The question of whether we are still evolving can be answered if we look at multi-level selection theory. Our continued evolution relies on there being long-standing, not merely transitory, selection pressures which cause individuals with certain mutations to better survive and procreate than others. Because of our large population, any changes will take far more time to predominate than was the case when we numbered in the tens of thousands. Even when accelerated by feedback between cultural and biological evolution, biological change will still be very slow.
Individual Level Selection. In recent years, social values, and norms, e.g., “thou shalt not kill”, have reduced individual level competition. Improved medical, agricultural, and economic practices have significantly reduced the external selective pressures on mankind. On the other hand, globalisation and increasing population density is leading to an increased risk from pandemic diseases. These are highly significant factors in natural selection at the individual level and, together with our reliance on vaccination and other medical technology, they are likely to lead to changes in our immune systems. An example of recent selection at individual level is the predominance of sickle cell anaemia in populations exposed to malaria. When the genes causing this disease are inherited from only one parent, they act as a defence against malaria but, when they are inherited from both, they result in anaemia.
On balance, therefore, it seems likely that natural selection at individual level does still exist but to a much lesser extent than in the past. If so, then natural selection may have shifted more towards the higher levels described below.
Kin Level Selection. We do of course continue to favour our kin, but it is notable that, in the West, the large extended families of the past are in decline and that families are now largely nuclear, i.e., parents and children. There have been several experiments involving raising children outside of nuclear families, e.g., Israeli Kibbutzim, but all have failed. Nuclear families exist throughout the animal world and are strongly established in our genetic inheritance. It is unlikely, therefore, that there will be any change in the future which might lead to genetic adaptation.
Group Level Selection. Global society is moving towards one in which destructive competition between groups is ever more unacceptable. Unfortunately, wars and the abuse of one group by another continue to take place. There also remains an element of cultural competition. However, due to increasing global organisation and centralisation, despite the existence of cultural differences between groups, based primarily and belief, there is also a process of convergence towards a monoculture taking place. We may still be evolving slowly due to group level selection, but again, not at the pace experienced in the past.
An example of human evolution due to group level selection is the gene that controls lactase production. This enables us to consume milk into adulthood. It emerged among tribes with a long history of cattle herding, and appears to be spreading through the global population alongside the consumption of dairy products.
Species Level Selection. Although species level selection may, in the past, have taken place between hominins, Homo Sapiens is now the only one remaining. Our closest relatives are the chimpanzees and bonobos, and we face no interspecies competition for our ecological niche. Different ethnic groups are currently experiencing different growth rates. However, they are all members of one species. Due to globalisation, the finite size of the planet, and ease of travel, there is ever less separation between them. We are almost certainly no longer speciating and, therefore, not subject to species level selection.
Eco-system Level Selection. The human economy is evolving culturally at a very rapid pace and competition between it and the natural eco-systems is fierce. However, it is only enduring changes that will lead to human genetic evolution. An example may be our ability to communicate using technology. Currently, this seems to be the strongest selection pressure on human evolution. Our economy or artificial eco-system is altering the natural environment and we, in turn, are adapting, first culturally, but ultimately genetically, to these changes.
Of course, if an existential catastrophe were to occur, then this situation would change. Those best suited, by random mutation, to the post catastrophic circumstances may survive and continue to procreate. Group separation, and thus speciation, would re-emerge and biological evolution would pick up speed due to new, stronger pressures and the dramatically reduced population. Individual level selection is also likely to come to the fore, once more. We do not know the future nor the genetic mutations that we carry, and so, cannot predict the outcome. However, some of the risks that we face are clear. Climate change and failure of food supply are two examples. It would, therefore, be sensible to act now to eliminate these risks.
This is my final post on evolution. I hope that you have found it interesting. In my next post, I will begin a series on human needs and how they motivate our behaviour. This next series is underpinned by the evolutionary theory discussed so far.