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How long should we let human embryos grow in the lab? Until now that question was largely academic. Going beyond 7 days in vitro was very rare, with 9 days the longest achieved.

Now two new milestone studies have managed to keep embryos growing for 12 to 13 days before destroying them. This means it might now be technically possible to grow human embryos for a day or two past the 14-day limit adopted by many countries.

At a press conference in London, at the University of Cambridge, who led one of the studies, said that much of value might be learned by studying embryos past 14 days. 鈥淟onger culture could provide absolutely critical information,鈥� she said.

But she stressed that this is a matter for society at large, and that she is not calling for the limit to be extended. 鈥淚 have no view on that right now,鈥� she told 快猫短视频.

Even if researchers are not yet calling for an extension, the latest work will inevitably raise heated arguments about personhood and the sanctity of life 鈥� all of which will distract us from any serious discussion of how embryo research might provide a better understanding of the biological realities of developing life.

Primitive streak

How did we get here? In 1984, the UK鈥檚 reinforced the idea of a 14-day limit by pointing to the appearance of an alignment of cells around that time known as the primitive streak. It described it as the start of embryonic organisation that will eventually lead to the nervous system.

At the time, 快猫短视频 noted that this could be seen as using . It is also the point beyond which twinning is no longer possible, so some argue that this marks the beginning of an individual person.

Definitions of 鈥減ersonhood鈥� are socially negotiated. Facts about development are not. The identification of 14 days as crucial was socially constructed and is not biologically definitive. Embryos develop at different rates, depending on temperature and other factors. One embryo might be much further developed at 14 days than another. So, whether we look at 12, 13, 14, or more days doesn鈥檛 matter. The question is: what is the embryo at that point?

In the glass dish, an embryo is largely undifferentiated, has no neural structure, and is not viable. Unless and until implanted, it cannot live on its own.

Therefore, the critical point is that an embryo in a dish is a bunch of cells in a dish. Then, when implanted, it is a growing and differentiating collection of cells in a uterus and it becomes increasingly connected with and dependent upon that uterus for the exchange of nutrients and waste products. Implantation is vital, mothers are vital.

Only gradually, at about 8 weeks, does the embryo become a fetus with the essential organs at least roughly mapped out. Only much later is the nervous system developed, and only much, much later does the fetus have the capacity to feel pain.

A primitive streak is not a nervous system. A bunch of cells is not an organised human being in any robust biological sense. A number of days does not define life.

Additional reporting by Michael Le Page at 快猫短视频