The impact of genomics on the study of humankind’s history is both revolutionary and massive. Genomics history of humanity, as a separate scientific field, probably does not exist yet. Well, it is coming. It would be a rich, distinctive, and fast-developing area. Let us look briefly at the landscape of that field.
The Very Short List of Questions
Genomics could answer questions about what happened hundreds of thousands of years ago and about what happens now.
Here is a shortlist of topics where genomics could make a substantial input. Origins of humans. Interaction of different human species with each other. Population bottlenecks. Migration routes over the planet. The emergence of ethnic communities. Regional or global impact of individuals. The list goes on and on.
Let us touch on just a few points.
Genome Sequencing Is Not in Its Infancy Anymore
Scientists completed the Human Genome Project in 2003. In 2021 we could say that the genome sequencing procedure is routine.
The main focus is, of course, on genomes of us, Sapiens. Do you know how many people have had their genomes sequenced as of now? 30 million. At the same time, scientists have sequenced the complete genomes of more than 250 animal species. In 2018 the Earth BioGenome Project was launched. Its goal is “to sequence the DNA of the 1.5 million known species“.
The first works aimed to cover broad areas of the genomics history of humankind started to appear. Recent examples include “The Journey of Man: A Genetic Odyssey” book by Spencer Wells and “Global Picture of Genetic Relatedness and the Evolution of Humankind” article by a research team.
The Fascinating Story of Interbreeding
We know that Neanderthals, Denisovans, and Sapiens mated with each other. In other words, interbreeding between different species within the same genus Homo was common. The old criteria used to differentiate species by an inability to mate and produce healthy offspring are no longer valid for genus Homo.
Is it just happening with humans, who like the freedom of sleeping around so much? Or, is it shared with other genera too? And what are the consequences?
Jaguars and Lions vs Humans
The important discoveries came from recent articles about the Panthera genus, which consists of leopards, tigers, snow leopards, lions, and jaguars. The genomes of those big cats were sequenced in 2017 by a big team of researchers. One of this group’s leaders is Eduardo Eizirik, a biologist and ecologist at the Pontifical Catholic University of Rio Grande do Sul in Brazil. For many years he studied the jaguar. “Eizirik’s team found evidence of many crossings between the different Panthera species. In one case, two genes found in the jaguar pointed to a past hybridization with the lion.”
The interbreeding between species of the same genus is more frequent than previously thought. When even a small number of genes of different species are mixed, that is called hybridization. When one species inherits genes from another, the outcome can be either damaging, neutral, or adaptive. In the jaguar case, the lion’s genes involved in optic nerve formation took the place of those the jaguar initially had.
As Michael Arnold, an evolutionary biologist at the University of Georgia, said, “Diversification, adaptation, and adaptive evolution do seem to be driven quite often by genes moving around.”
There are many examples of “genes moving around” between Sapiens, Neanderthals, Denisovans, and some other human species. It is also important to note that this kind of hybridization introduces another channel of the genetic variation in addition to within-the-same-species mating.
The other thing is that leopards, tigers, snow leopards, lions, and jaguars have many shared genes. With interbreeding between different species of the same genus, those common genes could add to the genetic variation even without hybridization.
Mitochondrial Eve and Origins of Sapiens
There are a lot of questions about humans and, in particular, Sapiens origins. One such question is about the most common ancestors, male and female, for Homo Sapiens.
It is assumed that all humans have a common theoretical ancestor on a maternal line. This woman is known as “mitochondrial Eve.” So far, all sequenced Sapiens genomes point to such “mitochondrial Eve.” The late research shows that “mitochondrial Eve” probably, lived between 100,000 and 200,000 years ago in southern Africa.
The existence of “mitochondrial Eve” tells us that every other female lineage eventually had no female offspring. How could that happen?
“Founder Effect” in Human History
One possible explanation is that at some point a long time ago, Homo Sapien’s history was shaped by severe population bottlenecks or the so-called “founder effect.” Both are examples of genetic drift when some genes from a population are eliminated.
“When a small group separates from a larger population and strikes out on its own, that small group might be carrying genes that are rare in the original population. These rare genes will now be common among the new group’s descendants. However, other genes present in the original population may be absent from the new group altogether.” That is the founder effect.
In our two-million-years history, humans migrated from Africa and further on Earth many times. During migrations, typically, just a small group of the current population migrates and sets up a new colony. There is no doubt that founder effects were encountered by humans. Yet, to scientifically prove when and where population bottleneck or founder effects happen with humans is not a small feat.
In a Search for mitochondrial Eve
Here is an example of a founder effect, which was confirmed by genomics. “The Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease.”
So far, there is no similar confirmation for population bottleneck or founder effect at the times of mitochondrial Eve. However, the Sapiens jawbone was found in Misliya Cave on Mount Carmel in Israel. Dating techniques suggest the jawbone is between 175,000-200,000 years old. That discovery points to Sapiens migration from Africa. That time is close to the time of mitochondrial Eve’s existence.
It is exciting to look at humankind’s history through genomics lenses. We may be back to genomics later on. Go to Comments on this blog post.
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