Human Origins: Climate adaptation linked to early human ancestor

The story of humanity’s emergence from Africa is ancient, yet relatively brief compared to the antiquity of Earth and all life found on it.

Our planet is approximately 4.5 billion years old. Life is believed to have emerged around 3.5 billion years ago. The dinosaurs went extinct approximately 66 million years ago. Homo sapiens—our species—came into being about 300,000 years ago.

But ours is just the only surviving species of a lineage of upright-walking hominins that evolved in Africa.

For millions of years before the arrival of Homo sapiens and Neanderthals, other Homo species walked the earth, and some even made it far beyond their native territory in Africa.

One of these was Homo erectus, an archaic human-like species.

Short but robust, this proto-human with which modern humans share a common ancestor made it all the way to Indonesia and survived for close to 2 million years.

Now, a team of scientists say they’ve uncovered evidence showing that Homo erectus spread its range well beyond Africa by learning to adapt to a changing climate. This trait was once thought to be exclusive to modern humans.

Publishing their findings in the journal Communications Earth & Environment, the team says their discovery suggests “archaic humans possessed an ecological flexibility previously attributed only to later hominins.”

Specifically, they say they’ve uncovered evidence that Homo erectus survived in “hyper-arid landscapes” by returning to the same water sources repeatedly, essentially setting up camps close to water to weather the extended dry period.

This adaptability likely primed the species for its exit out of Africa and across Eurasia, Mercader et al. argue in their newly published paper.“Homo erectus exhibited far greater adaptability to diverse ecologies than previously understood,” they wrote, “with a capacity to persistently occupy extreme environments.”

Bones and tools

Their research centers on Olduvai Gorge in Tanzania, made famous by the Leakey expeditions. Work was primarily conducted at Engaji Nanyori and the Ngorongoro Conservation Area.

There, the archaeologists say they uncovered the butchered remains of animals and the tools Homo erectus used to butcher them. The animal’s bones show distinct signs of cutting and scraping, evidence that the early archaic humans used stone tools to get as much meat off the bones as they could.

A bit of geology and paleontology played a role, as well. The study details how team members were able to uncover ancient fluvial dynamics and sedimentary stratigraphy showing how water sources emerged and dried up over time. Fossil plant evidence revealed the types of vegetation that were growing at these sites at the time.

They say the evidence reveals big changes in climatic conditions over time, coinciding with Homo erectus’ continuing presence throughout those changes.

Authors Julio Mercader of the University of Calgary and Paul Durkin of the University of Manitoba led the research. In a synopsis, they said 

Through combining “archaeological, geological, and paleoclimatic data” the researchers say they were able to cobble together a picture of what the region was like during the time Homo erectus inhabited it.

Stretching way back in time to when the species of the famed Lucy fossil lived, we know that one of the first key evolutionary changes that early apes experienced that gave rise to humans was bipedalism—walking upright. It’s theorized that this adaptation was not only more energy-efficient, but it also freed up early human ancestors’ hands for other work. This, combined with a more protein-rich diet, may have fueled brain development and intelligence.

A story written in evolution

Species of hairless upright-walking apes endowed with endurance and a capacity to organize and hunt collectively are uniquely evolved to survive in grasslands. Researchers led by this pair of Canadian university professors discovered something rather peculiar in northern Tanzania.

They argue that over approximately 200,000 years, this region of Olduvai was almost a desert, inhospitable to all but the hardiest of species, typically those that evolved to survive in desert or semi-desert conditions.

Like Homo sapiens, scientists believe Homo erectus evolved in wetter savanna habitats. So how did they survive and thrive in near-desert conditions? By learning to cope with changes in their environment, the team says.

“Behavioral adaptions included returning repeatedly over thousands of years to specific rivers and ponds for fresh water, and the development of specialized tools,” they said.

The tools in question include “scrapers and notched tools” they discovered during their archaeological digs. They believe Homo erectus refined these tools from earlier, more basic versions in a bid to improve the efficiency with which they could butcher bones and harvest all the meat and marrow.

The timing of these adaptations is important, too. The authors argue that Homo erectus appears to have learned to adapt and survive in a near-desert environment before migrating out of Africa, through the Middle East, and onward to destinations in East Asia and portions of modern Europe.

Their findings add to evidence that human origins and evolution were heavily driven by our earliest ancestors’ relationships with bodies of water.

Following the water

Scholars are organizing a conference in Belgrade for September this year specifically on this theme. The Intertwined Pasts conference is now calling for papers describing how water played a hand in the emergence and migrations of archaic, now-extinct hominins and prehistoric humans.

“A growing body of evidence has been recovered from several prehistoric sites showing that hunter-gatherer interaction with aquatic environments played a significant role in subsistence strategies, cultural development, and technological innovation,” conference organizers Mariana Nabais, Anna Rufa, Asier Garcia-Escarzaga, and Asia Alsgaard said in their call for papers.

“The use of waterscapes—including rivers, lakes, wetlands, coastal areas, and their resources—has been considered as a critical aspect of human adaptation,” they added.

Mercader et al. concur.

Their discovery gives us a bit of a clearer picture of how the earliest human ancestors and relatives may have evolved and then adapted to persist in an array of climates and habitats.

The earliest human-like species evolved the ability to walk upright, and then gradually attained higher orders of intelligence over subsequent generations spanning millennia. Out of this process, species like Homo erectus emerged.

Homo erectus is believed to be among the first hominins to disburse beyond Africa. They may have achieved this ability by first learning to adapt to harsh environmental changes in their home terrain—namely, a dry spell that lasted thousands of years and turned once lush savanna into near-desert landscapes.

Through strategic use of water resources and specialized toolmaking to improve hunting and animal butchering, Homo erectus may have acquired the ability to conquer other dry lands farther east. This and other pressures may have propelled them out of Africa, potentially paving the way for other Homo species to follow.

Eventually, one dominant relative did so—Homo sapiens, the last surviving hominin that has acquired the ability to adapt and survive in a wide range of extreme climates, from harsh deserts to Arctic conditions at higher latitudes.

Modern humans subsequently colonized every continent and even some of the remotest Pacific islands and archipelagos. At least, that’s one possible interpretation.

The researchers behind the Mercader et al. paper say their work sheds new light on the amazing adaptive capacity of the earliest human ancestors, traits that likely facilitated their survival for millions of years before all but our kind became extinct.

“These findings suggest archaic humans possessed an ecological flexibility previously attributed only to later hominins,” they said. “This adaptability likely facilitated the expansion of Homo erectus into the arid regions of Africa and Eurasia.”