by James Morris
In light of recent events, I think it’s important to remind ourselves how similar we are to each other, not how different.
If you look at your family tree, you first come to close relatives, then distant ones. Ancestry companies using the latest DNA technology can help you find relatives you didn’t even know you had or uncover branches of your family tree long forgotten.
If you continue to zoom out, you eventually come to the human family tree, including everyone alive today and your human ancestors.
How closely related are you to everyone else? You are about 99.9% genetically identical to all other people, or 0.1% different. This is a very small difference.
Our species is only about 200,000 – 300,000 years old. In this short period, there simply has not been very much time for us to become very genetically different from one person to the next. We are a young species, with relatively little genetic variation among different individuals.
This may come as a surprise because, if you look around, one of the first things you notice are human differences, not similarities. You might notice that hair color or texture varies quite a bit among people. Or eye color, nose shape, skin color, height, or weight.
We are particularly good at noticing differences among one another. In fact, we have grouped these differences into discrete categories called races. These races place people into just a handful of separate, non-overlapping groups based on outward appearances. And then we sometimes connect these superficial differences with much deeper ones, such as intellectual or athletic ability.
The racial categorization of humans, however, has no basis in biology. It is a social construct, used sometimes as a statement of identity, belonging, and pride, and sometimes to categorize, separate, and control people.
From a genetic perspective, we are simply not that different from each other. Many species, even ones whose members look quite similar to one another like fruit flies, harbor much more genetic diversity than we do. What this means is that external differences do not correlate well with underlying genetic differences.
In addition, there is actually no single trait (like a particular skin color or nose shape) that is universally present in one so-called race, but completely absent in another. In other words, it is impossible to come up with a trait that every member of one race has and that no one in another race has.
Finally, if we look at the amount of genetic variation within any race and compare it to the amount of genetic variation between any two races, we find something unexpected: there is much more genetic variation within a race than between two races. Put another way, there is more genetic variation within a group like Africans or Europeans, than there is between Africans and Europeans.
This doesn’t mean that “race” is not real. Race, as a social and historical concept, is certainly real and has very real effects. Racial disparities in health and economics, for example, are tangible effects of living in a racialized society.
This also doesn’t mean that there are no genetic differences among human groups. Some differences, like skin color, seem to be adaptive: ultraviolet radiation is necessary for vitamin D synthesis but can also cause damage, so skin color varies depending on the intensity of sunlight. Other traits, like eye and nose shape, may be sexually selected, as first proposed by Charles Darwin. There are also particular diseases (like Tay-Sachs) that are only found in some populations. However, these traits result from a very small amount of genetic difference and they don’t map on traditional racial categories.
The obvious physical differences are literally just skin deep. The same is true in other organisms. For example, peaches have fuzzy skin and nectarines have smooth skin. This dramatic external change is the result of a single change (mutation) in one gene. Peaches and nectarines are essentially the same fruit with different skins.
The various qualities that make us human – our thought, intelligence, athleticism, musical ability, language, and so on – are universal human traits.
We can learn even more about ourselves by looking at our recent evolutionary past. Our closest living relative is the chimpanzee. Humans and chimpanzees share a common ancestor that lived about 6-7 million years ago.
We have a lot in common with chimpanzees, but also a host of differences. Those differences evolved during the time we have been separated from chimpanzees. These include our big brains, allowing for tool use, language, and culture; opposable thumbs; ability to walk upright; and long childhood, allowing us to explore, learn, and play over an extended period of time.
One way we can trace these changes is to look at human-like fossils younger than 6 million years. Two particularly famous fossils are Lucy and Ardi. Lucy was discovered in 1974 in Ethiopia and is about 3.2 million years old. Ardi is older than Lucy, about 4.4 million years old, but is a more complete fossil. She was discovered in 1994, also in Ethiopia. Both are hominins – early human ancestors.
Lucy and Ardi lived in Africa. Since the split with chimpanzees, there were several migrations of hominins out of Africa to the rest of the world. Some of our human ancestors leaving Africa came across another hominin group known as Neanderthals. Neanderthals, with their heavy brow and stocky frame, have entered popular culture with sayings like, “Don’t be such a Neanderthal.”
The Neanderthals lived in many of the same places and at the same time as the line that led to modern humans. Furthermore, there now is clear evidence of interbreeding between the two groups. It is estimated that 1-4% of the DNA of many of us is Neanderthal and responsible for some of our traits, such as our ability to fight certain infections, but also a predilection for certain diseases.
Tracing our evolutionary history allows us to come back to the question of how we are all related. Humans have very little genetic variation, and now we can say that, of this little amount, most of it can be found in Africa. This is because the groups of early humans that left Africa only carried with them a subset of the genetic variation present in the original African population.
In addition, because early humans encountered Neanderthals outside of Africa, only descendants of these early travelers, like modern Europeans, carry Neanderthal DNA. Africans don’t because their ancestors didn’t interbreed with Neanderthals.
The history of our species is one of repeated episodes of migration, mating, and mixing. As a result, just as there are no pure “races,” there are also no pure “groups,” such as British, French, or Germans. The only groups that might be able to claim a long history with relatively little intermixing are some Canadian and Alaskan Native American tribes and Australian Aborigines.
Like any family, the human family has a messy and complicated history, but it helps us to understand that, in the words of Maya Angelou, “We are more alike, my friends, than we are unalike.”
© James Morris and Science Whys, 2017