Have humans finally stopped natural selection? What’s in store for us now?
What is Evolution?
What came first – the chicken or the egg? People who say chicken or think there is no real answer simply don’t understand the concept of evolution.
Let’s start with the basics. The neo-Darwinian definition of evolution is the change in allele frequency over generations. But what are alleles? An allele (pronounce it how you like, everybody does) is a form of a gene. For example, imagine there is a single gene which determines hair colour. One allele would result in brown hair, another allele would confer blonde hair, while the third allele could produce red hair. They are all just different forms of the same gene.
What Affects Evolution?
The major forces that influence evolution are mutation, natural selection, genetic drift and migration. Mutation introduces new variants providing fresh material for evolution. Other forces affect the allele frequencies in the populations either deterministically, like natural selection and migration, or stochastically, like drift.
So as for chicken versus egg, it must have been the egg which came first. The egg had to contain the mutations that gave rise to the chicken. Whatever laid the egg was not itself a chicken, but a chicken-like creature that laid eggs. Natural selection allowed this new mutated species to survive and propagate.
Crash Course in Natural Selection
The theory of natural selection rests on three observations:
- Population size would increase without limit if all individuals born survived. Since no population can grow without bound, not all will survive. This is known as reproductive excess.
- Individuals differ in their chances of survival and reproduction.
- Such differences in fitness are heritable.
And lo, Darwin’s theory of natural selection was born! Evolution is then inevitable. In essence, natural selection is survival of the fittest and prettiest; genes which confer increased chances of survival and reproduction earn passage to subsequent generations. This is because individuals who possess certain alleles which are better adapted to their environment and have better chances of reproduction contribute more to the next generation. In animal populations this holds, but I believe some human populations have changed course.
Mankind has stopped evolving after becoming the only species to “put a halt to natural selection of its own free will” as David Attenborough famously put it. Natural selection is survival of the fittest and sexiest but we now have means to keep the weakest alive and the grotesque a rockin’. We are able to rear around 99% of all babies born to adulthood. This alone refutes the first two principles of natural selection.
Instead, I believe humans will continue to evolve in a cultural sense through knowledge, technology and medicine.
Genes are becoming less of a factor in human evolution. If a disease arises, we devise medicine to treat it. If we need to travel further we invent transport to take us there. If we want to look prettier we seek cosmetic improvement. If we need to be smarter we develop technology to think harder for us. We don’t need to evolve to outwit any predators; we are the ultimate predator. There is now less pressure for our genes to adapt to a changing environment. Instead, we use technology and medicine to increase our chances of survival so our genes don’t have to!
However, people develop technology and medicine. Better people develop better technology. Certain genotypes are sometimes associated with higher intelligence. So perhaps the evolutionary pressure is developing smarter people rather than more disease resistant, stronger or sexier individuals. You could argue that evolution of genes which confer greater intellect drives the technological evolution of mankind.
To say genetic evolution has been phased out entirely would be brash. For instance, there may be no evolutionary pressure to outwit a predator. But the human race falls victim to intraspecific predation – physically and more recently, financially. While physical survival is less of an evolutionary pressure in the developed world, financial survival certainly is. Sharp minds with the ability to accumulate wealth tend to have more children and a better chance at survival. So, intellect and cunning could still be being driven by natural selection.
Stagnation of evolution is only really true in the developed world where it is suppressed by knowledge and technology. It is easy to conceive of a future Africa populated by the descendants of a few HIV-immune people. We have seen this happen already with Chimpanzees. Many carry the AIDS virus but are unaffected by it because they carry genes which confer immunity. These Chimpanzees are descendants from a few thousand-year old ancestors who were immune to HIV.
It’s easy to think that humans have stopped evolving. But I think human evolution just works differently to days of old. Modern day is a good time to be alive. With almost 99% of all born making it past 25, future society may look back to a less crowded and healthier world. In the future, the human race may drive its own evolution by bio-engineering people using gene manipulation to create a superclass of Captain Americas. A unsettling and believable prospect.
Master of Human Genetics
from University College London