Why are we protecting a climatic regime that almost caused our extinction?

New study shows how humans almost went extinct during glaciation 900k years ago.

The current climate regime…

The current climate regime has been marked by a series of glaciations, or ice ages, interspersed with warmer interglacial periods. This era is characterized by the expansion and contraction of vast continental ice sheets in the Northern Hemisphere, which have profound impacts on global climate, sea levels, and ecosystems.

These changes are driven largely by variations in Earth's orbit and axial tilt, known as Milankovitch cycles. These cycles influence the amount and distribution of solar radiation reaching the Earth, thus affecting global temperatures.

Our current climatic regime is relatively more dynamic than that of the preceding epochs. While past time periods also had cooler periods, they did not experience the same extensive glaciations of the present day. The onset of our current climate regime was marked by a global cooling trend, which set the stage for the repeated advance and retreat of ice sheets.

The shifting climates and habitats of our current climate regime, along with potential pressures from early human populations, led to significant evolutionary adaptations and a wave of megafaunal extinctions.

In comparison to previous climatic regimes, the current regime is notably volatile in terms of its climate oscillations. While other epochs in Earth's history certainly experienced climatic changes, the frequency and intensity of the glaciation cycles during recent times were unique and had lasting impacts on the planet's geology, ecosystems, and evolution of species, including humans.

Our near extinction 900k years ago…

Human evolution and our journey as a species have been marked not only by periods of growth and expansion but also by challenges and events that constrained populations and reduced genetic diversity. These constraining events, often termed "bottlenecks," can significantly shape the genetic makeup of the surviving population.

One significant bottleneck event in human history is believed to have occurred as our ancestors migrated out of Africa. Genetic studies suggest that all non-African populations descended from a relatively small group of Homo sapiens who left the continent. This is evident from the reduced genetic diversity observed in non-African populations compared to African populations.

Another proposed bottleneck occurred about 74,000 years ago after the eruption of the Toba supervolcano in present-day Indonesia. This eruption is thought to have led to a global volcanic winter, which could have dramatically reduced human populations. Some genetic analyses suggest that the number of reproducing humans during this period might have shrunk to a mere few thousand. However, the extent and impact of this bottleneck remain a topic of debate among scientists.

Throughout human evolution, the Earth has undergone several ice ages, periods of prolonged cold that expanded polar ice caps and glaciated vast regions. These conditions would have constrained available habitats and resources, possibly leading to localized bottlenecks for human populations.

In fact, a recent study published today in the journal Science titled, “Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition” found: