The Younger Dryas cataclysm brought death and destruction 12,900 years ago and triggered a global cooling event that lasted 1300 years.
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This video discusses the cultural changes during the early Holocene Epoch following the mass extinction and destruction of the Younger Dryas cataclysm. The Holocene is the current geological epoch that began after the Pleistocene epoch approximately 11,650 calendar years before present. The transition between these two epochs was caused by one or more extraterrestrial impacts that killed the megafauna in North and South America and triggered a global cooling event that lasted 1300 years.
The Younger Dryas global cooling event and the extinction of the megafauna 12,900 years ago are well accepted in the scientific community. Large animals had inhabited North America for thousands of years, and suddenly, around 45 genera disappeared along with the Clovis people who populated America at that time. The rich diversity of megafauna that included mammoths, mastodons, ground sloths, horses, camels, lions, giant armadillos, and saber-toothed tigers disappeared in a geological instant.
Research in Chile has also confirmed the extinction of megafauna in South America at the onset of the Younger Dryas. This image shows the stratigraphic distribution of megafaunal bones and dung fungi spores. The leftmost part of the figure marks with dots the occurrence of extinct megafaunal bones below, but not above the Younger Dryas Boundary. The right part of the figure corroborates the extinction by mapping the concentrations of spores of Sporormiella dung fungi. These spores act as a rough indicator of the number of herbivores in a given area. The spores do not appear in the strata above the Younger Dryas Boundary for a long time until modern animals appear.
Some scientists have argued that the megafauna became extinct due to human hunting or sudden climatic changes, but it is more likely that an extraterrestrial impact on the Laurentide Ice Sheet caused the extinction event and triggered a global winter. There is substantial evidence for the Younger Dryas Impact Hypothesis. Impact microspherules are found in great abundance at the geological Younger Dryas Boundary layer that was deposited 12,900 years ago. This layer also is associated with a high concentration of platinum, which is a metal that is more common in meteorites than in the surface of the Earth. The Carolina Bays are also evidence of the secondary impacts of glacier ice chunks ejected by the extraterrestrial impact on the Laurentide Ice Sheet. Well preserved Carolina Bays have a perfect elliptical geometry, which indicates that the bays originated as inclined conical cavities. Experiments provide support for the impact origin of the Carolina Bays.
The Carolina Bays were produced by the saturation bombardment of secondary impacts of glacier ice boulders. The major axes of the bays converge at the location of the extraterrestrial impact by the Great Lakes. The impacts of the ice boulders had energies equivalent to 13 kilotons to 3 megatons of TNT. There was no place to hide and the ice bombardment basically pulverized all the megafauna and the Clovis people all the way from the Rocky Mountains to the East Coast of the United States.
There is a substantial body of archeological work showing that the human population declined during the early Younger Dryas. The article by David Anderson, Albert Goodyear, James Kennett and Allen West presents three approaches that confirm this. One of the lines of evidence is the number of Clovis points found at 13,000 calendar years before the present, which is just before the onset of the Younger Dryas. One thousand years later there is a decrease in points that implies a decrease in the population of the study area in the dark outline.
The Clovis people disappeared at the onset of the Younger Dryas and they were followed by the Folsom people. The reduction in the number of points is evident when the distribution is compared to Clovis points in the same region. This graph demonstrates that the number of points of each style shows a decline followed by an increase consistent with the change in population. The archeological record clearly shows a decrease of population in the United States following the onset of the Younger Dryas.
The stress of surviving the Younger Dryas is recorded as a bottleneck in the human Y-chromosome at the end of the Pleistocene. The Y chromosome is responsible for the development of male reproductive organs, and it is passed only from father to son. The paper by Karmin with 100 authors proposes that the bottleneck was caused by a global change in culture. However, the Y-chromosome diversity started to decrease in all regions of the world exactly at the Younger Dryas boundary about 12,900 years ago, and it is not likely that similar cultural changes would have occurred simultaneously in regions widely separated by oceans, deserts, mountains and jungles. The mitochondrial DNA which is passed from a mother to her offspring indicates that the worldwide human population continued to increase in spite of the reduction of male population size. A graph in the paper by Karmin shows that 10 thousand years ago, there were 8 females for every male. Seven thousand years ago, during the most severe portion of the Y chromosome bottleneck, there were 17 females for every male according to the human genetic record.
A paper by Zeng, et al. tries to explain the Y-chromosome bottleneck as the result of competition between patrilineal kin groups. To explain the Y-chromosome bottleneck, Zeng, et al. considered and rejected Ecological or climatic factors, Neolithic founder effects from small populations, and an increase in intragroup social and material inequalities. Zeng, et al. proposed that the formation of patrilineal kin groups and intergroup competition among these groups, which disproportionately affected males, could have led to a reduction in Y-chromosomal diversity that was much greater than the reduction in male population size, while keeping the female population size relatively stable. The founder effect refers to the reduced genetic diversity that results when a population is descended from a small number of colonizing ancestors. When a new colony is started by a few members of a larger original population, the colony generally has reduced genetic variation compared to the original population.
