It might sound silly to claim that evolution has stopped, but some that I’ve discussed this with at times have suggested it might be the case. The thinking is that natural selection no longer kicks in because we now step in with modern medicine and so those who would not have been previously naturally selected now survive and breed. Is this true? Some think so. OK yes, that is a link to the Daily Mail, and requires a large gain of salt to digest, but my point there with that link is not to suggest this is true (or not), but rather to simply illustrate that some do indeed suggest evolution has now stopped for humans. I personally don’t hold that view.
So what is new?
An article entitled “Natural and sexual selection in a monogamous historical human population” has been published that examines this issue.
Let’s cut to the chase, what is the conclusion? “humans are continuing to evolve and that significant natural and sexual selection is still taking place in our species in the modern world”
Ooooh interesting, so how did they come to that conclusion? Well, the folks involved over at Sheffield University have a nice little summary (press release) that tells all, so any media stories (such as this one here) will have used this as a source. In other words, this is patient alpha for the various news articles that relate to this. They write …
Scientists in an international collaboration, which includes the University of Sheffield, analysed church records of about 6,000 Finnish people born between 1760-1849 to determine whether the demographic, cultural and technological changes of the agricultural revolution affected natural and sexual selection in our species.
Now that date bothers me a bit, as does the observation that it is just Finland, but the press release does acknowledge this. The Project leader, Dr Virpi Lummaa, is quoted as saying …
“We have shown significant selection has been taking place in very recent populations, and likely still occurs, so humans continue to be affected by both natural and sexual selection. Although the specific pressures, the factors making some individuals able to survive better, or have better success at finding partners and produce more kids, have changed across time and differ in different populations.”
What is also interesting is that it did turn up a couple of surprises. For example, the finding that “selection affected wealthy and poor people in the society to the same extent”, I would not have anticipated that.
You might wonder why Finland, well apparently genealogy is very popular in Finland and so the country has some of the best available data for such research. They not only tracked the obvious details such as birth and death facts, but also recorded wealth status (for tax reasons apparently). As a real bonus they also had stability, because people tended not to move about very much prior to the 20th century.
So exactly how big was their data sample?
What did they Observe?
Individual differences in early survival and fertility (natural selection) were responsible for most variation in fitness, even among wealthier individuals. Variance in mating success explained most of the higher variance in reproductive success in males compared with females, but mating success also influenced reproductive success in females, allowing for sexual selection to operate in both sexes. The detected opportunity for selection is in line with measurements for other species but higher than most previous reports for human samples.
It is all indeed very interesting, but what does fall out of this are a couple of immediate and very obvious questions:
- The study relates to people born between 1760-1849. Since 1849 medicine has greatly advanced, and so that would have perhaps potentially altered things quite radically. I have no evidence that this is actually true, I’m just speculating out loud.
- I also note that the study is specific to Finland, so I also wonder if the conclusion would hold true for other populations. In other words is this just specific to Finland?
The Paper Itself
If you go to PNAS, the paper is behind a paywall … (ugh!) … ah but some good news. One of the paper’s authors very kindly shared a copy of it with me, so if you would like to read it all, then you can, here it is …