DECODING MYSTERIES OF HUMAN EVOLUTION

INTERTWINED LIVES OF NEANDERTHAL, DENISOVANS AND Homo sapiens

SUBHASH WALIMBE

Former faculty, Deccan College Postgraduate and Research Institute

Email ID: subhashwalimbe@gmail.com

The UIAF and the entire Indian anthropology fraternity joins in saluting Svante Pääbo, a geneticist who unmasked the lives of ancient humans. He is awarded the Nobel Prize (2022) in Physiology or Medicine.

This year’s Nobel Prize in Physiology or Medicine has been awarded for pioneering studies of human evolution to Svante Pääbo, a geneticist at the Max Planck Institute for Evolutionary Anthropology, Germany. He pioneered the sequencing of the Neanderthal genome and the discovery of a new group of hominins called the Denisovans and is rightly called “the godfather of the field”.

Svante Pääbo was born on 20th April 1955 in Stockholm, Sweden to Noble laureate father Sune Bergström who won the Nobel Prize in Medicine in 1982. Svante Pääbo went to a medical school at the University of Uppsala and started teaching and simultaneously doing part-time research at the Department of Cell Biology, Uppsala and Roche Institute for Molecular Biology in 1980. He was awarded his Ph.D. degree in 1986 and began postdoctoral research at the Institute of Molecular Biology II in the same year. He did most of his laboratory studies in Germany at the University of Munich. He is currently serving as the Director of Max Planck Institute for Evolutionary Anthropology in Leipzig. In 2007, he was listed among 100 most influential people in the World by the Time Magazine. Svante Pääbo is a prolific researcher and has authored, co-authored 350 papers, several book-chapters and a book titled Neanderthal man: In search of lost genomes (2014) translated in 14 languages till date.

The span of his research is too vast, spawned the competitive field of palaeogenomics. Briefly speaking, Prof. Pääbo made his disciples trace how genes flowed between ancient hominin populations, and how these groups migrated, and consequently influenced bio-cultural scenario all over the world. More importantly these studies shed light on the origins of some aspects of modern human physiology, including features of the immune system and mechanisms of adaptation to life at high altitudes.

The most outstanding contribution of Pääbo lies in his attempts to develop ways of analysing DNA that had been damaged by thousands of years of exposure to the elements and contaminated with sequences from microorganisms and modern humans. During the early years of 1990s, the ancient DNA field was plagued by such concerns and considered one of the most frustrating areas of research. Thanks to methods developed in Pääbo’s laboratory, as well as the advent of new sequencing technologies, contamination is no longer that serious an issue. These efforts eventually led to work sequencing the Neanderthal genome, a landmark study.

The recent genetic analysis in the line led to the finding that Neanderthals and Homo sapiens interbred, and that 1 to 4% of the genome of modern humans of European or Asian descent can be traced back to the Neanderthals.

Pääbo’s techniques were also used to identify the origins of a 40,000-year-old finger bone found in a southern Siberian cave in 2008. DNA isolated from the bone indicated that it was from neither Neanderthals nor Homo sapiens but came from an individual belonging to a new group of hominins. The group was named the Denisovans, after the cave in which the bone was found. Ancient humans living in Asia interbred with this group, too, and Denisovan DNA can be found in the genomes of billions of people alive today.

Pääbo’s sequencing of ancient-DNA from Neanderthals, Denisovans and other hominins also has important implications for modern medicine. Although the proportion of the human genome comprised of archaic DNA is small, this material seems to punch above its weight, making an important contribution to the risks of diseases ranging from schizophrenia to severe COVID-19.

Pääbo’s students describe him as intense and driven, but also collegial and generous. His department at the Max Planck Institute for Evolutionary Anthropology has produced a generation of paleogeneticists who are pushing the field ever further. David Reich, a population geneticist at Harvard Medical School in Boston, Massachusetts, who worked closely with Pääbo on the Neanderthal genome sequence, is pursuing the ancient DNA experiments for Indian anthropology. He very proudly commented on Pääbo’s Nobel win, “an extraordinary recognition of this field maturing and of what he did in putting together everything that needed to be done to accomplish this miracle, which is getting ancient DNA from human remains”. He further adds “the fact that a good fraction of the people running around in the world today have DNA from archaic humans like Neanderthals is of important consequence to who we are…. So, I think that knowing that and trying to understand the implications of that for health is something that will be with us for the rest of our time as a species.”

I personally have experienced his generosity. In mid 1990s my team was struggling (in CCMB) for ancient DNA on our Deccan Chalcolithic sample, and after spending almost a couple of years (and lots of money) what we got is sheer frustration. We had lost all hopes and one morning I wrote to Pääbo about it and, I remember, in a couple of days we had his offer to try our sample in his Max Planck lab. Not only he offered his equipment but paid for all consumables and made one of his colleagues Mark Stoneking (his partner in Neanderthal DNA experiments) to guide us. We tried, but there also we failed. Yes, in that dark phase he advised us to publish our results, saying “getting negative results is also a good contribution to the subject”, because that was the time when we were working to refine our lab protocol. This is how that AJPA (2000) article came, “Discouraging prospects for ancient DNA in India” came about. ….. Even after 25 years conditions have not changed much, no unambiguous success so far. Rakhi Garhi success is still controversial, Roopkund was an exception, bones were not still dry.

Genetic data is being generated for several Indian extant populations in recent years. Yet, for several studies there remain serious issues about the sampling procedures. Population comparisons would be more meaningful only if sample represents a ‘endogamous mendelian’ group. Moreover, the main concern is that the genetic data can only speak about the migration of people and not the culture of the dispersing populations. The conjectures about language migrations can be substantiated only by linguistic evidence, texts, and archaeological data. If language transmission takes place through contact and spread of farming (not a spread of the farmers), then it will leave little signature in the genetic record. Similarly, if a small group of migrants become the dominant elite through military conquest or by economic supremacy they can impose their language on the general population, again without a significant sign in the genetic record. In this view, the hypotheses on ‘Ancestral North Indians’ and ‘Ancestral South Indians’ being floated by the molecular groups will remain debatable unless supported by high quality ancient-DNA data of Indian protohistoric populations, and unfortunately the preservation levels are very poor.

And in this regard, the continued efforts of Pääbo and Reich group are important to answer specific questions about the peopling of the Indian sub-continent. Probably we need yet another technical leap. Let us keep our hopes afloat!!

JOURNEY HAS JUST COMMENCED