Podcast Review: Sperm — swimming and surviving

Did you know that all successful sperm must be sleek, speedy and streamlined?

As both an avid podcast listener and a scientist myself, I am surprised that this was my first introduction to The Naked Scientists. The group host a plethora of different podcast series, with subjects ranging from neuroscience to astronomy. They release daily short episodes that concisely detail a single topic, as well as a longer weekly flagship podcast.

In this short episode, The Naked Scientist host and medical consultant, Dr Chris Smith, interviews sperm expert, Professor Allan Pacey, from the University of Sheffield. With just seven minutes to detail the focus of his entire academic career, Professor Pacey began by illustrating the structure of sperm, likening their cross-section to a 'stick of rock that you might buy at the seaside'; an analogy that can be appreciated by experts and non-experts alike, setting the tone for a broadly accessible podcast. 

Dr Smith then asked a question that piqued my interest – 'Are they constantly swimming even when they're being made in the testicles?' Professor Pacey explained that they only swim once released, and that their doing so is multifactorial – an elegant combination of 'the removal of the chemistry of the male body and… the stimulatory chemistry of the female body'. 

Professor Pacey also debunked the myth that Dr Smith and I both believed to be true – that millions of sperm manically race from the testicles towards the egg. Interestingly, despite the fact that a man will 'ejaculate 50 or 60 million sperm into a woman… only around half a dozen [will survive to the oviduct].' Only sperm which are A) the correct aerodynamic shape, B) can avoid certain death by female immune cells, and C) can sense chemical signals from the egg, stand a chance of fertilisation. Therefore, 'it's probably only at the last few millimetres of the sperm getting towards the egg that there's actually a sperm-by-sperm kind of race.'

Towards the end of the podcast, Dr Smith directed the conversation in a fascinating direction: how sperm shape varies between monogamous and polygamous species. Professor Pacey explained that 'promiscuity within a species does impose some sperm-specific selection pressures.' In his example, he detailed how chimpanzees are highly promiscuous, and consequently their sperm are 'fast… sleek and elegant.' On the other hand, gorillas are less promiscuous and have 'by comparison… pretty terrible sperm.' 

He concluded by describing humans as somewhere in between our primate relatives. This prompted a thought I had concerning human relationships – do promiscuous men have better sperm than those who are more monogamous? Unfortunately, my question was unanswered, and the podcast appeared to end rather abruptly – so much so that I checked to see if I had lost internet connection. 

I had found the conversation so interesting that I wanted it to continue. However, that is the design of the short daily episodes – they are bite-sized pieces of information devised to grab the listener's attention and maintain it for the duration of the show. I believe that these episodes are perfect for the busy listener in a rush, or someone who is dipping their toe into science stories. However, if like me, you prefer to be immersed in a topic, you might prefer their longer, weekly, episodes.

The longer podcasts, such as 'Movement Science: Devotion to Motion', are styled to take you on a journey throughout a scientific subject, such that you finish in a completely different area to that which you started in. For example, this episode in particular ranged from the new COVID-19 vaccines to earthquakes and volcanoes. These episodes include panels of experts from completely different fields, providing the listener with multiple perspectives on a single topic. Needless to say, I am now a subscriber to The Naked Scientist Podcast series.