Mysteries in Science: Why has only Homo sapiens survived?

Hiroki Oota

(Professor, Department of Biological Sciences)

There is only one species of human being on our planet today: Homo sapiens. But we are not the only human beings who have walked on the Earth. As is the case for other living things, the path of human evolution was not linear, but rather branched like a tree growing toward the sky. These separate branches gave rise to humans with different morphological characteristics, with names you may have heard: Australopithecus, Peking Man, and Neanderthal Man. While some died out, the descendants of others have lived on. We Homo sapiens are the ones who have survived from the distant past to the present, but why, out of all the many kinds of human beings once on the Earth, are we the only ones to have survived?

In the last 20 years or so, dramatic developments in genome analysis techniques have led to revolutionary advances in a wide range of fields, including medicine, drug discovery and biology. Genome analysis has also had a huge impact on the study of human evolution. Analysis of the diversity of an individual's genome can reveal their phylogeny and the evolution of the population to which that individual belongs. Such research has yielded dramatic results, especially in European countries and the United States.

Paleogenomics is one such field of research using applied genome analysis. By collecting the trace amounts of DNA that can be found in the remains of organisms that lived in the past, we can extract their genomic information. Genome analysis of extinct creatures, such as mammoths found in the permafrost of Siberia and ground sloths that once inhabited South America, reveals the secrets of survival of closely related species that are alive today. Analysis of the Neanderthal Man genome is yet another example of this research. Until 30,000 to 40,000 years ago, both Homo sapiens and Neanderthal Man inhabited Europe and Western Asia at the same time. Neanderthal skeletal morphology was very different from that of Homo sapiens, and their culture, found in archaeological sites, was also distinct. Are modern Europeans the descendants of Neanderthal Man, or are they totally unrelated? Perhaps it is more appropriate to use the label Homo neanderthalensis; in other words, a separate species? However, the Neanderthal genome sequence published in 2010 revealed that between one and four percent of the genome of modern humans living outside the African continent is of Neanderthal origin. This indicates that these two species of Homo, whose branches should have diverged by about 500,000 years ago, met and interbred again about 50,000 years before the present day.

In the 10 years since this paper appeared, research groups in Europe and the United States have published a flood of papers on the results of paleogenomic analysis. In Japan, however, such research has not progressed to the same extent, because Japan has a warm and humid climate and volcanic soils with high levels of acidity, which means that even if bones remain in the soil, any DNA left in the bones will be of extremely poor quality. Only since 2017 has information on the Jomon people genome finally begun to appear in the scientific literature. In 2018, our research group also published a paper in the journal Science describing the draft sequence of the entire genome of human bones found at a Jomon site in Aichi Prefecture.

The Japanese archipelago is located at the eastern end of the Eurasian continent. How did Homo sapiens arrive here in the Far East from the African continent? With the arrival of paleogenomic analysis, the door to exploring the path and secrets of our survival has just opened.

Figure : Replica of Jomon people bones in the outdoor exhibition at the Yoshigo Shell Mound Museum in Aichi Prefecture.

― This article is from the "Mysteries in Science" series in The Rigakubu News ―

Translated by the Office of Communication

― Office of Communication ―