EVOLUTION AND IVF

Assisted reproduction and its role in human evolution

Published 17 July 2019

Since its invention, IVF has been controversial because it enables infertile people to bypass barriers to natural reproduction. Fertility treatment allows traits - even disabilities - to be passed on to the next generation from couples who would otherwise have been unable to create offspring. But does this mean that IVF and other techniques are influencing human evolution?  

That was the topic of a lively head-to-head debate in Vienna between Hans Ivar Hanevik from Sykehuset Telemark in Porsgrunn, Norway, and Soren Ziebe from Rigshospitalet in Copenhagen, Denmark.

Arguing the case for IVF'S hereditary influence, Hanevik emphasised how fertility treatment creates 'selection pressure', which in itself is essential for evolution to take place. However, the type of pressure derived from IVF is quite distinct from the pressure which nature requires to create offspring. This is illustrated, he proposed, by women having to lose weight in order to meet the eligibility criteria for ART in some parts of the UK, or IVF embryos needing to advance to the 4-cell stage of cleavage division to progress.

In ICSI, the influence of fertility treatment on evolution is even more evident. Sperm must be motile and able to swim long-distances for reproduction to take place in nature. But none of that is necessary in ICSI. 'A systemic difference exists between what happens in nature and in fertility treatment,' Hanevik said. 'If you change selection pressure, then you must be influencing evolution.'  

However, Hanevik conceded that data on the long-term impact of IVF is lacking, which makes it hard to predict any real-life evolutionary consequences. Studies have suggested a link between ICSI and lower semen quality in boys, although he emphasised that these risks should 'not be a barrier' to treating people. Indeed, lazy sperm cells that have lost the ability to swim long distances may turn out to have other advantages - it's simply that we don't yet know what they are.

Taking the opposing viewpoint, Soren Ziebe pointed out that the number of ART babies born over the last few decades compared with those naturally conceived was not enough to alter the world's gene pool. In addition, it takes around 1 million years for any lasting effects of evolutionary changes to be demonstrated. So there is a long way to go before any impact of IVF on humanity might be proven.

However, on a positive note, Ziebe agreed that IVF does have a huge impact on people's lives by changing fate for many families 'who now have a life with children' - even though ART is based on reverting to natural function and correcting errors, not on creating the greater variety of evolution. Natural selection leads to change for the better. But Ziebe said it was hard to imagine any evolutionary consequence of IVF from bypassing blocked fallopian tubes - despite associations with endometriosis or pelvic inflammatory disease.

IVF is not based on a masterplan to violate nature's intended design, Ziebe said, and to illustrate his point insisted that in IUI and IVF there is no design - the oocyte is fertilised by the first sperm cell it meets. Embryo selection too is merely a 'ranking' by which the embryos meet the uterus - unless 'you believe a competent embryo always arrives in the uterus'.  

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