Evolutionary selection is a result not a cause. It is a result describing the genetic change of a population not of an individual. But all genetic change in a population comes about only through the procreation of new generations of individuals.
Evolution then is the result of the survival, success and reproduction of organisms within an environment which is changing. By environment I mean all surrounding factors whether geologic or climatic or of competition within the species or with other species. In a population of organisms the relative success of and subsequent reproduction of those better suited to the environment begets a gradual change in the characteristics of the surviving organisms. It is because of the environmental changes in the first place that there is a subsequent change in the characteristics of the organism best suited to that environment. It is this gradual change of the surviving characteristics that we call evolution and we say that the resultant, surviving characteristics have been “selected for”. If the environment did not change and if an organism was suited to its environment, the genetic make-up of the organisation would always tend back to its stable equilibrium position. Any mutational changes would provide no benefit and would just die away. Without environmental change there would be no evolution to report. Over long stretches of time and many thousands of generations, these gradual changes of environment have been sufficient to have created all the species of living things that have ever existed and to have eliminated all the non-viable species that have gone extinct.
There is therefore no naturally existing “force of evolution” or “force of natural selection” which causes change. It is environmental change (whether geologic change or climate change or the waxing and waning of intra-species or inter-species competition) which causes a shift in the characteristics needed to survive, succeed and reproduce. Then it is those individual organisms – among the existing population of organisms at any time – which have the most suitable characteristics which do survive, succeed and reproduce. It is their characteristics which we say have been “selected”. Natural selection is reactive and not pro-active. It does not select for environmental changes yet to come. It can cope with change only after the event and only to the extent that the natural variation of characteristics within a population are wide enough to include some individuals with characteristics suited to survival and reproduction after the change. If the environmental change is too fast or too drastic, the different characteristics available in a given population may not include any which can cope with the change. “Natural selection” then has not the capability to respond and a species becomes extinct. Every species which has ever gone extinct is an example of where evolution and natural selection have failed to cope.
Once upon a time – and not so very long ago – traits such as physical strength and height and speed and intelligence and resistance to disease all helped the survival of individuals and – more importantly – contributed directly to the procreation success of these individuals. Put simply, it was the strongest and tallest and fastest and brightest and healthiest among our ancestors who had the most children. The result was that their genetic traits were “selected for”. But in our modern society such genetic traits have been decoupled from survival and reproduction. Survival and reproductive success are no longer so dependent upon genetic traits. Height and speed and strength and intelligence provide no great advantage any longer in the procreation stakes. In today’s world medical science can compensate for many of these disadvantageous characteristics. Diet and drugs can help to make an individual stronger or faster when these traits are lacking and medical developments may improve his resistance to disease. Insofar as learning does have an influence on intelligence then any genetic disadvantages for intelligence can also be compensated for. But these corrections and compensations – these human interventions – which can improve the life of an individual are not – for the most part – inheritable.
Humans now routinely breed plants and animals selectively. “Artificial selection” is applied. Specific characteristics are sought and largely achieved by intervening – intentionally and with purpose – in the breeding and reproductive processes of these animals and plants. Without human intervention none of our current species of food crops would exist today. We would surely not have the various breeds of dogs and cats and cattle and sheep and pigs and horses we have today. Cloning is no longer science fiction. GM crops and animals are already here even if society has not quite come to grips with all their consequences.
Today children who – by virtue of their genetic characteristics – are born shorter or weaker or prone to disease or less intelligent than the norm are supported by medical science and the rest of society so that they can live full and satisfying lives. More significantly, they are not particularly disadvantaged when it comes to procreation and the passing on of their genes. The care of the “weak” in our midst – if they go on to procreate – must inevitably lead to their particular genes surviving and “weakening” the pool. So far as we know compassion or humanism are not genetic traits, but if they were, perhaps it would be those characteristics that would be strengthened in the pool. As I have posted earlier
If “intelligence” is an inherited characteristic – as it seems at least partially to be – then it is only a matter of simple arithmetic that unless the “more intelligent” reproduce at a higher rate than those of “less intelligence” then the “average intelligence” of the population will inevitably decrease.
