Overselling Human Evolution: The Finnish Edition
Recent and well-publicized research looking at a Finnish population of 5,923 individuals, born between 1760 and 1849, has confirmed that humans are still capable of "evolving." Whatever exactly that means.
Media headlines make it all sound very exciting: "Humans really are still evolving, study finds" or "Darwinian selection continues to influence human evolution." Unfortunately, while the actual research article in PNAS ("Natural and sexual selection in a monogamous historical human population") demonstrates that humans are capable of evolving, it did not show definitive data to indicate they have evolved or did evolve. The media airbrushed over that wrinkle in the story, but the article itself, to the authors' credit, addresses this criticism and specifies why the research is still of interest.
From the abstract and the article:
Our results emphasize that the demographic, cultural, and technological changes of the last 10,000 y did not preclude the potential for natural and sexual selection in our species.There are several possible responses: What does "humans are capable of evolving" mean? Why do we care? Was there some reason to believe humans had stopped evolving?
We recall that measuring the opportunity for selection does not necessarily equal measurements of actual selection acting on traits other than fitness.
Let's consider that last question first, because it provides the context for the discussion. Some scientists argue that advances in medicine, agriculture, and technology as well as lifestyle choices, such as monogamy, may have stifled human evolution. From such a perspective, if a researcher wanted to study human evolution, he would have to look at pre-industrial humans. Essentially, this view says human beings are no longer evolving like animals in the wild do because our innovations allow us to withstand environmental pressures that humans prior to industrialization could not withstand. The implication is that humans are tampering with the environment so that environmental pressures that otherwise select for fitness are, in fact, rendered tame. This leaves human evolution to stagnate.
Also implied is that human innovation is not part of the evolutionary process. This was not addressed either in the research article or in media reports, but one notes the underlying assumption that human innovations in technology, agriculture and medicine somehow don't "count" as adaptations to the environment. Yet insect and animal innovation does count as evolutionary adaptation. According to evolutionary theory, humans are ancestrally related to animals, and are therefore different from animals in degree, but not in kind. Shouldn't our innovations be weighed in the same scale as animal innovations? For whatever reason, it seems not.
What follows from this is the next question: Why do we care? Conspicuously left out of the media coverage is any value statement as to whether human evolution is a good thing or a bad thing. In other words, are we glad that humans are still (capable of) evolving or not?
The implication is that this is a good thing. With medicine, technology, and agriculture, weak people are surviving long enough to breed. This allows less robust traits to propagate through the population because natural selection has, so to speak, been tamed. Furthermore, it was formerly thought that certain cultural norms, such as monogamy, preclude the possibility of sexual selection. Implied in these reports is that, despite our best efforts, natural selection and sexual selection are tougher than our attempts to stifle them.
Lest this sound like we're reading too much into the media coverage, see this MSNBC article:
Natural forces of evolution still continue to shape humanity despite the power we have to profoundly alter the world around us, researchers say.One of the purported benefits to come out of this type of research has to do with advancing medical therapies. The idea is that understanding how humans adapt to their environment can help us understand how our immune system will respond to disease or epidemics. This would aid researchers in drug development and controlling epidemics. But this justification seems a bit trite, sort of a "tacked on" notion since the point of the article is that our best efforts to control our environment do not stifle natural selection.
Evolution occurs in response to outside forces that weed out whatever individuals are least fit to survive those pressures, allowing those better-fit individuals to survive and reproduce. However, since humans radically alter their environments, some researchers have questioned whether natural forces of selection continue to act upon our species.
Finally, we come to the first question posed: What does this all mean? Are we supposed to think a new race of humans will emerge? Or, that we don't have to worry about the weak diluting our gene pool? This is probably the most confusing part about the research.
The confusion stems from what is meant by evolution. When a report states "humans are still evolving," what does that mean? When people speak about evolution, they may be thinking of any number of definitions, from adaptation to the environment through natural selection to survival of the fittest to the emergence of a new species through reproductive isolation. They may also be thinking of definitions that are based on extrapolations from the data but are not necessarily observed, such as: All known organisms are descended from a universal common ancestor, or natural selection coupled with mutations has lead to the emergence of all life that we see today.
Some scholars say the word evolution has ten separate meanings, an ambiguity that Darwinists habitually use to their advantage when addressing the public; others narrow it down to three meanings. Some definitions overlap. The point is that "evolution" or "evolving" can mean a variety of different things. Some of these are potentially observable, and some are extrapolations based on certain assumptions.
The authors of this article define the ability to evolve as a condition where natural and sexual selection are still capable of acting on a population. Their studies looked at four criteria:
Specifically, we studied the contribution to the opportunity for total selection of four different episodes of selection during the life cycle: survival to reproductive age, mate access, mating success, and fertility per mate.Natural selection still occurred because a certain percentage of the Finnish population did not survive beyond age fifteen. Sexual selection also occurred, despite the subjects' practice of monogamy, as the authors saw by looking at reproductive success, mating success, and the Bateman gradient, which assumes there is a strong association between mating and reproductive success. The research included studies with multiple marriages due to the death of a spouse, and the number of children per spouse.
The authors found that in the population under consideration there was a difference in fitness between men and women, likely due to men remarrying younger women who were still within reproductive age, while widowed women tended to be beyond reproductive age. They also found that there was no difference in natural and sexual selection between landowners and non-landowners (i.e., wealthy and not wealthy).
Essentially, the authors are saying that because the fitter (or better adapted) people survive and the more fertile have more children, humans can still evolve. Furthermore, sexual selection still occurs, though to a limited extent:
Most of the variation in relative fitness resulted from two episodes of selection that correspond to natural selection: survival to adulthood and fertility. Nonetheless, sexual selection was also potentially effective; this was true even among women who, in sharp contrast with men, did not benefit from multiple pairings.If evolvability is defined this way, then obviously humans are still evolving -- if we are reproducing, then we are evolving; if people are dying, then we are evolving. This is not saying anything novel.
This research is interesting, particularly in the way it looks at how the average number of children was not different between genders or among the landowners versus compared to non-landowners. But to tout this as some kind of discovery about human evolvability is, to say the least, an oversell.
Photo credit: Finnish folk dancers, Irmeli Aro/Flickr.