‘Bottleneck’ killed off 98.7% of humanity 900,000 years ago – study
A study published last week in the journal Science reported that the population of human ancestors crashed between 800,000 and 900,000 years ago, dropping to about 1,280 breeding individuals during the early and middle Pleistocene era, which is associated with a severe cooling phase about 900,000 years ago. This represented a drop of about 98.7 percent of the ancestral population and lasted roughly 117,000 years.
The climate was generally cold, and this era is best known for its massive ice sheets and glaciers that shifted around the planet and shaped many of the landforms we see on Earth today. This was the time that modern humans spread outside of the African continents, and other human species, like Neanderthals, began to go extinct. The Australian continent and the Americas also saw humans for the first time.
The team, composed of researchers from China, Italy, and the United States, used a fast infinitesimal time coalescent process (FitCoal) to determine ancient demographic inferences with modern-day human genomic sequences from 3,154 people. Fit Cioal projects current human genetic variation backward in time to estimate the size of populations at specific points in the past
“The fact that FitCoal can detect the ancient severe bottleneck with even a few sequences represents a breakthrough,” study co-author and the University of Texas Health Science Center at Houston theoretical population geneticist Yun-Xin FU said in a statement.
FitCoal helped the team calculate what this ancient loss of life and genetic diversity looked like utilizing present-day genome sequences from 10 African and 40 non-African populations. The ancient “bottleneck was directly found in all of the African populations, but only a weak signal of the existence of such was detected in all the non-African populations,” the authors write.
“The gap in the African and Eurasian fossil records can be explained by this bottleneck in the Early Stone Age chronologically,” study co-author and Sapienza University anthropologist Giorgio Manzi said in a statement. “It coincides with this proposed time period of significant loss of fossil evidence.”
An estimated 65.85% of current genetic diversity may have been lost due to this bottleneck in the early to middle Pleistocene era, and the prolonged period of minimal numbers of breeding individuals threatened humanity as we know it today. However, this bottleneck seems to have contributed to a speciation event where two ancestral chromosomes may have converged to form what is currently known as chromosome 2 in modern humans. With this information, the last common ancestor has potentially been uncovered for the Denisovans, Neanderthals, and modern humans (Homo sapiens).
The control of fire and the climate shifting to be more hospitable for human life could have contributed to a later rapid population increase around 813,000 years ago.
Dr. Gerald Schroeder, a scientist with over thirty years of experience in research and teaching, noted that this “bottleneck” in human history was also reflected in the Book of Genesis.
“The flood in the generation of Noah was a bottleneck,” Dr. Schroeder said. “In terms of genetics and human history, it limited our genetic diversity. Humans are very similar to each other. Other species have much more diversity. In terms of the Biblical narrative, we became a more condensed family of many, but lifespans dropped from 900 years to 90. Perhaps the flood selectively killed off only the people with a genetic predisposition to long life. Longevity is good for the individual but worse for the species. Shorter lifespans engender intellectual and spiritual diversity.”
“It should be emphasized that we are not talking about humans,” Dr. Schroeder emphasized. “The Biblical calendar of 6,000 years does not relate to the beginning of species. All animals have a nefesh (animal soul), but only Man has a neshama (human soul). Homo sapiens as a species did appear about 100,000 years ago, but they wouldn’t be recognized as a person in the same way that we are. They had a nefesh but didn’t have a neshama. In scientific terms, people, as Homo sapiens, go back 100,000 years. But the Bible’s definition of a person is different. It includes a neshama. Science will not see the break, the change that occurred in man 6,000 years ago when we received a soul.”
“The neshama is what gives us the ability to be compassionate for someone outside your immediate clan,” Dr. Schroeder said. “Animals have a nefesh and can be compassionate to their own clan, but they see anyone outside their clan as a threat. The ability to see the ‘other’ as something other than a threat, to have compassion and empathy, is what defines the neshama.”
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