Future Humans — Selected Topics
I think that it is time to plug my Future Humans book once more. So I thought I would list a few of the topics it covers, accompanied with some quotes.
On the question of whether evolution has stopped as a consequence of new technology and medicine:
If we ignore selection, alleles will still get fixed randomly, and new mutations will still enter the population. Unless we can stop mutations entirely — which seems incredibly unlikely — or humanity goes extinct, this process will always continue. The composition of alleles in the species will slowly change as some variants increase in frequency, and others decrease. Some mutations will be lost, but new ones will continually show up to replace them. The high rate of mutations ensures that we will always have the same alleles in the population, but this does not imply that the population never changes. It is the combination of alleles in many genes that determine what we are, and a rare variant here and there does not change the vast collections of common combinations in the species. With this random process of shifting allele frequencies alone, we will slowly and aimlessly drift until we would be considered a new species. Even with no selection, we would still evolve. Just very slowly. With selection, our evolution will progress considerably faster.
For selection to matter, we must have something to select for. If no new mutation provides us with a substantial selective advantage, then we only have the slow random genetic drift to change our genomes. But are we at perfect fitness, from where no improvements are possible? Hardly. For one thing, consider diseases that are partially genetically caused. We know many alleles that increase the risk of various diseases, some substantially and some slightly. Unless there are selective reasons to keep these alleles around — which there might be since genes can have more than one function — evolution should be able to get rid of them.
With modern technology, we no longer need to outrun predators — at least most people don’t. We protect and feed those that cannot do so themselves. Modern medicine alleviates the impact of infectious diseases, something that has been a considerable driver of adaptation. We are not at the point where infections are harmless, the COVID-19 pandemic testifies to that, but infections are far less likely to kill us today than in the past. We have removed many of the drivers that guided selection before, and for those areas of the Earth where these modern advances are still not widely available, they soon will be. While new technologies are not evenly distributed, they spread through all populations, eventually, if the economic and technological trend that humanity is currently on continues.
If these selective forces are gone, we can then ask ourselves if there is still an opportunity for adaptation? These environmental factors might no longer require (or enable) selection. I have often been asked if evolution has stopped because our environment is no longer as hostile to us. In the world today, we have eliminated many of the dangers of the past, but the changes that removed the old selective pressures were changes to our environment. We now find ourselves in a world we didn’t evolve in. We are not adapted to the modern world; there hasn’t been enough time. The traits that evolution will select for in the future are different from the traits it selected for in the past, but there will still be selection.
Spoiler alert: we will, if anything, evolve faster in the future than we did in the past.
On ageing:
Our species evolved in small societies with high birth rates and high mortality rates. Most of the human population were children or teens, and few were old. Soon, the entire world will have transitioned to a world where a significant fraction of the population is old. At the global level, the estimate for 2050 is that 22% of the human population is older than 60. Already today, in seven countries, more than 20% of the population is older than 65; in order of percentages: Japan, Italy, Germany, Portugal, Finland, Bulgaria, and Greece. For Japan, the most aged population, more than one out of four, 27%, are older than 65, and Italy is not far behind with 23%. This is a dramatic change to our species, and it will affect our future evolution. When most of the population was young, genes that were helpful at a young age were strongly selected for. There will be genes that are beneficial at advanced ages, but in our past, few survived to benefit from them. The fraction of the population at an advanced age was small, and the selection wasn’t particularly effective for the genes that matter there. Now, this has changed.
From a life expectancy below 30 in the Stone, Bronze, and Iron Age, we now have a life expectancy in the seventies and eighties in the developed world (and the developing world is not lagging far behind). Most of the increase in life expectancy is the decrease in child mortality, which strongly influences the mean life expectancy. Even in the past, it was common to live decades beyond the mean if you made it as far as the mean; the low life expectancy was a result of only a few children surviving beyond childhood. But even if we ignore the effect that child mortality has on the past versus current life expectancy, we are getting older. If you stratify by age, you see an increase in life expectancy for all age groups. We keep people alive well beyond reproductive age. Could some genes affect our bodies in our seventies, eighties, and nineties with alleles that were never before seen by selection? Can these be selected for if we live longer? The answer depends, of course, on how these genes affect reproductive success, either for ourselves or for our offspring.
I think that there are many interesting possible consequences of an ageing population. One interesting aspect could be sexual selection:
When young males get into fights, we see a touch of sexual selection. Their potential mate sees that they are ready to fight to protect them. But there is also another aspect to it. Fighting over access to mates is common in the animal kingdom, and we do it as well. It has served us well in the past; we are the product of genes from males that could fight off other males. Today, as a general rule, we don’t have to fight with other males to mate, it is generally self-destructive behavior, but we still have the tendencies, because we evolved that way.
We usually grow out of this behavior, although some more than others. There are still those that are looking for a fight at age 50, but as a rule, you are more likely to get into a fight when you are 20 than when you are 50. As a society, we do not condone destructive behavior for those in the twenties, but we expect it to some degree. We are not as forgiving about destructive behavior from middle-aged people, because we expect them to have grown up and gotten smarter about it.
