Where do we, Homo sapiens, come from?

The next question is where the ancient Japanese 3000 years ago had come from originally? Now it is believed that the ancient Japanese people moved from the main land China through Korean peninsula around 3000 years ago with the skill of rice production. Now it is also believed that before this movement another one had been taken from the Eurasian continent by crossing frozen Japan sea on ice around 10,000-30,000 years ago. Those people moved all over Japan but now their descendants are only found in Hokkaido and Okinawa area which was scientifically concluded based on DNA sequence analysis of the people. Most people between the two different origin groups are believed to be mixed, leading to the current Japanese (ref. S. Saito, Origin of Japanese people (in Japanese), Kawade shinsho series (2022)) (Fig. 1).

 Then, another question is raised. Where the people in the Eurasian continent came from?  Now we have a firm evidence in terms of the origin of Homo sapiens itself. According to the scientific research, the first Homo sapiens appeared from a primitive man in somewhere of central Africa around 400,000 years ago or before. Then they had to move from Africa because of climate and food problems. Eventually they went to all over the world through the near east Asian area around 70,000 years ago. Then, they reached Japan around 30,000 years ago as described above.

During the transfer process of Homo sapiens they might have met Neanderthals who had moved from Africa to Europe, and near and central Asia around 400,000 years ago and then became extinct. Since according to a research result (ref. S. Saito, Origin of Japanese people) the time of existence of Neandelthalensis and Homo sapiens partly overlapped, a question is raised whether or not Homo sapiens and Neanderthalensis intercrossed. Dr. Svante Paabo (Swedish origin), director of Max Plank Institute for Evolutionary Anthropology at Leipzig, Germany, gave an answer for this question and obtained Novel Prize in Physiology or Medicine 2022. He and his colleagues published a paper in 2010 about this issue (A Draft sequence of the Neanderthal Genome, R. Green, S. Paabo et al. Science (2010) 328, p710-722). Dr. Paabo also published a monograph in terms of his research history of human evolution (Neanderthal Man: In Search of Lost Genomes, Basic Books (2014) ). Here a part of the research result is shown.

Since Charles Darwin proposed an evolution theory in 1859, evolution process among various biological species including human being has been established based on mainly morphological differences like shape of skull (Fig. 2, 3). Definition of species is capability of fertility among various organisms. Because of this definition, ancient organisms are difficult to tell whether or not two independent organisms are different species even if they look similar morphologically. However, now we can tell evolution process and relationship of various species depending on nucleotide sequence of DNA called genome sequence.

   Dr. Paabo and his colleagues successfully determined the whole genome sequence of Neandelthalensis and compared with that of Homo sapiens which was determined in 2002 originally by Dr. C. Venter and his colleagues. Dr. Paabo described in detail how they could determine the genome sequence of Neanderthalensis in his book and the paper of 2010 in Science. Their first challenge was recovery of DNA from a 30,000 year old bone. Another difficulty was contamination of DNA of bacteria or others in the bone. Eventually they were successful in distinguishing the genome DNA from contaminated bacterial DNA (almost 90 % of DNA in the material was from bacteria). He also emphasized how important the progress of DNA sequencing technique and machines were.　

　The result of comparison of genome sequences of Homo sapiens and Neanderthalensis shows that about 3% of the whole genomes are more conserved, compared to the other areas of the genomes. Based on this finding, they concluded that Homo sapiens and Neanderthalensis are intercrossed. The more conserved genes are related to genes involved in formation of skull shape and cognitive ability. In their paper published in 2004, based of partial genome sequences they mentioned that the gene for keratin contained in hair and nail are conserved well, while 97 % of the total genomes are less conserved. This suggests that the genes in this non-conservative genes might affect the human ability. One example is the genes required for sperm formation. Fertility of Neanderthalensis might be recessive compared to that of Homo sapiens, because of the sperm ability. People inheriting the Neanderthalensis genes for sperm formation might have disappeared eventually.

    Dr. Paabo discussed about experimental plans in the future like observation of effects by the conserved genes artificially introduced into culture cell lines, which may impact the cell function. Then, we may be able to realize what evolutional changes favorable for Homo sapiens are.