Zeng, et al. rejected the idea that the Y-chromosome bottleneck was caused by ecological or climatic factors because they thought that such effects are small and cannot account for the one-to-seventeen disparity between male and female population sizes inferred from the data. However, a paper by Catalano, Bruckner and Smith found that cold ambient temperatures during gestation predict lower secondary sex ratios. They conclude that ambient temperature affects the characteristics of human populations by influencing who survives gestation.
The paper by Catalano says that cold ambient temperature influences the characteristics of populations by affecting selection in utero. Low temperatures may cull males in utero and leave a more robust cohort compared with males born in years with warmer mean temperature. This means that a prolonged period of cold weather, like the Younger Dryas, could have substantially reduced the ratio of human males to females.
Evolution can change the characteristics of a population very fast through natural selection. Humans evolved the ability to digest lactose in adulthood only about 9,000 years ago in areas where the milk from cattle, goats, and sheep was used as a large source of food. More than 70% of western Europeans can drink milk as adults, compared with less than 30% of people from eastern Asia. People who do not produce the lactase enzyme are lactose intolerant and experience bloating and other gastrointestinal symptoms if they drink milk. Avoiding starvation by adapting to a new food source was a very favorable genetic mutation for Neolithic humans at a time when the Younger Dryas cold event made it difficult to harvest anything.
Genetic drift is an evolutionary process caused by random events that change the frequency of a gene variant in a population to create a genetic bottleneck. The genetic drift game illustrates how the distribution of food affects evolution. A link to this game is provided in the description below. At the beginning of the game, there are five planaria worms of different colors. During each generation, five pieces of food are distributed at random among the five worms. The worms reproduce based on the number of pieces of food that they get. The worms that don't get any food die.
This is a sample run of the genetic drift game. We start each iteration by feeding the worms. The red worm does not get any food during the first generation and it dies. In the second generation the brown worm gets more food and increases its presence in the ecosystem. In the third generation, all the worms get fed and live to see another day. During the fourth generation, the yellow worm does not get any food and becomes extinct. The green worm starves during the fifth generation. In the sixth generation the brown worms outnumber the blue worms by a 3-to-2 ratio, but the blue worms get most of the food. By the seventh generation the blue worms are the only survivors.
There is a passage in the Old Testament where God creates humans and commands them to be fruitful and multiply, and replenish the Earth. Even though the Bible was written long after the Younger Dryas cataclysm, the choice of words in this translation is suggestive of harder times in the past. "Replenish the Earth" literally means to fill it again in order to restore the population to a previous level. After the extinctions resulting from the Younger Dryas, the survival of humanity depended greatly on the ability to reproduce. This requirement would have been remembered for thousands of years and then recorded in ancient manuscripts.
A paper published in 2020 by Randall Haas and several co-authors reported the discovery of remains of two prehistoric hunters at an Early Holocene site in highland Peru, including the 9,000-year-old remains of a young woman buried with a well-stocked big game hunting toolkit. Her burial included a comprehensive array of hunting and animal processing tools that together provided unusually robust support for her hunter status, including stone projectile points for felling large animals, a knife and flakes of rock for removing internal organs, and tools for scraping and tanning hides. Based on analysis of 27 individuals at sites associated with big-game hunting tools, the authors concluded that between 30% and 50% of Late Pleistocene and Early Holocene big game hunters in the Americas may have been women.
The idea that women actively participated in hunting 9,000 years ago is consistent with the high ratio of women to men during the Y-chromosome bottleneck. The paper by Hass included this illustration of a female hunter by Matthew Verdolivo.
Women outnumbered men by a ratio of 17-to-1 during the most severe portion of the bottleneck, but the mitochondrial DNA graph shows that the human population continued growing. This means that each man had to mate with seventeen women on the average, and each woman would have had more than one child that survived to reproductive age. The sex ratio imbalance probably gave rise to Neolithic matriarchal societies and cultural practices where women hunted along with the men. This period of human evolution would have favored men with a high sex drive that could mate with multiple women to keep the human population growing.
The increased male sex drive which was a favorable trait during the Y chromosome bottleneck may be considered reproachable today when monogamy is advocated by religious and civil laws. But biological instincts frequently circumvent cultural regulations. An article by the Institute for Family Studies reported that men are more likely than women to have extramarital affairs. A recent General Social Survey reported that 20% of men and 13% of women have had sex with someone other than their spouse while married. Perhaps infidelity has its roots in the genetic traits that evolved during the Younger Dryas Y-chromosome bottleneck, which was not so long ago in historical terms.
