"How to be human" - how to define human beings and understand their uniqueness as human beings is a complex and challenging problem. The rise and development of genetics have provided a new perspective for us to understand the origin and uniqueness of modern humans from a biological perspective - more than 20 years ago, the first sequencing of the human genome observed genetic differences and divergence times between modern humans and chimpanzees; The completion of the Human Genome Project has revealed the extensive genetic diversity of modern humans; The discovery of the genomes of early modern humans and extinct ancient humans provides new evidence and insights for exploring the pathways of human migration and evolution in the past. These groundbreaking works have brought us closer than ever to answering this question.

On the occasion of its 50th anniversary, Cell released a special issue discussing the cutting-edge scientific question of "what makes a person" from a genetic perspective. Due to her contributions to the field of human evolution research, Fu Qiaomei, a researcher of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, was invited to write a critical article on the evolution of modern people. This study interprets the development process of modern human genetic characteristics from the perspective of paleogenomics, explores the history of human migration and fusion patterns, population size, adaptive variation, and diversity in the past, and provides insights into the differences and dominant characteristics of modern humans from other extinct human populations and other species. On February 29th, the related results were published online in Cell under the title of Incident genes and the evolutionary path of modern humans.

By directly comparing the genome sequences of modern humans and extinct ancient humans, researchers can closely track the origin of modern humans and the changes in their important phenotypes, thereby distinguishing their genetic characteristics from Neanderthals, Denisovans, and others, and exploring the advantages and fundamental reasons why modern humans have survived compared to extinct ancient humans to this day. This direct method is theoretically a powerful tool. However, due to the limited genomic data available for extinct ancient and early modern humans, the genetic diversity of these ancient populations has not been fully understood, which limits the use of this method.

Although important clues have been discovered in existing datasets and studies, only 7% of the sequence range found to be unique to modern humans and not present in the incomplete lineage of extinct ancient human mixed race or ancestral populations. Within this sequence range, genetic variations related to neural function and RNA splicing have been discovered, while more other clues remain to be studied.

The article proposes that modern humans do not have a unique genome that clearly identifies themselves and distinguishes them from other groups or species, but a variety of genetic variants related to height, disease immunity, cold resistance, skin and eye color, dietary structure, etc. constitute important genetic characteristics - genetic diversity. Although this diversity is only a small part of the prehistoric human genetic diversity transmitted by the ancient genome, it has played an important role in human development history.

By decoding the ancient genome information of extinct ancient humans and early modern humans, researchers can clarify the genetic differences between these human populations, better understand their behavior and survival details, such as population size, family structure, reproduction methods, migration paths, and adaptation to climate change, pathogen transmission, lifestyle innovation, etc, This provides a new perspective on exploring the advantages and characteristics of modern people's sustained expansion and development at the group level.

Based on the analysis of existing relevant achievements, the article proposes that there are indeed some differences between early modern humans and extinct ancient human populations. For example, the effective population size of early modern human populations has always been larger than extinct ancient human populations such as Neanderthals, which helps modern humans maintain a high level of genetic diversity over a longer period of time and over a larger spatial range, as well as being more flexible in responding to constantly changing environmental conditions. For example, although early modern people and Neanderthals both practiced female exogamy, searching for female spouses outside their closely related small groups, the early modern population maintained higher genetic diversity, meaning that their direct ancestors had distant genetic relationships. The genomes of Neanderthals and Denisovans indicate signs of inbreeding in their direct ancestors. In addition, another prominent feature of modern people is their rapid and widespread group migration and expansion. Modern humans have ventured out of Africa, not only occupying all the previously extinct territories of ancient humans, but also spreading to more places such as the Sahara Desert, the Americas, and Oceania.

Although it is not possible to explain the continuous expansion of modern human populations and the extinction of ancient human populations through a single genetic phenomenon, the article proposes a positive correlation between population size and individual adaptability, that is, a more extensive and closely connected clustering network is more conducive to individual survival and reproduction. This is known as the "Ali effect". The Ali effect has had an impact on assisting modern people in collaborative activities such as resource development, defense, and mate selection.

In addition, the ancient genome has also played a role in revealing the adaptation mechanisms of modern humans to different environments. For example, mutations in the EDAR gene in northern East Asia may increase in frequency during the selection of low UV environments during the last ice age, while variants of the EPAS1 gene from the Danisova people may help high-altitude residents survive in high-altitude areas. Many adaptive genes related to local dietary structure, pathogen immunity, and lifestyle changes have also been discovered one by one. The above achievements have filled the relevant gaps in the evolution of modern humans and highlighted the crucial role of adaptation in human development history.

The increasing mobility and adaptability of modern humans means that there are still many ancient genomes that need further discovery and research. The two methods summarized by Fu Qiaomei's team for tracking the evolution of modern humans - direct and indirect methods, although limited by the limited amount of existing paleogenomic data, demonstrate the contribution and potential of paleogenomics in answering the question of "why humans are human". The article discusses the similarities and relative advantages of modern humans over extinct ancient humans from both direct and indirect perspectives, as well as individual and group levels, as well as other species in their evolutionary processes. This provides a clearer research approach for further refining the evolutionary path and deep hierarchical structure of modern humans. In the future, with the sequencing and research of the genomes of early modern humans and extinct ancient humans at more critical times and locations, more new evidence and thinking will be brought to answer "who we are and where we come from.".

The research work was supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences.

Paper link:

论文链接

The events that occurred in prehistoric history of modern people have increased the overall suitability of the population, promoting further survival and diffusion of modern populations worldwide.