Homo sapiens are one species. There are no subspecies of humans, and our last relatives in the genus Homo went extinct around 40,000 years ago. But what explains how similar we humans are to each other? And more importantly, what genetic variants make different human populations and individuals so unique?
Some of the things we inherit in our genes are completely random. This is known as genetic drift, a phenomenon that happens because some individuals leave behind more offspring than others do. Their genes are more likely to be spread throughout the population, but it’s not because natural selection decided that those genes necessarily offer any added benefits. In fact, it’s even possible that a few of those genes are detrimental. Genetic drift is part of evolution and something that defines the genetic fingerprint of a specific group, but it doesn’t work by promoting adaptations that will help our species in the future.
Genetic drift isn’t exclusive to humans, but a team of researchers from the Institute of Statistical Science in Taipei, Taiwan, created an algorithm to figure out how it affects the frequency of alleles in human populations. Alleles are alternative versions of a given gene that come about through mutations. The team accessed data from the 1,000 Genomes Project, a database of single nucleotide polymorphisms (SNPs), which are common genetic variations caused by a difference in a single nucleotide within a DNA sequence. The researchers then used their algorithm to analyze recurring patterns of alleles in populations from different continents, as well as in groups within those populations.
“At the global scale, genetic differences between subjects faithfully reflect the well-known history of human population migration and mixing,” they said in a study recently published in Scientific Reports. “In contrast, when examining the allele frequency patterns of individual loci, we discovered many minor yet non-negligible…evolutionary trajectories in the human genome.”
Out of 78 million SNPs, the researchers found 71 patterns that tell the ancient history of how allele frequencies ended up being arranged in particular ways among various groups. It was hardly surprising that over 90% of such variants occurred with more or less the same frequency no matter what continent the population was from. The locations of most allele frequency patterns are scattered throughout chromosomes and are usually found together in “hot spots.” These narrow segments of DNA are linked to gene functions and observable phenotypical (body) traits.
Then the team used what they called a local ancestry inference algorithm to look deep into chromosomes and determine what ancestral groups an individual is descended from. The results from this algorithm were then checked against data from 1,000 Genomes and Human Genome Population Diversity (HGPD) data. It turned out that most allele patterns observed were synonymous with simulations that highlight the randomness of genetic drift. But there were also minor differences that suggest drift isn’t the only evolutionary process influencing the genetic profile of an individual or population.
Many findings were consistent with the migration of human ancestors out of Africa and into Europe, East Asia, and South Asia. Allele frequencies in African populations were found to be distinct from those of Eurasians in 1.9 million locations on their DNA. The separation of African and East Asian populations from populations in Europe and South Asia was evidenced by variants in 570,000 locations. This reflects the known history of human migration, which has Eurasians as the first to break from their African ancestors and trek through Europe and East Asia. South Asian populations arose from admixture between groups from Central Asia and migrants who first traveled from West to East Asia before heading south.
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