To what extent may ancient and frequent climatic changes have shaped human evolution

Frequent climate changes may have orchestrated where to turn down Which species have lived over the past two million years and how humanity has evolved.

Fluctuations in temperature, precipitation and plant growth encouraged ancient human migrations in and out of Africa that enhanced the ability to survive in unfamiliar environments, climate physicist and oceanographer Axel Timmermann and colleagues said. Based on how the timing of ancient climate changes coincided with the comings and goings of different fossils to turn down Species, researchers have produced a new – and controversial – blueprint for human evolution. Timmerman, of Pusan ​​National University in Busan, South Korea, and his team present this scenario on April 13 temper nature.

Here’s how these scientists tell the story of humanity, nearly two million years ago. By then, standing man It has already begun to wander outside Africa, while the species were called from East Africa H. Ergaster It is stuck close to its original area. H. Ergaster It may have evolved into a disputed species from East Africa called H. heidelbergensis, which split into southern and northern branches between 850,000 and 600,000 years ago. These migrations coincided with warmer, survival-promoting climate changes that occur every 20,000 to 100,000 years due to differences in Earth’s orbit and inclination that alter the amount of sunlight reaching the planet.

Then after traveling north to Eurasia, H. heidelbergensis It may have led to the emergence of Denisovans about 430,000 years ago, researchers say. And in central Europe, the harsh habitats created by repeated ice ages spurred its development H. heidelbergensis in Neanderthals between 400,000 and 300,000 years ago. Finally, in Southern Africa between 310,000 and 200,000 years ago, increasingly harsh environmental conditions accompanied the transition from H. heidelbergensis to H. sanewho later moved from Africa.

But some researchers confirm this H. heidelbergensis, As defined by its defenders, it contains too many fossils to be classified as a species.

An alternative view of the newly proposed scenario suggests that during that time H. heidelbergensis Live, closely related to turn down Clans are periodically divided, reorganized, and reared with strangers, without necessarily serving as distinct biological species (SN: 12/13/21). In this view, intermarriage between H. sane Groups across Africa 500,000 years ago eventually began producing physical structures typical of people today. If so, that would undermine the viability of the finely branched evolutionary tree of to turn down Species leading to H. saneas suggested by the Timmermann group.

The new scenario is derived from computer simulations of the likely climate over the past two million years, at 1,000-year intervals, across Africa, Asia and Europe. The researchers then examined the relationship between the simulation’s predictions of what ancient habitats were like in those areas and the dates of human fossils and known archaeological sites. These sites range in age from about 2 million to 30,000 years old.

Previous fossil evidence suggests that H. erectus It spread to East Asia and Java (SN: 12/18/19). Timmermann’s climate simulations indicate this H. erectusBeside H. heidelbergensis And H. sane, adapts to increasingly diverse habitats during long journeys. These migrations stimulated brain development and cultural innovations that ‘may have made [all three species] Global hikers as they were,” Timmerman says.

New habitat simulations also indicate this H. sane It was especially good at adapting to hot and dry regions, such as northeastern Africa and the Arabian Peninsula.

Climate, habitat and fossil data were not sufficient to include additional proposals to turn down Species in the new evolutionary model, including H. fluorescence in Indonesia (SN: 3/30/16) And h. Naledi In South Africa (SN: 5/9/17).

It has proven difficult to show more specifically that ancient environmental changes caused transitions in human evolution. For example, the previous proposal that led to abrupt climatic shifts led to resource-rich, rainy expanses of the coast of South Africa, creating conditions where H. sane then evolved (SN: 3/31/21), still lacks an adequate climate, fossils, and other archaeological evidence.

Paleoanthropologist Rick Potts of the Smithsonian Institution in Washington has developed another influential theory of how climate fluctuations affect human evolution that is still open to debate. This resulted in a series of climate-induced booms and busts in resource availability, which began about 400,000 years ago in East Africa. H. sane It evolves as a species that has an extreme ability to survive in unpredictably changing environments, says Potts (SN: 10/21/20). But the new model refers to the old one H. sane They often migrate to new but relatively stable environments, Timmerman says, which undermines support for Potts’ hypothesis, known as variance selection.

The new findings must be compared with long-term environmental records at several well-studied fossil sites in Africa and East Asia before a judgment can be made about the selection of variation, says Potts.

Paleoclimatologist Rachel Lubbian of the Lamont-Doherty Earth Observatory in Palisades, New York says the new model “provides a fascinating framework” for assessing ideas such as variance selection over tens or hundreds of years that were closely related to the ancient. to turn down Migrations.

Currently, much is still veiled from the ancient landscape of human evolution.

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