Saturday 31 August 2013

Are Humans Devolving?

I occasionally come across people arguing that advances in modern science and technology have halted human evolution and that we are now devolving as a species. The basic argument goes something like this: millions of people who would've died because of allergy, disease, birth defect, injury, etc. now survive and reproduce. Therefore, their weaker genes are contaminating the human gene pool and we've defeated natural selection. Sounds reasonable, right? Everyone's familiar with the phrase "survival of the fittest". The survival of weaker people must be a bad thing. 
And this will probably happen. It's "science". 
This argument bears striking resemblance to the reasoning used to justify various compulsory sterilization and euthanasia programs of the early 20th century. However, eugenics has largely disappeared and is now widely considered to be immoral. The Charter of Fundamental Rights of the European Union prohibits eugenics-based practices explicitly. Though the immorality of eugenics doesn't refute the argument that humans are devolving, perhaps it is a clue that the reasoning behind eugenics is flawed. 

I haven't actually taken any biology courses, so I'm probably unqualified to address the devolution argument, but it seems to me that it indicates an oversimplified view of what evolution really is. Suggesting that we no longer evolve is basically saying that humans are a special class of life that breaks all the rules when it comes evolutionary biology. In which case, the theory of evolution requires some significant revision to account for the anomaly that is humanity. 
Aside: I hope that no creationist cherry-picks this blog post for anti-evolution causes.
The phrase "survival of the fittest" is an elegant way to describe natural selection, but perhaps it does so too succinctly and is too easily misinterpreted. The argument that because we co-operate to cheat death we've somehow halted our evolution inherently assumes that "fitness" refers only to physical strength and robustness. When Darwin used the phrase, "fittest" was intended to mean "best adapted for life in their local environment". 

Physically weaker members of a species often still reproduce. In fact, this probably contributes to the species' overall viability by increasing genetic diversity. There is a misconception that in species living in hierarchical groups controlled by alpha males, the alphas do all the mating and all the other guys die bachelors. While alpha males typically mate far more frequently, other males still manage to sneak in a few trysts to pass on their genes. You might say that having the cunning to pass on genes despite inferior strength indicates greater intellectual fitness. Brain overcoming brawn. Clearly, physical fitness is not the only way for a species to survive and reproduce in its environment. 

To elaborate on the importance of intellectual fitness, let's look at tool use. We've mastered the use of tools, but we are not uniquely endowed with this ability. Sea otters use rocks both for prying abalone and to break open their hard-shelled prey. Chimpanzees use sticks to fish for termites, sharpened sticks to spear Senegal bushbabies (which are nocturnal primates, not Senegalese infants), and stone hammer and anvil to break open nuts. Capuchin monkeys also use stone hammer and anvil to break open nuts and seeds. Elephants use sticks to swat flies and chewed up tree bark to plug holes dug for groundwater (preventing evaporation). 
In addition to bashing shellfish with rocks, sea otters do adorable things like hugging their offspring.
Animals capable of tool use have evidently benefited from intellectual fitness during their evolutionary history. Some of these animals would probably not survive if tools were suddenly unavailable today. Yet believers in human devolution don't seem to think that sea otters are also devolving because a lot of them would starve to death if appropriate oyster-smashing rocks became unavailable for some reason. Antibiotics and epi-pens similarly don't reverse human evolution simply because some of us couldn't survive without these tools. 

Creatures can evolve traits to better equip them for survival in their environment, but they can also evolve the intelligence to manipulate their own environment to make it more survivable. Tool use is just an example of manipulation of one's environment, something that many living things do to various extents. Gorilla traps are something humans have added to the gorilla environment. The gorillas need not evolve traits to make them more difficult to ensnare because they already possess the intellectual fitness necessary to dismantle the traps and teach this skill to the younger generations. In other words, the gorillas manipulate their environment to remove a threat to the survival of their species. Fundamentally, this is hardly different from the human campaign to eradicate polio
With humans devolving and apes spearing bushbabies and dismantling snares, this scenario is inevitable.
While our ability to manipulate our environment has progressed far beyond the basic tool use seen in the animal kingdom, our quest for survival is fundamentally the same as any other creature's. The fact that we cannot survive outside the artificial environment of our making doesn't mean our evolution has halted. It is the environment humans actually live in that matters, not the fantastical universe where intelligence is eschewed and human survival is decided by physical fitness alone. In the developed world, the reality is we've created an environment where nutrition is optimal, children are (usually) vaccinated against preventable diseases, and antibiotics and epi-pens are readily available. Under such survivable conditions, it is to be expected that physical fitness becomes less important and what might have been "weaker" genes in the past start to make their way back into the gene pool. The belief that the increase in reported cases of asthma and allergies in children in the industrialized world signifies a devolution of the species is misguided. A rise in the prevalence in peanut allergy is simply to be expected wherever peanut allergy becomes more survivable, because the genes responsible for the condition are no longer a significant threat to fitness. 

Our abilities to co-operate and to manipulate our environment, i.e. our intellectual fitness, serve us far better than our physical fitness today. I think the expectation should be that humans will gradually become smarter as a species while simultaneously making the human environment increasingly survivable. It's what we've been doing for all of documented history (and for a long time prior, too). That hardly seems like devolution to me.