Where did we come from? What did our ancestors eat? What adversities did our ancestors face? Why did some of our ancestors suddenly disappear?
These and many such questions have fascinated people for a long time. Ancient DNA (aDNA) studies powered by cutting-edge genomic techniques have opened a window into the past, providing unprecedented insights into the genetic makeup of our ancestors. And by extracting and analysing DNA from ancient skeletal remains, scientists can reconstruct the genetic profiles of these people.
Studies of such ancestral DNA have provided glimpses into the genetic diversity and population dynamics of ancient communities, their migration patterns, interactions, and adaptations to local environments, and even into the diseases these people confronted and how the afflictions shaped human evolution.
For example, genomic technologies have given researchers a way to understand pathogens that spread in the distant past, and trace their origins and evolutionary trajectories. By reconstructing the genomes of these lifeforms, they have been able to piece together the emergence, spread, and adaptation of infectious diseases throughout human history.
What can ancestral DNA say about health?
In a number of recent papers, researchers have also reported being able to use sequences of aDNA to understand genetic diseases that may have affected ancient humans, and through that open windows onto the medicines and tools that early human communities used. Such insights enrich our knowledge of evolutionary history as well as have implications for modern healthcare, since they can teach us about the diseases to which our genes have rendered us susceptible as well as how health disparities arose between different populations.
For example, some of the more common genetic diseases are the result of chromosomal abnormalities. Many chromosomal abnormalities result in chromosome number changes – that is, extra copies or deletions of entire chromosomes – resulting in different clinical syndromes. For example Down’s syndrome is caused by an extra chromosome 21; Klinefelter’s syndrome due to an extra X chromosome; and Turner syndrome by the loss of one of the two X chromosomes in women.
How is ancestral DNA linked to a disease’s history?
Chromosomal karyotyping is a method to visualise the complete set of chromosomes in a cell, and is among the best techniques to diagnose such abnormalities. However, karyotyping requires live cells, which in turn requires scientists to adopt laborious methods to culture and stain them.
But thanks to advances in the last decade, scientists today can fortunately use whole-genome sequencing data from fragmented and/or degraded DNA to understand chromosomal abnormalities. Scientists have since adopted these approaches to study chromosomal abnormalities in aDNA as well.
For example, on January 11, researchers at the Francis Crick Institute in London published evidence of some of the earliest known instances of Turner syndrome, Kinefelter’s syndrome, and Down’s syndrome in aDNA dating from the Iron age in Britain.
Similarly, a research group from Italy, Germany, and the U.S. reported an interesting analysis of genetic variants associated with cardiovascular diseases in modern humans. They studied DNA isolated from 22 mummified individuals from a variety of geographical regions and time periods. Some 17 samples from ancient Egypt were dated to 3600 BC whereas those from Bolivia, Peru, Switzerland, and Australia were from 1500-1900 AD.
These scientists used a novel approach to enrich specific parts of each genome that we know are associated with atherosclerotic cardiovascular disease in modern humans. Then, once they had sequenced these parts, the scientists computed the ancient people’s risk of developing the disease based on 87 genetic variants that mapped to 56 genes – also well-studied in modern humans. This way, the team concluded that five of the mummified samples had significantly high risk of developing cardiovascular disease and two had calcified heart vessels, suggesting they already had the disease.
In all, the scientists said they believe cardiovascular disease has been widespread in human populations for at least 5,000 years.
How can ancestral DNA be linked to diets?
Insights into the lifestyles of ancient humans can also be gleaned from their genetic remains. One such material is pitch from the birch tree. There is some evidence that ancient humans extensively used birch pitch to repair stone tools and possibly fix arrowheads. Microbes from the pitch sample can thus reveal information about the oral health of the individuals who chewed it.
In a January 18 study, for example, scientists from Finland, Norway, Sweden, and Turkey analysed DNA from three pieces of chewed pitch estimated to be around 9,500 years old, obtained from a site in Sweden. Upon sequencing the pitch samples, the scientists identified organisms associated with the sort of imbalance of microbial species observed in people with inflamed gums (periodontitis). The team also matched DNA with a number of plant and animal species, hinting at the ancient people’s diet.
What else can ancestral DNA reveal?
Studies of aDNA could also provide big clues about the creation and development of stone tools. In the 1930s, for instance, researchers dug a cave in Ranis, Germany, where they identified a number of ancient stone tools. This site was believed to have been occupied by an old human population, from around 50,000 years ago, when modern humans, neanderthals, and denisovans coexisted. So the question was who actually made these tools.
A tide of interest in this question prompted archaeologists to re-excavate the cave more recently, when they found several bone remains. When they sequenced genetic material from these bones using high-throughput sequencing, the DNA sequences they found unequivocally pointed in the direction of Homo sapiens. When they dated the samples using radiocarbon dating, the samples were found to be some 45,000 years old.
The authors are senior consultants at Vishwanath Cancer Care Foundation and Adjunct Professors at the Indian Institute of Technology Kanpur. All opinions expressed are personal.
