Nobel Prize for Medicine & Physiology 2022: Svante Pääbo and the human evolution story

In 2008, Svante Paabo, the Swedish scientist and team made an accidental discovery of a finger bone in a cave in Siberia. Decoding the genetic information from it led him to throw new light on human evolution. Fourteen years later, his ground breaking work has won him the Nobel Prize for Medicine and Physiology in 2022.

The fragments of the bone dated to 40,000-years and found in a place called Denisova contained exceptionally well-preserved DNA (Deoxyribonucleac acid), which Pääbo’s team sequenced. It led to a discovery of a previously unknown Hominin, which was aptly named Denisova.  The DNA sequence was unique compared to those of the Neanderthals and Homo Sapiens.

Paabo also sequenced the genome of the Neanderthal man in 2010. The Neanderthal man is considered to be extinct relative of the Homo sapiens (present humans).

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The Swedish scientist went on to show that gene flow had occurred between Denisova and Homo sapiens. This relationship was first seen in populations in Melanesia (present Fiji, Vanuatu, Papua New Guinea and the Solomon Islands ) and other parts of South East Asia, where individuals carry up to 6% Denisova DNA, he explains.

Pääbo’s revelations on the genetic differences that distinguish the living humans from the extinct hominins provide the basis for a new understanding of our evolutionary history and what makes us uniquely human.

According to Paabo, when the Homo sapiens migrated out of Africa, at least two extinct hominin populations inhabited Eurasia (Europe and Asia). The Neanderthals lived in western Eurasia, while Denisovans populated the eastern parts of the continent.

During their expansion the Homo sapiens  not only met and interbred with Neanderthals, but also with Denisovans, the research established.

In short, there is a definitive flow of the DNA from the Denisovans and the Neanderthals to the Homo sapiens. The nearly 2 decades of research by Pääbo has given rise to an entirely new scientific discipline called Paleogenomics.

 In recognition of the far reaching consequences of Paabo’s contributions, the Nobel Committee decided to bestow the award on him solo. Most of the Science Awards in recent years have been shared because of the competitive and monumental work done by different scientists across the world.

The Indian contributions

In India the interest in the quest for human ancestry has been high with research done by the Hyderabad-based, CSIR-Centre for Cellular and Molecular Biology. The Laboratory has also set up an Ancient DNA laboratory. Over the past two decades led by Dr Lalji Singh and Dr K Thangaraj, substantive studies have been done to throw light on the mainland Indians their links to tribes of Andaman and Nicobar to the humans out of Africa using DNA fingerprinting and genome sequencing.

The Institute is also collaborating with global research bodies, including the Harvard and Cambridge Universities and some European to trace the antiquity and identity of various population groups.

Interest from a young age

Interest in human evolution was ignited in a young Paabo from his visits to Egypt and the Sphinx and the Pharaoh’s. He began studying the genes from samples of DNA from ancient samples in his quest to find answers to the puzzle of when, where and how human being came to the planet.

Palaeontology and archaeology are important fields of study in human evolution. According to present understanding, the Homo sapiens, first appeared in Africa approximately 300,000 years ago, while our closest known relatives, Neanderthals, developed outside Africa and populated Europe and Western Asia from around 400,000 years until 30,000 years ago, at which point they went extinct.

The sequencing of the entire human genome by 2000 gave a fillip to human evolution and population studies. It facilitated studies of the genetic relationship between different human populations. However, studies of the relationship between present-day humans and the extinct Neanderthals required the sequencing of genomic DNA recovered from archaic specimens.

This is where the chance finding and sequencing of a region of mitochondrial DNA from the 40,000-year-old piece of bone played a crucial part. Comparisons with contemporary humans and chimpanzees proved that Neanderthals were genetically distinct.

Early interest in ancient DNA

Paabo’s quest to study Neanderthal DNA began as a postdoctoral student with Allan Wilson, a pioneer in the field. He was excited at the possibility of using modern genetic techniques but encountered difficulties. A major reason is that with time DNA becomes chemically modified and degrades into short fragments. After thousands of years, only trace amounts are left, and they are mostly contaminated with DNA from bacteria etc.

At the University of Munich, he worked on archaic DNA analysing DNA from Neanderthal mitochondria – organelles in cells that contain their own DNA. The mitochondrial genome is small and contains only a fraction of the genetic information in the cell, but it is present in thousands of copies, increasing the chance of success.

With these advancements Paabo and his co-workers set out to studying the relationship between Neanderthals and modern-day humans from different parts of the world. Comparative analyses showed that DNA sequences from Neanderthals were more similar to contemporary humans originating from Europe or Asia than to those from Africa. In modern day humans with European or Asian descent, approximately 1-4% of the genome originates from the Neanderthals.

By extending the application of paleogenomics, Svante Paabo and his group has completed analyses of several additional genome sequences from extinct hominins. With no genomes of extinct hominins from Africa sequenced due to their accelerated degradation of the DNA the links with the Homo sapiens from here eludes an answer.

Implications on human health

An interesting fallout of all these paleogenomics work is a peep into how the gene sequences from our extinct relative could influence the physiology of present day humans.

Already, they have shown that a EPAS1, a Denisovan version is common among Tibetans and provides the advantage for survival at high altitude. Other examples being probed are the Neanderthal genes that affect our immune response to different types of infection. Dr Paabo and associates are analysing the patterns of how COVID-19 affected different populations in Europe and the immunity levels.

What makes us uniquely human?

Homo sapiens is characterized by its capacity to create complex cultures, advanced innovations and figurative art, as well as by the ability to spread to all parts of the planet.

Neanderthals also lived in groups and had big brains. They also utilized tools, but these developed very little during hundreds of thousands of years. The genetic differences between Homo sapiens and our closest extinct relatives were unknown until they were identified through Pääbo’s seminal work, said the Noble Committee in its citation.

Paabo’s work has opened up the entire field of paleogenomics. Further researches in the future can solve more of the jigsaw puzzle in journey of the humans over the ancient to the modern.

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