We have different behavior in different stages of our lives because selection needs us to do different things. When we are looking for a mate when we are young, we need to show off our genes. Once we have started a family, we need to protect our offspring. We can take risks to find a mate because we do not have much to lose. It is either finding a mate or not reproducing, so whatever it takes to look attractive is worth it. Once we have offspring, taking risks puts us at a selective disadvantage. If we die, we cannot protect and provide for our children. What we find attractive also reflects this. We are not, generally speaking, looking for cowardly genes in our youth, and we do not want reckless behavior in a spouse.
We start with the self-destructive behavior at a younger age than we reproduce today, but around the time that we are biologically able to. We usually stop the behavior before we settle down and start a family. Our reproductive behavior is slightly out of sync with the behavior we use to attract mates. At the age that we actually reproduce, rather than when we potentially could, we are attracted to different traits than those we evolved to display. If you keep behaving in your late twenties as you did in your teens, your fitness will be lower. Mates do not find it attractive. You have to grow up or leave the gene pool. If we start reproducing in our forties or fifties, teen-like behavior will put you at an even greater fitness disadvantage.
Stranger still, with failing sperm quality at more advanced age combined with increased pollution that affects fertility, could we see selection for being sperm donors? Maybe…
In vitro fertilization, or IVF, is our technological approach to alleviating the consequence of our own pollution, and it can compensate for low sperm quality. If the quality is too low, however, it doesn’t suffice unless we add a sperm donor to the equation. Donated sperm must come from a donor with sufficiently high sperm quality, so now we have added an additional source of selection to alleles that add resistance to hormonal pollution. If there are genetic components to the willingness to become a sperm donor — there might be, although I have never seen a study that examines it — then we would also see a strong selection for these. In either case, while alleles that reduce sperm quality are selected strongly against, the alleles that come through sperm donors will have a strong positive selection. Different countries have laws that limit the number of children that a single donor can be the father of, but international trade of sperm bypass these laws, and a single donor can be the father to vastly more children than he would normally be able to without sperm donation. Sperm donation and variation in fertility give us such a steep selective gradient that we can see an adaptive effect even if the exposure to pollution is temporary.
Reproduce through sperm donation gives you a huge selective advantage. You have no of the obligations, you are in effect mating with potentially tens or hundreds, and your genes could quickly outcompete your rivals.
Speaking of sperm donation, that could be the first steps towards a eugenic future, but for that argument you have to read the book.
I don’t think we will be guided by random natural selection much longer. We will soon switch to artificial selection, where we explicitly choose which genes the next generation should have.
Many will object that we should not screen for traits and select children based on the result, but nevertheless, it happens every day. When parents have the choice between a child with a genetic disease or to wait for one without, many naturally choose to wait and try again. It is easy to have a moral stand on the abstract scenario, but when it comes to your own children, you want what is best for them. You want them to be healthy and able to live a good life. You do not wish to bring into this world a child you know will live, perhaps, a short life in constant pain. I would go so far to say that I find it immoral to do so if you can avoid it. To me, avoiding unnecessary pain is a morally superior choice.
From screening, it is a short step to active manipulation
If we select for traits based on screening, we only have the variation already in the parents to work with. The embryo will be a combination of these (plus a tiny number of mutations), and we cannot pick and mix genes from the entire human species. This is a limitation we can get rid of if we explicitly modify genes instead of selecting them based on screening.
Modifying genes might sound like science fiction as well, but it isn’t. The first genetically modified children are already born. The first, a pair of twins, was born in November 2018. They were modified to increase their resistance to HIV. The doctor doing the gene-editing was sentenced to jail afterward, and rightly so — no one knows what the consequences of this editing are, and we need to know the ramifications of our actions before we experiment on humans. However, the technique used to do this, called CRISPR, is used in labs all over the world, and nothing except ethics committees and legislation prevent others from modifying embryos.
Of course, our future might not be biological at all. We could end up building machines that will replace us.
You might think this is a bleak view on humanity’s future, but think about it this way: they are our children, albeit in a different medium. If we manage to endow them with the goals, dreams, and qualities that we possess, why should we think of them as much different from our biological offspring? It won’t be genetic offspring, but if you hope that your genes will continue down the ages, I am sorry to tell you that the chances are slim. Each generation, some of the genes you have contributed to the human gene pool are likely to be lost. The chance that a particular allele you carry will survive to spread through the species is the same as the chance that a new mutation will survive. Think of your specific allele as the mutation and consider its probability of getting fixed in the population. Earlier in the book, we calculated this probability to be one in 14 billion — although that chance depends on the number of people in each generation. If the human population size stays at seven billion, this is the result we get. If the population size grows, which I expect it to do over a million years if we expand into space, then the chance is much smaller.
Some of your genes might spread to all of humanity in the future if the allele copies you carry get fixed. The chances are tiny, though; you are competing against all of humanity in this lottery. All genes that do not replace the rest of humanity’s copies will be lost. Even those distant descendants that can trace their pedigree back to you will likely not carry any of your genes; they also got their genes from their other ancestors, and the contribution from all of humanity swamps your contribution. You will have contributed the same number of genes to the future biological humanity as you have contributed to the artificial intelligence humanity.
This, and much more, is in the book. I think you should buy it, but I am, admittedly, slightly biased.
