Future human evolution will be selection by deselection

io9 carries  a look at how science fiction treats evolution :The most ludicrous depictions of evolution in science fiction history.

Of course this begs the question as to how humans are likely to evolve over the coming generations?

Humans and chimpanzees ancestors split some 7-8 million years ago and it took some 350,000 generations after that divergence for evolution by natural selection to produce anatomically modern humans (AMH). (This of course raises the question as to how chimpanzee evolution proceeded to reach modern chimpanzees while humans were developing into homo sapiens?).

It has been only about 10,000 generations since AMH appeared and only some 6,000 generations or so since modern humans left Africa. A very short time in evolutionary terms yet in this period humans have evolved to exhibit the various races of man that exist today. This differentiation is primarily superficial and all humans existing are capable of mating and producing viable offspring with each other. In theory humans existing today would also be compatible and – in the main – capable of mating with the humans of 6,000 generations ago. In practice a meeting of modern humans with those from 120,000 years ago would be an exaggerated replica of modern man meeting with isolated tribes in the 20th century. These isolated branches of humanity generally had lower levels of immunity to the bacteria carried by their distant cousins and were ravaged by disease after such encounters. The bacteria we carry are probably greatly different to those that humans carried at the dawn of anatomically modern humans. Probably no such meeting or mating would be very successful and one or both would probably succumb to disease brought on by the other’s bacteria. Nevertheless the genomes of the two – even after 6,000 generations – would  not be so very different and probably still be compatible. In any primate species a generational distance of over 20,000 between individuals will probably disqualify any theoretical possibility of successful mating.

The world is becoming a smaller place. As development progresses and living standards improve, fertility rates are changing and the advances in health care are increasing longevity. We modify our environments to be able to survive and procreate rather than environmental changes selecting naturally for those who can better survive and procreate. Selection of our descendants by human intervention is still small but increasing. We intervene in the selection of surviving individuals; mainly by caring for individuals who would otherwise not survive and reproduce but also by abortions of unwanted pregnancies, by IVF, by surrogate pregnancies and by selecting sperm from sperm banks. Taboos against mating and reproduction across racial boundaries are fading. The number of humans born (and prevented from being born) through human intervention is still relatively small but is increasing. Human selection – and particularly human deselection – is becoming more important to the result that we will call future evolution.

Fertlilty levels currently vary greatly across the world with the highest rates still in less developed regions. But as living standards across the world improve and converge, fertility rates are also reducing and converging. By 2100 fertility rates across the world will reach a level such that population will have stabilised and may even be decreasing slightly. The current variations of fertility across the world will influence the genetic composition of our descendants for only a relatively short time in evolutionary terms.

As instances of human selection and deselection increases relative to procreation entirely by natural selection what changes will humans undergo in the next 6,000 generations?

I suspect that the most profound influence will come from the deselection – before birth – of those genes known to cause failings of health. As the science of genetics identifies the characteristics which make humans more prone not only to life-threatening diseases but also to conditions which diminish the quality of life, humans will likely scan for and deselect (by abortion) such births. We can therefore expect – by this deselection alone – that longevity and the quality of the longer lifespan will increase. Selection by genetics for specific characteristics (height or intelligence or eye colour or strength for example) is likely to take much longer to become feasible and it is unlikely that humans will ever select specifically for just one characteristic. But humans might well come to select for some group of characteristics when – and if – they can be clearly identified.

Human selection and deselection – when used – will operate much faster than “natural selection”. The extent to which future evolution will depend upon human rather than natural selection will merely follow the growth of the use of human selection. It is likely that it is deselection of unwanted genes rather that the selection for specifically desired genes which will first come into play. I suspect that within the next 50 generations it will be common practice for foetuses with unwanted genes to be deselected. We shall be less susceptible to cancers and auto-immune diseases and obesity. Idiot savants will likely become extinct. We may become a little taller and a little more intelligent(?). If psychoses are genetic traits they may decrease. If we could we may well opt for enhancing our senses; better eyesight (better colour discrimination or better night vision) or better hearing. If we develop any new senses it will be by accident and not by design. If we could we may desire a more precise use of our memories or a greater speed of learning or a more efficient use of the intelligence we have. I suspect that “intelligence” itself is a composite result of many genes and is probably not something that we will be able to distinguish and select for for a very long time.

In the Year 102,013 I speculate that humans will:

  • have a lifespan of 400 years
  • be considered mature at age 50
  • have a “child bearing” period (male and female) from about 50 to about 250 years
  • be considered aged (and non-productive) at age 350 years
  • have an average height 5 cm taller than today
  • have an IQ on average some 30 points higher than today
  • consciously be able to erase certain long-term memories
  • see like a cat in the dark
  • be able to listen to the elephants rumble
  • be able to run 100 m in 6 seconds (as a record)
  • be able to run 50 km in 3 hours (as a record)
  • be able to jump over a bar at 3 m
  • leap distances of over 10 m in a single bound

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