Two days ago, Matt Ridley published a rhetorical editorial in the Wall Street Journal‘s column Mind & Matter. Ridley addresses the decline in incidence of inheritable diseases, overcoming infertility with in vitro fertilization (IVF), and other topics such as the impact of culture and brain expansion. The piece has gained a lot of attention in social media with over 1,900 Facebook shares and 650 Tweets at the time of writing this blog post. This is poignant discussion to be had but Ridley’s assessment falls short.
Ridley discusses relaxed selection by bringing up an IVF technique, intracytoplasmic sperm injection, used help men with immotile sperm to father children. Firstly, since he didn’t mention the cause of immobility of the sperm, I must mention that in any given man a significant portion of sperm are immotile. The ratio of immobile sperm to motile sperm is critical, as is the volume of or sperm count. The WHO standard for motility of sperm is about 50% of the sample, any less than the risk of infertility rises. However, if the sperm count is high, then having less than 50% motility is not an issue.
There are certain circumstances where almost all sperm are immobile, such as Kartagener’s syndrome. Kartagener’s syndrome is a primary ciliary dyskenesia. This is an autosomal recessive genetic disruption in the arms of the motor protein dynein. Kartagener’s syndrome is approximated to be present in 1 out of 15,000 – 32,000 men., of which infertility is not a primary concern. I write this because main result of impaired ciliary function is the impairment of clearing mucous to the lungs. Chronic respiratory infections due to progressive damage to the respiratory system, leads severe diseases like bronchiectasis beginning in early childhood. Prevention of these complications is more important than using IVF.
Ridley weakened his argument on relaxed selection, because he failed to discuss the details of what sperm immobility is and means. Furthermore, in an example of true spermatic immobility, surviving to reproductive age when respiratory complications hit is low. Why didn’t he address the relaxation on selection with the increase use of C-sections?
In the next half of the article, I can’t tell if Ridley was playing Devil’s advocate with this excerpt,
“Now, thanks to pre-implantation genetic diagnosis, parents can deliberately choose to implant embryos that lack certain deleterious mutations carried in their families, with the result that genes for Tay-Sachs, Huntington’s and other diseases are retreating in frequency. The old and overblown worry of the early eugenicists—that “bad” mutations were progressively accumulating in the species—is beginning to be addressed not by stopping people from breeding, but by allowing them to breed, safe in the knowledge that they won’t pass on painful conditions.”
Parents are still giving birth to children with known and unknown deleterious mutations. Post-implantation diagnosis of genetic diseases with techniques like such as amniocentesis or chorionic villus sampling are not offered to all expecting mothers, nor do all expecting mothers chose to these tests… Let alone pre-implantation! To say that these this practically non-existent option has directly caused a decrease deleterious traits to no longer be selected against is a bold and brash statement. The increase in admixture is a more impactful variable in the reduction of incidence in genetic diseases the pre-implantation diagnosis.
Ridley also brings up the differences of SNPs seen between people of European and African ancestry, attributing nothing of substance to the observation that Europeans have half as many SNPs as Africans. He implies, “larger population allow more variants [with] less severe selection against mildly disadvantageous genes,” and attributes the expansion of population in the last 5,000 years to this. But within a species, mutation rates are constant, regardless of the selective pressure.
Lastly, commenting on the slow rate of brain expansion and how modern advances in technology and culture will have an effect on evolution is akin to equating how the Kardashians will effect the Sun’s eventual implosion. The sum of the pressures of selection occur with drift. The time frames of history, in the thousands of years are too small to capture this phenomenon. A genetic example to outline this, is the Black Plague. European communities show much lower genetic diversity because of mass death that wiped out large populations, it had almost a nil effect on our genetic traits as a whole.
Like any progressing variable, time and culture offer different selective pressures upon the evolution of humans. While on one hand we maybe selecting for people with deleterious traits by offering IVF and C-sections to those who wouldn’t normally become parents, we on the other hand can prevent the births of offspring with such traits by early diagnosis. Additionally, as our population continues to expand and cultures admix, can we with certainty say we see an impact on the genetic and phenotypic makeup of humans?
These questions lead me to ask, “What Should Human Evolution Be?”