Over the past 4 billion years the process of natural selection, through its method of patient, plodding persistence has gradually honed us Homo sapiens into the remarkable species that we are today.
Yet this same blind, unthinking mechanism also poses a seldom considered, yet very real problem to the future of our kind which could, if left unchecked, pose a serious threat to our continued prosperity.
In this article, I will illustrate the necessity of our eventual scientific manipulation of the human genome, in order to prevent the gradual deterioration and loss of many vital human traits.
I often find myself looking at a person – and glimpsing, for a few profound moments, their true, atavistic nature – realizing that they are but a single branch of the sprawling tree of life – apart, somehow, from other organisms on earth – yet still intimately, inextricably connected with their evolutionary past.
Surrounded by man-made structures of concrete and symmetry; isolated in our hermetic paradise from the dangers of nature, it can be so easy to forget that we too are mere animals – forged by the same brutal environment that also gave rise to sharks, rats, and lions.
Similarly, it is easy to lose sight of the fact that we are still very much under the sway of the biological mechanisms that allow for the process of natural selection to occur – namely, the small, random mutations of our genes (as well as the recombination of genetic material via sexual reproduction) from generation to generation. This process has not somehow magically ceased since our supposed decoupling from the rest of nature – and we are thus still subject to its influence.
This then motivates the question: what kind of human phenotypes might be altered in the future, given our current swaddled evolutionary environment of safety and abundance? What traits might provide one human with a survival/reproductive advantage over another, and so be selected for?
It turns out, this is very difficult to conjecture about, simply because it is almost impossible to predict the changing landscape of human existence over the coming decades, let-alone centuries. Will our survival come under threat from some unforeseen environmental change – perhaps favouring those humans with, say, an improved respiratory system? Will the dynamics of sexual selection be altered to any significant extent – leading for example, to the predomination of men with small noses and large beards? Who knows?
Yet despite this uncertainty, it is actually possible to make a few predictions with some degree of confidence – and these are each based on the same principle:
‘Relaxed Selection’ – AKA ‘Use it or Lose it’
In order to illustrate the principle, we’ll first consider the Kiwi bird, which is native to my country of New Zealand.
The Kiwi is presumed to have flown to New Zealand some millions of years ago, whereby it found itself happily ensconced upon a peaceful little island that was utterly devoid of predators.
The Kiwi was now able to roam the terrestrial realm (which would have been a mortally dangerous activity in its former biome) with sheer impunity – gorging itself on the multitudes of insects that abounded the forest floor.
The birds had soon completely shunned the sky and the trees – and so too their need to fly.
Today, the wings of the now flightless birds are almost non-existent – having become a pathetically stunted remnant, about the size of a thumb. With no environmental pressures to select for wings, they were at the mercy of what is known in evolutionary biology as ‘relaxed selection’. ¹
Another case of relaxed selection is observed in deep-sea fish, which live beyond the purview of sunlight, in pitch-blackness. Without the need to see, their eyes have deteriorated into useless globules, lingering uselessly on the side of the fishes’ faces as an ironic wink to their past glory.
We can explain the mechanism through which a phenotype gradually becomes obsolete by considering what’s happening from the point of view of the genetic code:
Given that random mutations within the DNA of successive generations of a species are inevitable, the genes that give rise to any given phenotype will eventually develop ‘errors’.
In the case of phenotypes that are important for the creature’s survival/reproduction, these errors would die off with those individuals unfortunate enough to have inherited them – leaving the surviving generations error-free.
Conversely, for phenotypes that lack any selection pressures (such as wings, in the case of the New Zealand Kiwi), the errors will continue to accumulate and propagate, as father passes it on to son, and so forth – over time rendering the trait completely defunct.²
A thoroughly interesting 1997 experiment showed precisely this phenomenon.
The experimenters began with a population of fruit flies, which were kept for 30 generations under ‘relaxed selection’ conditions.
In each generation, male and female flies were assigned randomly to pairs, and each fertile pair contributed a son and daughter for the next generation – thus any type of sexual selection was made impossible.
The flies were allowed to live in conditions of luxury – with ample food at hand, and no predators to fear. For these flies, life was good – they wanted for nothing, and so natural selection loosened its guiding reins on certain of their genes.
What would happen then, if they were to be reintroduced to ‘the real world’ – where life for a fruit fly isn’t quite so comfortable?
As anticipated, each subsequent generation from the experiment was less apt to survive than the one before it. Relaxed selection had taken its toll.
So what does this mean for us?
Our lives, much like the fruit flies in the aforementioned experiment, could well be considered luxurious.
In this age of modern technology and medicine, many genetic handicaps that in the wild would have spelled certain death, are now little more than slight inconveniences.²
Consider the human eye, which has maintained almost that same complex structure for millions of years – its genetic code so sublimely wrought that natural selection has seen it preserved and propagated ever since it was perfected. Any unfortunate offspring whose ‘eye genes’ weren’t quite up to spec would have had a difficult time distinguishing predator from prey, and consequently their malfunctioning genes were unlikely to have been passed on to the next generation.
But now, in the modern era, if a genetic ‘error’ happens to impair a person’s eyesight, they can simply (in many cases) seek the help of an eye doctor, and slap on a pair of prescription glasses or contact lenses.
Their genes are no less likely to propagate into subsequent generations than their neighbor with 20/20 vision – since they will be just as capable of surviving long enough to reproduce and raise their children.
Over time, the genetic errors associated with poor eyesight could therefore aggregate within the genetic pool of human populations. So how many generations before we’re all stumbling around in a bleary-eyed haze?
The same principle applies to any other human faculty that, should it experience a deleterious genetic mutation, can be either artificially aided by modern medicine, or simply has no bearing on survival and reproduction in our present environment.³
Hearing, smell, taste – even certain aspects of intelligence – none of these are safe. The selection pressures that would once have fostered these abilities – dangerous predators, the need to locate and recognize edible foods, the need to memorize a plethora of plant species – are now gone, rendering us, to a certain extent, fruit flies in a cage.
Assuming that human-kind is able to improve, or even simply sustain its present environment of relative comfort, then it is not a question of if relaxed selection will begin to manifest disabilities in future generations, but when.
It is imperative then, that we eventually develop a means of tweaking our own genetic code – of playing God – so that these most revered and essential human capacities can be safeguarded, for the benefit of our collective future.
A supplementary write-up for this article has also been written here.
 It should be noted that in the case of the kiwi (and deep-sea fish), along with many others found in nature – there can in fact be selection pressures that actually cause the losses – for example, as a means to reduce unnecessary energy expenditure of the organism. Strictly speaking then, the loss of traits in such cases are not solely caused by relaxed selection.
 I’ve gone into some interesting detail about human sexual selection regarding disabilities here (short article)
 This addendum also addresses another detail that was overlooked in this article – that there remain human populations for whom life is far from easy, and who would not experience the effects of relaxed selection to anywhere near the same degree as those in first-world countries.