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Podcast Review: The Primitive Streak

24 October 2016
Appeared in BioNews 874

The Primitive Streak

Radiolab, Friday 23 September 2016

Presented by Molly Webster and Robert Krulwich

In this podcast, Radiolab presenter Molly Webster explores the origins of the 14-day rule, which is the internationally agreed two-week time constraint on growing embryos in a lab. 

At the start of the podcast, Webster admits to her co-presenter Robert Krulwich that she had not realised that it was even possible to grow embryos in a lab, and I found her naive perspective a useful one from which to explore the history of the 14-day rule.

We are taken back to the 1970s, when there had been a number of advances in reproductive science – there was the birth of the first IVF baby and progress in genetic engineering. These advances raised contentious questions about the human embryo and when life begins. In the US, there had also been the Supreme Court ruling in Roe v Wade, which determined that a fetus is not a person. This historical rundown will be very familiar for anyone listening with a bioethics background, but it highlighted how these issues have been around for decades and perhaps will never be settled.

We then get to 1973, and are introduced to ethics graduate Leroy Walters, whom Webster introduces as the 'father of the 14-day rule'. I found it interesting to learn that the origin of the rule was rather arbitrary. Walters had been asked in an ethics advisory meeting where he would draw the line for research on human embryos. He suggested 14 days for three reasons: first, prior to this point, around 50 percent of embryos are lost from the wall of the uterus; embryos at this stage can still split into two embryos and so they can be said to lack a 'biological identity'; and the so-called primitive streak – the first structure in the embryo – was thought to appear at this stage. (Although at that time no one had actually seen a human embryo developing past seven days, as Webster points out.)

The committee decided that Walters' 14-day suggestion was appropriate, and submitted it to the Secretary of Health, Education and Welfare. And so the 14-day rule was born.

The rule has stood the test of time over the last four decades, but that was perhaps because, in practice, it never imposed much restriction on researchers – they hadn't succeeded in growing embryos for this long. This is no longer the case. Webster describes, with excitement, her visit to the embryology lab of Professor Ali Brivanlou at Rockefeller University. Here they grow embryos right up until the 14-day mark. Webster describes the 13-day embryo as looking like the light shining through a pinhole in a sheet of paper rather than the 'tiny little human' of Krulwich's imagination.  

Webster is shown images of the embryo developing day by day. While her descriptions of the images are interesting, I thought the podcast could have done more to help us fully appreciate them. The Radiolab web page does have an image of an embryo at day 12, where one can see placental cells emerging, but I would have liked to have seen the progression from days one to 13 for myself. One of the main learning points from this research is that the embryos are able to grow normally without any maternal input up until day 14 (an 'anti-Mother's Day message', Webster jests).

She describes the peculiarity of the researchers' situation – on coming into the lab each morning, they are hopeful that their embryos have managed to survive another day in vitro. Yet, as Webster suggests, eventually this hope would turn into caution. There would be a stage when they may begin to feel uncomfortable to keep growing an embryo in a lab.

Overall, the podcast was an informative introduction to the issues surrounding the 14-day rule and the moral status of the human embryo, and Webster manages to make these complex issues accessible to a lay audience. Right at the end of the podcast, the question of whether the 14-day rule should be altered is finally introduced. This was a shame because I would have welcomed an exploration into whether the original reasons for drawing a 14-day cut off point are still pertinent today. This would have made for a more satisfying ending to what was otherwise an interesting and enjoyable podcast.

12 April 2021 - by Beatrice Costa 
Should research on human embryos be permitted beyond 14 days?...
23 January 2017 - by Rachel Siden 
In this podcast, Professor Magdalena Zernicka-Goetz and Sarah Norcross discuss the current UK ban on researching human embryos in the lab for longer than 14 days...
9 January 2017 - by Dr Valerie Shaikly 
The second session of the Progress Educational Trust's annual conference 'Rethinking the Ethics of Embryo Research: Genome Editing, 14 Days and Beyond', looked at new embryo images that have potential to challenge the 14-day rule and discussed the potential benefits of extending the rule beyond the existing time limit...
19 December 2016 - by Dr Cathy Herbrand 
Baroness Mary Warnock was the first speaker at this year's Progress Educational Trust Annual Conference. She is best known for The Warnock report, which was written more than 30 years ago and has shaped legislation in the UK and around the world...
25 July 2016 - by Wendy Suffield 
Should the current 14-day limit for growing human embryos in the lab be extended in light of recent breakthroughs? This was the question posed in the Guardian's Science Weekly podcast following news that embryos have been successfully developed for 13 days...
23 May 2016 - by Dr Calum MacKellar 
Prohibiting what is useless and legalising what becomes useful in embryonic research without any in-depth ethical consideration may be pragmatic, but such an approach is ultimately just as irrational and meaningless as the concept of the human embryo's 'special status'...
16 May 2016 - by Dr Helen O'Neill 
Species-specific differences in terms of developmental timing and molecular expression patterns have restricted our true understanding of early human development...
9 May 2016 - by Julianna Photopoulos 
Scientists from the UK and US have grown human embryos in the lab for 13 days after fertilisation – the longest ever recorded. This is beyond the stage when embryos would normally implant in the womb, but just before the 14-day legal limit in the UK...
9 May 2016 - by Julian Hitchcock 
The advances of Magdalena Zernicka-Goetz, the opportunities to undertake valuable medical research and our changed sense of values all demand that we reappraise the 14-day limit...
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