Genomics, a science that deals with DNA mutations, provides an answer.
On June 8, geneticist and anthropologist Spencer Wells visited Strelka with a lecture entitled, “ DNA Storytelling: A Genetic Odyssey”. What can DNA-testing tell us about human history, what demographic trends will mark the 21st century, and how is genomics becoming a business: these were some of the questions that Wells addressed in Strelka’s courtyard. Biologist and science journalist Alexey Torgashev explains why Wells’s research should be of interest to everyone, from schoolchildren to designers and sociologists.
I’d like to come out: I’m a mutant. But you shouldn’t judge me; we share the same problems. Chernobyl, ozone holes, or supermarket food have nothing to do with it. It’s not the fault of your parents or American imperialism, either. It’s just the way nature works: when we are born each of us get our own share of mutations: not too many, around a hundred per genome. And even though radiation and poisonous chemicals undoubtedly speed up this process, it develops even without the help of mutagens.
Why? Because genetic information is stored in the DNA, long molecules that consist of nucleobases. Geneticists refer to them as A, T, G, and C. Various combinations of these letters form chains. As a result, a record containing information on the functioning of the organism is produced. If we replace even one thing, this text will change. This is what we call a mutation. But how do these changes occur? Almost every molecule contains a full set of DNA, and when a cell begins reproduction, this DNA can be copied. So then each of the two new cells gets its own set of genes. This is always the case with cell duplication: molecular machines are constantly rewriting combinations into their new copies. And sometimes they make errors. The text, by the way, is quite long: 6 billion letters. So 100 errors is actually not that bad. If any of us decided to rewrite “War and Peace”, the result would be much worse.
When mutations end up in the egg and sperm cells, they are passed on from one generation to the next. That’s why we are mutants, and our parents were mutants, too. But no need to despair; without mutations, there’s no evolution. Natural selection chooses positive changes and discards malicious ones.
However, most mutations are not just harmless, they are also useless. There’s a lot of gobbledegook present in-between the more sensible fragments of the DNA record. Adding a comma or a new paragraph of text will produce no effect on the organism. Even within the genes themselves, there are areas where replacing a letter would make absolutely no difference. These neutral mutations are not affected by natural selection, they just pass from one descendant to another, gradually accumulating in the genome. The evolutionary clock is ticking with roughly the same rhythm: in one of the offspring, the A is replaced with a T, boom; a different replacement occurs in another one. In human evolution, this goes on for hundreds of thousands of years. By comparing the DNA records, we can find out when and how homo sapiens started to spread across the world after starting its journey in Africa.
That’s how we do it: we collect DNA samples from as many people living today as possible. Analyse their mutations. Note the differences. Find the most common mutations. These ones are the earliest. Then, we search for a common mutation within a specific group; for example, the Europids. It will not be the same for the Asian group. If we know how long it takes for a mutation to spread, we can establish when humans emerged in one region or another. Then we can compare this to the archaeological findings...
This science has been rapidly evolving since the 1970s, when the first methods for de-coding DNA records were developed: expensive and time-consuming, but effective. A molecular-based time-telescope appeared. By the 2000s, it was established that all men on Earth are descendants of the “Y-chromosome Adam”, who lived in Africa (it was initially supposed that he wandered the savannah 60,000 years ago, but new estimates have moved this to 200-300 thousand years). Another conclusion was that all people have in their DNA a fragment of a “mitochondrial Eve”, although altered by mutations. At a later stage, researchers discovered the “Adams” and the “Eves” of each race and arrived at the conclusion that humans travelled from Africa to Asia, then to Australia, afterwards to Europe, and only then to both of the Americas. Their routes were traced, and in some cases even the average number of migrants was established.
The 21st century saw the completion of the lengthy and expensive Human Genome Project, a dramatic increase in the quality of angular resolution in the molecular research methods; the tests themselves are becoming cheaper each year — for roughly $1000 anyone can get a personalised DNA analysis today.
A man called Spencer Welles spent 10 years as head of the biggest research project on human ancestry, the Genographic Project. Almost a million DNA samples were collected from people living in different parts of the world. This proved to be a timely enterprise. In order to establish where our ancestors come from, it was necessary to collect DNA from descendants who had been living in the same area for a lengthy period of time in relative isolation from neighbouring populations. Which means primarily indigenous peoples and traditional communities. Today, these groups are rapidly vanishing as the world is becoming one big global village: an average person in any given megalopolis carries DNA mutations from all over the world. Anyone can trace their origins simply by spitting into a test-tube. The test will show which parts of your genome came from Hungarians, which from the Chinese, and which from the neanderthals. By the way, the latter is a recently developed technology and an absolute miracle: the neanderthal genome was first decoded in 2009 (the DNA was extracted from the bones) and it turned out that 1-4% of our DNA comes from the crossbreeding of our ancestors with neanderthals.
Also: earlier I mentioned that every man on Earth is a descendant of the “Y chromosome Adam” and every woman of a “methochodric Eve”. This is not exactly correct.
There are two reasons for this. Firstly, because we receive chromosomes from both our father and our mother, and due to the fact that chromosomes themselves share fragments during duplication, we end up receiving particles from many other people who lived before us. Only the Y-chromosome and the mitochondrial genome do not perform this exchange. But they contain only an insignificant number of important genes; it’s their resistance to intermingling that lead them to being used by scientists for tracing evolution. Genes from the other chromosomes came from many different men and women who were wandering the African continent together with Adam and Eve. Neanderthal DNA proved exactly that: we are all descendants of various kinds of humans, some of them grandfathers and grandmothers of non-homo sapiens species.
Secondly, in order to establish that we all possess a piece of that particular Adam or that particular Eve, we would have to check every single person on Earth. How can we be sure that there isn’t someone somewhere with a Y-chromosome of a neanderthal man and a mitochondrial DNA of a neanderthal woman. Why not?
By comparing the DNA of many different organisms, not just humans, we can find out a lot about what life was like in the past. A very young science called “genomics” is dedicated to this. It used to be impossible to practice it because of underdeveloped computers and expensive DNA decoding methods. But the recent discoveries of this 20-year old science are very impressive: recently, researchers managed to find an organism called LUCA, the Last Universal Common Ancestor. Of course, LUCA doesn’t exist anymore: it provided us with a beginning and vanished over 3 billion years ago. But we know which genes it contained. And we are all its descendants.
P. S. Modern genomics can tell us not only about our ancestors, but also about our descendants and about the challenges of our life as we live it today. A DNA test shows which illnesses you and your children are more likely to inherit. Other branches of molecular biology are working on improving humans: two years ago, Chinese scientists attempted the first experimental editing of the human embryo genome in order to fix a malicious mutation. And this is just the beginning. In just a couple of years, we will be able to choose the characteristics of our future children. And who wouldn’t want that?
Text: Andrey Torgashev
Translation: Alexandra Tumarkina