There have only been isolated examples of the practice of eugenics – of humans trying to intentionally breed other humans. It has been largely discredited though it was a most respectable academic discipline in the 1920’s. Forced sterilisation in the name of eugenics was indeed practiced in many countries – and some of these programs only ended in the 1970’s. It may still be going on in Uzbekhistan. Genocide is still not extinct. In most societies today – with some exceptions – we no longer presume – usually – to impose on others as to which genetic characteristics are acceptable and which are not. To terminate a life or prevent an individual from procreating on the grounds of some genetic weakness would – in most societies today – be considered inhumane. But it could be argued that by encouraging termination of pregnancies for certain conditions we are actually beginning to go down that road. However, actively seeking specific genetic characteristics in future offspring does not carry as much stigma and is much more politically acceptable. To the extent of the knowledge we have, the practice of artificial insemination, surrogate motherhood and the selection by discerning ladies of desirable sperm from sperm banks for their offspring are nothing more than another facet of the practice of eugenics.
Today both “natural” selection and “artificial selection” are in play for humans but they operate at quite different speeds. “Natural “selection” applies universally but is slow. “Artificial selection” is much less common – as yet – but operates fast. The slow pace of natural selection which responds to and is in line with the gradual pace of geologic environmental change is now also overwhelmed by the pace of medical developments. Demographics tell us where the extra population which will take us from the 7 billion we are today to about 10 billion in 2100 will come from. About 1 billion from Asia and around 2 billion in Africa. But as development progresses their fertility rate will also decrease sharply and by 2100 the aging population of the world may be relatively stable. The composition of the world gene pool then will be a direct reflection of the composition of the 10 billion people in existence then and “natural selection” will hardly be evident in this time frame of 100 years.
The “artificial” selection of humans now takes two forms. Firstly the developments in medicine are now providing the possibility of procreation for some who may not otherwise have procreated. This allows the continuation of genetic traits which may not have otherwise continued. Second, there is a growing number of people who are intentionally trying to achieve specific genetic characteristics in their offspring; by selecting a sperm-partner for AI or by the selection of surrogate mothers or by the selection of specific sperm donors from sperm-banks.
But what all this means for the global “gene” pool in coming generations is not so clear. On the one hand some characteristics considered disadvantageous in the past no longer pose any significant disadvantage – for the individual. The disadvantage may have prevented the individual from successfully procreating in the past but no longer does so. The perceived genetic disadvantage – if truly a disadvantage – is passed on if the individual procreates. On the other hand we have one particular sperm donor who has been heavily selected by discerning ladies and may have fathered over 600 children! His genetic characteristics – for good or ill – are now over-represented in the future of coming generations.
“Natural selection” is very slow while “artificial selection” can be very fast. So any forecast of what the human gene pool may look like in coming generations is more likely to be effected by the rate at which “artificial selection” comes into play. I suspect that the most influential way this may impact the future is not so much by the joyless practice of AI or use of sperm banks but by being able to predict the propensity of a genome to disease. I suspect also that prediction of potential weakness in a genome will develop rather quickly but the repairing of such faulty genomes may still be a long way away. Whatever one may think about the morality of abortions, the early termination of “unwanted” pregnancies is here to stay. If genetic “faults” can be predicted at a very early stage then I am sure there will be an increased tendency to terminate fetuses which have such faults identified. So one development I foresee is that the incidence of those with “faulty genes” within the global gene pool will gradually reduce. The race will – I think – become much healthier with a lower propensity to disease. We will live longer but not because of a longevity gene but because we will be less prone to disease and infection. There will no doubt be much more mixing within the gene pool but I doubt – in the next few hundred years – that we will get noticeably much stronger or faster or taller – for genetic reasons. New Olympic records will continue to be set but they will be the result of better diet and improved training regimes rather than because of genetic characteristics. We may all well become much more knowledgeable about many, many things but we will probably not be much more intelligent than we are now. I do not expect either that we will have fewer bald people or more blue-eyed blondes.