The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is "Hito wa Ima mo Shinka Shiteru (The Evolving Human)."


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