Your Life as Planet Earth

A new way to understand the story of the Earth, its climate and our origins

Human evolution is dead. Long live Human evolution.

This is a 1500 word essay I wrote for assessment in the excellent Human Evolution MOOC by John Hawks

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For the most part everyone who is born these days will get the chance to have kids of their own. Medicine has made us all equally “fit,” (in the evolutionary meaning of the word) so that we can all, with ever-fewer exceptions, have babies. For humans living in the modern era there is no longer the survival of the fittest, no longer any natural selection.

Human evolution seems dead. But is it really?

Evolution is genetic change inherited by subsequent generations. But it happens through a variety of mechanisms, not just natural selection. These mechanisms include sex (shuffling of genes by sexual reproduction), germ-line mutations (genetic ‘errors’ in eggs and sperm), genetic drift (random change in genetic makeup of a population over time), gene flow (interbreeding of genetically-different populations), and finally selection (non-random change in genetic makeup of succeeding generations). Even coevolution (two species evolving an interdependence over time) may become relevant. We must look deeper into each of those processes to see if they no longer work before we can cast judgment on whether human evolution is dead.

When mankind first set foot on the Moon in 1969, a pop song called: "In the Year 2525," composed by Rick Evans, captured the future-gazing mood. I’ll use that song’s milestones to speculate on how humans may or may not evolve into the future.

Now: Gene flow

We are currently in a genetic blender. “Melting pot” doesn't do justice to the breadth and thoroughness of the flow of genes throughout the human species today. In 2013 the number of international migrants reached 232 million (over 3% of the global population) and looks set to increase.

My own children carry the genetic heritage of two different continents in just one generation, and in that time our family has migrated across four continents. Geography is no longer an effective barrier to interbreeding between populations.

This means that genetic traits formerly concentrated in isolated populations will become homogenized across the entire human race in a few generations. Will we be able to tell “races” apart in a few generations? Hopefully not.

The year 2525: Genetic drift

By the year 2525 (around 20 generations) the gene flow of today will have resulted in a largely genetically-homogeneous human race. But what will humans look like?

By chance some people have more descendants than others. But at the gene level it’s a numbers game, with the largest breeding populations inevitably having the largest statistical chance to impose their genes on subsequent generations, and contributing most mutations to the genome. So we need to look at where the most babies are being born, and where those babies are surviving long enough to have their own babies, to see how the genetic mix of humans will be skewed in 5 centuries’ time.

According to the United Nations, by the year 2100 some 24 countries are projected to have populations of over 1 billion. It is striking that half of those are Sub-Saharan African countries, with South Asia and East Asia representing most of the rest. With the exception of Russia, there are no European countries in this list. It’s hard to escape the conclusion that by the year 2525 a homogenized human population will be genetically most like a mixture of Sub-Saharan-African, East and South Asian, with a small element of Latino (from Brazil and the USA).

The year 3535: Selection

In the introduction we assumed that selection is dead in the era of modern medicine. But is it? Will population growth alone drive the prevalence of genes in the human population by the year 3535 (around 60 generations)?

Between 2100 and 3535 global warming will have wreaked havoc on society. Sea levels may have risen by 50 meters (160 feet), drowning the coastal cities of today. Heat waves and drought and water shortage will have rendered large tropical areas unpleasant to uninhabitable. Ocean acidification will have caused a collapse in fisheries sustaining large sections of population, perhaps hitting East Asian island populations hardest. Agricultural production will have shifted in favor of nations like Canada and Russia, and be less productive than today, resulting in frequent famines.

This will exercise natural selection against the most affected populations, and this would be stacked against the very Sub-Saharan and South Asian populations which genetic drift would seem to favor. It's hard to imagine evolution via sexual selection, given that everyone can find their match through online dating today.

But not all selection is natural. It seems likely that gene therapy on germ-line cells, and artificial selection of embryos, will have eliminated most inherited diseases like hemophilia and other afflictions with a genetic element like cancers, obesity and diabetes, at least in rich countries.

