Examining the Role of Climate in Early Human Migration from Africa

by Santiago Fernandez
Early Human Migration

The skull of Homo erectus, a species that ventured out of Africa around 2.1 million years ago, reveals insights into early human migration. Recent studies indicate that during this exodus, the northeastern region of Africa was lush and more vegetated than it is today, presenting a stark contrast to the current arid climate. This change in climate, creating a verdant corridor, likely played a crucial role in the migration path of these early hominins. Credit for this discovery goes to Mizmareck via Flickr.

A verdant passageway through the Sahara was formed around the time when our earliest ancestors began their journey out of Africa, as evidenced by recent research from Aarhus University.

Roughly 6 million years ago, a significant evolutionary divergence occurred in the forests of eastern Africa. Chimpanzees, our closest living relatives, evolved along one path, while our ancestors embarked on a different trajectory.

This divergence marked the start of a journey that would eventually lead to our ancestors descending from trees, adopting bipedal locomotion, and beginning to use tools, setting the stage for human global dominance.

Homo erectus, the first of our lineage to leave Africa around 2.1 million years ago, traversed through northeastern Africa and the Middle East, regions now largely desert, towards Europe and Asia.

A crucial sediment core in the Mediterranean Sea, receiving deposits from northeastern Africa, provides insights into the African Humid Periods that altered the landscape and vegetation. This is referenced in a study published in Nature Communications Earth and Environment.

The question of how Homo erectus managed to cross vast, inhospitable deserts has long puzzled researchers. Aarhus University’s new research, led by Rachel Lupien, suggests an alternative route taken by Homo erectus during their exodus from Africa.

Lupien explains that the Sahara undergoes periodic climatic shifts, known as the “Green Sahara” or “African Humid Periods,” where the desert transforms into a savanna-like landscape, similar to eastern Africa’s savannas.

“Our findings indicate that during the period of Homo erectus’ migration, the Sahara was more verdant than at any other point in the 4.5 million years we’ve studied. Consequently, they likely traversed through a lush corridor out of Africa,” Lupien asserts.

Homo erectus: Pioneers of Human Evolution

Over two million years ago, Homo erectus emerged in eastern Africa. This species was adept at crafting stone axes and likely harnessed fire. Physically, they were slightly shorter yet more robust than modern humans, with broader hips and a more elongated skull, but their brain size was approximately half of ours.

Homo erectus thrived for over 1.5 million years, spreading across Africa, Europe, Asia, and reaching Indonesian islands via the Malacca Strait, making them the longest-lived human species. Homo sapiens, our species, appeared around 300,000 years ago.

Source: Natural History Museum

Unearthing Climate History from the Seafloor

The Sahara is currently in a dry phase, with these cycles fluctuating approximately every 20,000 years. These “African Humid Periods,” as described by Lupien, vary in intensity due to two additional cycles lasting 100,000 and 400,000 years, respectively.

To understand ancient African climates, researchers turn to the seafloor. Core samples from the Mediterranean reveal climate patterns dating back millions of years. Sediments on the seafloor contain layers that are rich in information about past climates.

Leaf wax, a protective coating on plant leaves, serves as a vital biomarker in these sediment layers. While most plant components decompose quickly, wax molecules endure, providing a historical record of climatic conditions. For instance, the ratio of regular to heavy hydrogen in the wax indicates precipitation levels.

Moreover, carbon atoms in leaf wax differentiate between C3 and C4 plants, allowing researchers to discern the dominant vegetation type during various periods. During Homo erectus’ migration, there was a higher prevalence of C3 plants, suggesting a shift from desert to grassland and savannah environments.

Plant Photosynthesis: Diverse Strategies

Plants employ three primary photosynthesis methods: C3, C4, and CAM. While 90% of plants are C3, adapted to most environments except extreme aridity or heat, C4 plants thrive in hot, dry climates. CAM plants, constituting about 6% of plant species, are suited for even drier conditions.

Examples of C3 plants include wheat, oats, rice, and sunflowers. Maize, sugar cane, and amaranth are C4 plants, while succulents, cacti, and pineapples represent CAM plants.

Source: Khan Academy, Biology Dictionary, and Lex.dk

Climate Cycles and Africa’s Green Epochs

Milanković cycles, minor variations in Earth’s orbit, trigger the green periods in

Frequently Asked Questions (FAQs) about Early Human Migration

What role did climate play in early human migration from Africa?

Climate significantly influenced early human migration from Africa. Homo erectus, the first hominin to leave Africa, migrated around 2.1 million years ago through a lush and vegetated northeastern Africa, contrasting with today’s arid conditions. This greener environment, known as the “Green Sahara” or “African Humid Periods,” provided a more hospitable route for migration.

How did Homo erectus differ from modern humans?

Homo erectus, appearing over two million years ago, was slightly shorter and more muscular than modern humans, with wider hips and an elongated skull. Their brain size was about half that of modern humans. They were the first to use stone axes and possibly the first to control fire.

What are the “African Humid Periods”?

The “African Humid Periods” refer to recurring climatic shifts in the Sahara, transforming it from a desert to a savanna-like landscape. These periods occurred approximately every 20,000 years, with their intensity varying due to additional longer cycles of 100,000 and 400,000 years.

How is past climate information obtained from the seafloor?

Climate information from millions of years ago is obtained through core samples from the Mediterranean seafloor. These samples contain sediment layers with biomarkers, such as leaf wax, that provide clues about past climates. The chemical composition of these biomarkers, including hydrogen and carbon isotopes, reveals details about precipitation levels and the types of vegetation that thrived.

What are the different types of plant photosynthesis methods?

There are three primary photosynthesis methods used by plants: C3, C4, and CAM. C3 plants, making up 90% of all plants, are found in most environments except extremely arid or hot areas. C4 plants are adapted to hot, dry climates, and CAM plants are suited for even drier conditions. Each type has a different coping strategy for moisture-limited environments.

More about Early Human Migration

  • Mizmareck via Flickr
  • Aarhus University Research
  • Nature Communications Earth and Environment
  • Natural History Museum
  • Khan Academy
  • Biology Dictionary
  • Lex.dk
  • Milanković Cycles Explained

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Lily R December 26, 2023 - 1:32 pm

Good stuff but there were a few typos in there, saw a couple of missing commas and a misspelled word somewhere in the middle, should probably proofread these more carefully.

Greg H December 26, 2023 - 2:03 pm

This is some solid research, but the article could use a bit more on how this impacts our understanding of human evolution, you know like a bigger picture view.

Sandra K December 26, 2023 - 8:52 pm

Loved how it connected climate changes with human migration, but there were some parts where the flow got a bit confusing, especially with all those scientific names and periods.

Dave M December 27, 2023 - 2:15 am

the part about the Sahara turning green was super cool, never thought about deserts that way before, but the article kinda dragged on a bit too long after that.

Mike Johnson December 27, 2023 - 8:58 am

Really interesting read, but felt like it was a bit too heavy on the scientific jargon? Could’ve used simpler terms for a broader audience I think.


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