70,000 Years Ago: A Pivotal Transformation in Human Evolution

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Our human origins trace back to Africa. While this has not always been clear, it is now widely accepted.

This truth can be understood in two ways. The earliest known species closely related to us emerged from Africa, dating back 7 million years. Additionally, the oldest representatives of our own species, Homo sapiens, also originated from Africa.

Here, I will focus on the narrative of modern humans originating in Africa and their subsequent migrations across the globe. The introduction of DNA sequencing technology in the latter half of the 20th century enabled comparisons between different populations. This research demonstrated that African populations exhibit the greatest genetic diversity, while non-Africans show relative genetic similarity (despite visible differences such as skin color).

This genetic distinction serves as a telling indicator. It suggests that Africa was our birthplace with a diverse population, from which all non-Africans descended from a smaller subset that left this ancestral home to settle elsewhere. Geneticists affirmed this idea as early as 1995, and further evidence has since supported this claim.

However, there is a discrepancy between archaeological evidence and genetic findings.

Genetics indicates that all living non-Africans are descendants of a small group that left Africa around 50,000 years ago. Aside from minor uncertainties about the exact timeline, this conclusion has remained consistent for two decades. Conversely, archaeologists highlight numerous instances of modern humans existing outside Africa long before this timeline.

In Greece, a modern human skull found in the Apidima Caves dates back 210,000 years. The jawbone from Misliya Cave in Israel has been dated to at least 177,000 years. Additionally, there are several debated sites in China that may contain remains of modern humans. “Moreover, there’s an ongoing discussion on the earliest inhabitants of Australia,” says Eleanor Scerri from the Max Planck Institute for Geoanthropology in Germany, with some proposing human presence as early as 65,000 years ago.

What is the explanation for this disparity? Has our extensive genetic data misled us? Or is it true that we all share a common ancestry tied to a significant migration event, while older remains represent populations that did not survive?

Scerri and her team sought to understand this conundrum.

African Environment

The researchers debated the habitats of modern humans in Africa. “Did they simply migrate across diverse African grasslands, or were they adapting to vastly different environments?” asks Scerri.

To address this question, they needed extensive data.

“We began by analyzing all archaeological sites in Africa dating back 120,000 to 14,000 years ago,” explains Emily Yuko Hallett from Loyola University in Chicago. The team constructed a database identifying the climate at various locations and times.

A significant shift was observed around 70,000 years ago. “Simply examining the data without complicated modeling shows this climatic change,” notes Andrea Manica from the University of Cambridge. The range of temperatures and rainfall suitable for human habitation had notably expanded, leading people to venture into deeper forests and arid deserts.

However, mere observation is insufficient; the archaeological record is inherently incomplete and often biased.

“In certain regions, no archaeological sites exist,” remarks Michela Leonardi from the Natural History Museum in London. This absence might not reflect a lack of human occupancy, but rather the lack of preservation. “In more recent periods, preservation is easier due to the increased data availability,” she adds.

Leonardi devised a statistical modeling technique to determine if an animal shifted its environmental range. Could humans have transitioned from grasslands to diverse habitats, such as tropical rainforests? The team initially thought this modeling would take two weeks, but it took five and a half years.

Ultimately, the statistics affirmed their initial observation: around 70,000 years ago, modern humans began occupying a broader range of environments. The findings were published on June 18th here.

Jack of All Trades

“At 70,000 years ago, our species appears to have transformed into the ultimate generalist,” states Manica. From this period onwards, modern humans adapted to a variety of complex habitats.

This could be misinterpreted. The team did not imply that prior to H. sapiens people were incapable of adaptation. In fact, studies of extinct human species highlight that adaptability has increased over time.

“Humans were inhabiting environments vastly different from the early stages,” observes Scerri. “We’ve found evidence of habitation in mangrove forests, rainforests, desert edges, and highlands like those in Ethiopia.”

It appears that this adaptability is what allowed Homo sapiens to thrive during environmental changes in Africa, while other species like Paranthropus did not; they remained too rigid in their lifestyle to adapt.

What likely transpired in our species 70,000 years ago is that existing adaptability became pronounced.

Some of this understanding only becomes clear when considering the diverse habitats humans occupied. “One might think of deserts and rainforests in rigid terms, but there are actually numerous variations,” explains Scerri. “There are lowland rainforests, montane forests, marshes, and periodically flooded woodlands.” The same diversity applies even within desert environments.

Before, H. sapiens “did not exploit the full range of potential habitats,” states Scerri. “But around 70,000 years ago, we see the beginning of this expansion into more types of forests and rainforests.”

This narrative intrigued me, as I had been contemplating an opposite idea.

Great Quarantine

Last week, I authored a piece about the extinction of local human groups: it appears that some H. sapiens populations vanished without a trace in modern genetics. After departing from Africa, they faced challenges in harsh environments, eventually succumbing during encounters with the first modern humans in Europe. These lost groups fascinated me. Why did they fail while others that entered Europe thousands of years later found much success?

The discovery that African groups expanded their environmental niches 70,000 years ago provides a partial explanation. If these later migrations involved more adaptable populations, they may have been better equipped to face the unfamiliar environments of Northern Europe—and subsequently Southeast Asia, Australia, and the Americas where their descendants would eventually journey.

A crucial point: this does not suggest that all populations 70,000 years ago thrived. “Not all humans instantly turned into successful populations,” Scerri explains. “Many of these groups disappeared, both inside and outside of Africa.”

Moreover, as with any significant discovery, this study introduces as many questions as it resolves. Specifically: what triggered modern humans to become more adaptable around 70,000 years ago?

Manica notes that skeletal morphology supports this idea. Ancient fossils classified as H. sapiens today exhibit only some of the traits we typically associate with modern humans. “Starting around 70,000 years ago, we broadly witnessed the emergence of many of these characteristics as a collective,” he asserts.

Manica posits that moving into new environments may have facilitated increased interaction between previously isolated populations. For instance, if two groups were separated by desert, they wouldn’t encounter or exchange ideas or genetic material until they learned to adapt to desert conditions.

“There may also be positive feedback,” suggests Manica. “With increased connectivity comes greater flexibility… breaking down barriers and fostering further interaction.”

To conclude, in a story about these lost populations, I mentioned that one of the greatest challenges for human groups was isolation. Without neighbors, a small group can face extinction due to minor setbacks. If Manica is correct, the opposite trend unfolded in Africa. Populations expanded and became increasingly connected, leading to a surge of creativity that allowed our species to spread across the globe.

In this light, the success of the last migration out of Africa could be attributed to the need for community. Without others, we may be vulnerable and at risk of failing. The notion of preparing for an apocalypse alone in isolation may be fundamentally flawed.