But why stop at diseases?

The year 4545: Germ-line mutations

By the year 4545 (around 85 generations), if not earlier, it seems likely that technology will allow the error-checking of embryonic genetic makeup, and automated correction of any random mutations.

In contrast, by the year 4545, deliberate heritable mutations to engineer desirable traits will likely dominate (making humans Genetically Modified Organisms - GMOs). Designer-babies, so ethically abhorrent today, will inevitably be widespread, trending towards a standardized basket of beauty and other desirable traits. The question will just be: who has access to them? Will they be the exclusive preserve of rogue nations? The rich? Or will they be considered a “right” for all with access to health care? We will strive for these traits, acquiring them like property or trust funds to bequeath to our descendants. But if we all converge on a similar genetic pattern, we will become more vulnerable to pandemics. It seems possible that regulatory pressures to maintain a certain level of genetic variability will compete with commercial pressures to have the latest and greatest genes.

The year 5555: Coevolution and speciation

Today human heritable genetic code contains genes for non-human species called “endogenous retroviruses.” Viruses are generally considered life forms, even though they can only reproduce using other organisms.

It could be argued that the 21st century witnessed the beginning of a new virus-like entity, with which by the year 5555 (around 120 generations into the future) we will have co-evolved, forming a mutually dependent symbiosis. That new virus-like entity is Personal Technology (cell phones, iPads, etc), which reproduces only with the aid of humans, and yet we are increasingly dependent on it.

About 2.7 billion years ago, two domains of life merged to create a third – eukaryotes  - a chimera that gave rise to fungi, plants and animals – including us. It happened again 1.8 billion years ago to produce the earliest plants.

By 5555 humans may not only have adapted technology to our needs, but we will have adapted ourselves to it. A seamless link between our bodies and technology, and therefore our brains and everyone else’s, will probably be commonplace. Is Facebook an early sign of a future hive intelligence? Perhaps the mutation-correcting technology envisaged by the year 4545 will by now be inherited, endogenous, organic nanotechnology, constructed from our own genetic code. Perhaps our technological-neural interfaces will be programmed into our genes, using DNA computing, so that we will be born in symbiosis with Personal Technology.

We will have co-evolved with technology into a chimera organism, and it will be impossible for those new chimeras to reproduce with the humans of today. By definition therefore, this new organism will be a new species, arguably even a new domain of life.

The year 9595: “Now it's been ten thousand years, man has cried a billion tears”

Ten thousand years. It sounds impossibly far into the future, with endless opportunities and uncertainties. But look in the other direction – back to the past. 10,000 years is just 0.5% of the time since the appearance of Homo erectus, our first fire-making, food-cooking, big-game-hunting intercontinental ancestor. If we evolved from erectus in 1.8 million years through the chance effects of mutation, genetic drift, gene flow and natural selection, think how much faster evolution must inevitably occur in the next 10,000 years not just by chance but also by population growth, mass migration, applying knowledge, technology, and deliberate selection.

It is already starting. Mass international migration and interbreeding is causing a profound genetic shuffling by gene flow. Population growth is increasing the frequencies of mutations and the prevalence sub-Saharan African, South and East Asian genes. Climate change will reduce the reproduction chances of people in the most affected regions, even as rich countries adopt positive artificial selection for desirable traits. Random mutations will be “corrected” by gene therapy even as deliberate human mutations become the most important inherited mutations. Eventually, coevolution with Personal Technology may turn us into a new chimera species, arguably representing a new domain of life, unable to reproduce with the humans of today.

Human evolution is far from dead, in fact we are just catching the first dawn rays of its greatest leap since the emergence of Homo erectus 1.8 million years ago.

 

John Hawks has an article on our recent and ongoing evolution in Scientific American titled: No, Humans Have Not Stopped Evolving