An Uncomfortable Scenario

As a follow on from the previous blog about human evolution and cultural buffering, I wanted to play out some hypothetical, and possibly uncomfortable, future scenarios. One question I asked myself, as others have like Isaac Asimov in ‘A Choice of Catastrophes’, is what if we ‘buffer’ ourselves too much from nature? Are there any risks? Specifically, I am referring to the build up potentially deleterious mutations in a world where negative selection and so called purifying selection is significantly reduced. 

    To help explore this scenario I would like to introduce an analogy: Each successive mildly deleterious mutation adds another small item of baggage to the pack on someone’s back (this represents our genetic mutation load). As this pack grows in weight, another helium balloon is tied to it so masking the weight for the person and allowing him/her to go about their business (these balloons represent our clever cultural buffering). Now in this scenario I’m sure you can envisage a few things that could go wrong, besides having difficulty fitting through doors.

    Scenario 1: There is the dramatic case of a number of balloons being burst at once. In this case, people are quickly overloaded and are at risk of being crushed. Now selection would get to work and many people would find it all too much and collapse under the weight of their pack whereas a lucky few will by chance be better adapted to cope with the extra weight, will survive and reproduce children also able to cope. Now this scenario is frighteningly a distinct possibility with the rise of antibiotic resistant super bugs and the potential ‘post-antibiotic era’. Antibiotics have played a HUGE role in extending life expectancies and helping people fight off infections for the last 100 years or so. In our analogy, we are flying a model helicopter blindfolded around our balloons. Given our current reckless use of antibiotics in both medicine and agriculture, it is only a matter of time before we crash into our bunch of balloons unless we remove the blindfold and carefully land that helicopter safely on the ground.

    Scenario 2: A less dramatic scenario, but perhaps more insidious, is if we consider what happens when the production of new helium starts being outstripped by the weight we add. In this case we will reach the carrying capacity of our balloons and not be able to support any more baggage. One possibility here is if the pace of medical progress falters possibly because there is finite headroom into which to advance. One thing about humans, however, is that we have a knack of pulling the rabbit out of the hat with seismic advances in technology and understanding. Another angle is if the mutation rates increase which has been predicted to happen given our increasing exposure to mutagens and even our increasing age of parenthood. This scenario is harder to predict but something like the excellent film ‘Children of Men’ is a possibility. For example our increasing load may reduce fertility levels as the development from egg and sperm to baby is incredibly complex and genetically finely tuned. The increasing levels of infertility may be allowed to grow if families tend to have less children (already the case in many European countries). This would prevent any more ‘fertile’ people having more fertile children to re-populate as they would simply have children younger (or conceive easier) and stop there (using increasingly effective contraceptives, male pills coming soon!) while those less fertile would take longer to conceive, possibly having children later but would also just about reach their quota of one or two. Over time this precess would get harder and harder.

     So what are the possible solutions for our increasingly burdened descendants? Well assuming we navigate global disasters for long enough we might need to fight this hypothetical monster created by our technological advances with… more technological advances! A not too distant reality will be precise and simple genome editing (it is already possible and being carried out in human cells for research purposes in China and the UK with, suitably enough, a view to understanding infertility). Combined with a deeper understanding of what genes do, we could simply correct serious faults. Now I know this is a can of worms with enough ethical dilemmas and many obvious problems so I’ll leave it here and let that be a discussion for our future wiser selves. Yeah right.

UPDATE:  A recent study has demonstrated how caesarian sections have likely resulted in an increase in women with birth canals too narrow for natural birth. This represents a good emerging example of the issues discussed here. Before caesarian sections, women with narrow birth canals (due to narrow hips) would frequently die in childbirth often along with the child meaning the genes for narrow hips were 'purified' from the gene pool. Now, quite rightly, these women are given a chance not only to survive childbirth but keep their children who may well inherit the narrow hip genes. The modest 10 to 20% increase in the prevalence for narrow birth canals over the last 50 years is likely to rise still further given the medical necessity to save lives and the right and desire for women to have children. If we imagine a hypothetical scenario in which caesarian sections can no longer be performed (such as if antibiotics could not be relied upon) then we could see a widespread return to women dying in childbirth or such women avoiding childbirth completely as the buffering effect is lost!

Human evolution and cultural buffering

You may have occasionally heard the idea that humans have stopped evolving which, in short, is not true. Such a belief is likely due to a misunderstanding of the science which I won’t go into in much detail of it here but rather try and explain some interesting processes people are actually referring to. I will, however, give a minimal overview of (human) evolution but bear in mind that evolution is a highly complex topic with many subtleties not remotely covered here. So with that in mind, here is Dr Blur’s overly simplistic definition of the day:

    Evolution is a process whereby a population genetically changes over time. An individual cannot ‘evolve’, it is only through genetic changes that occur in your sperm and eggs and the subsequent mixing of parental genes during reproduction that makes the offspring genetically unique. This needs to be occurring in a population in which the frequency of various mutations (known as alleles) changes – this is evolution. This can be directional or not. A directional example might be for evolving taller in which various mutations that encode taller people spread throughout the population over successive generations (i.e. goes from novel, less frequent to most frequent). Now we have taller people, yay.

    As mentioned, evolution need not be directional and this is the topic I would like to discuss in the context of contemporary and future human evolution. When people talk of humans no longer evolving, they are likely (know it or not) talking about this non-directional evolution. This is particularly prominent in humans due to what is known as ‘cultural buffering’. This is a concept that I think is clearest illustrated by the example of clothing. Clothing was a human ‘cultural’ (behavioural/non-genetic) invention some many thousands of years ago that enabled the colonisation of colder climes (think inuits and the sami) but it also played another important role: as a ‘buffer’. Clothes might have enabled skinnier people to survive in colder environments, assuming having more fat was advantageous. In essence these otherwise less adapted people are buffered against the harsh ravages of nature and can survive to reproduce when before the 'cultural buffer' (clothes in this case) they would not have.

     Therefore a technical model for cultural buffering is that is reduces the negative selective pressures on deleterious mutations.

      This reduces the effect of so called ‘purifying selection’ which, despite sounding like something out of Nazi Germany, is an integral part of natural selection which sculpts and refines species to their habitats and challenges. Interestingly, such a relaxation of selection (e.g. you don’t need to keep that layer of fat any more) can also lead to directional evolution. Imagine that storing that extra fat or any other trait is energetically expensive, then mutations that used to be deleterious (e.g. not being able to put on fat) now become advantageous as they don’t waste energy so now you can use that energy for your brain development for example. This actually also relies on another factor, a limited supply of energy in the first place! Without this constraint (which is largely the case in the calorie rich western world), there actually is no benefit either way and so whether you put on the fat or not means nothing: the clothing keeps you warm on one hand and you can easily afford to make that fat layer AND develop your brain on the other. The general trend, however, will always be to accumulate errors (warning: data corrupted) as with buffering there is less pressure on removing these genetic corruptions.
    So, now to some modern examples to explore this idea a bit more and what better example than the marvel of modern medicine! Sadly only a marvel for those with access to it of course. Modern medicine has extended life expectancies and allowed the survival to reproduction of many people who otherwise might not have. Some interesting examples include type 1 diabetes (the genetic one, not the one heavily linked to an excessive sugar diet and consequent insulin resistance) and cystic fibrosis (CF). People born with these conditions in the past would rarely live more than a few years and would certainly not survive to reproduction but now can lead relatively normal (but by no means easy) lives into adulthood and potentially parenthood. Being genetic, these conditions can be passed on to offspring with a CF parent having a ¼ chance of the child also having CF while type 1 diabetes is more complex. Of course many people that now survive when they might not have before go on to contribute significantly to society and as such I certainly don’t see this as a bad thing – the genetic lottery can be cruel and unforgiving. In many ways you can view cultural buffering as the great leveller neutralising the effects of this lottery.
    So, we have not stopped evolving, we have simply become more insulated from the world around us. Mutations still occur between generations, some 100 new ones per baby, it is only that increasingly less of these mutations might be under any particular selection. When previously some of these could have proved detrimental, they are now tolerated. Cultural buffering is a very human feature; a product of our large brains, curiosity and language and will only become a greater definer of who and what we are. While I may have implied cultural buffering allowing ‘bad genes’ to spread is not necessarily a bad thing, although social Darwinists might disagree and in fact many misinterpret Darwin’s theory for their own benefit. Who’s to say a mutation is bad anyway if we can find a way to tolerate it and allow a human a healthy life. As far as evolution is concerned, a deleterious mutation ceases to be deleterious if it is no longer selected against. Another aspect of human evolution, and evolution in general, I have not covered is sexual selection which might be something for another time.

I explore the future of this subject here.