When did Homo erectus first leave Africa?-Guest post by Mekhi

Introduction

It is commonly thought that Homo erectus was the first human species to leave our home continent of Africa. Though there is some evidence of earlier migrations accomplished by other species, it is clear that Homo erectus was the first species to accomplish mass migrations throughout Eurasia. Homo erectus fossils have been uncovered from right outside of Africa in sites in the Middle East, and extending all the way into Asia, going into Indonesia and even as far as China. 

This begs a variety of questions, mainly, why did Homo erectus leave Africa, and when did these migrations begin? There are some early sites right outside of Africa that give a good idea of generally when this species first began migrating. The closest site outside of Africa that contains Homo erectus remains is ‘Ubeidiya, Jordan. This site contains great faunal and lithic assemblages, and most importantly, Homo erectus remains, including a left parietal bone, a lumbar vertebrae, and some dental remains.

Research on this site shows that during the Pleistocene, when Homo erectus was living there, this area resembled a steppe environment, with very large water bodies and woodlands, very different from the environments in Africa. It appears that Homo erectus began migrating due to environmental changes. This answers the question of why they left, but not necessarily when. Homo erectus at ‘Ubeidiya are about 1.5 million years old, but there is an even older site farther from Africa that is even older.

Out of Africa

Even as predicted by Charles Darwin, humans and our evolutionary lineage originated in Africa. This was originally thought by the fact that our two closest extant relatives, chimpanzees and gorillas, also live in Africa, but it is now backed up by more fossil and genetic evidence. The migrations of humans out of Africa is creatively referred to as “Out of Africa”. Throughout the history of our evolution, there have been many migrations, all of which seem to have been accomplished by multiple different species. 

‘Out of Africa 1’ refers to the migrations of Homo erectus throughout Eurasia, in which they migrated throughout Eurasia, especially in Asia, beginning roughly 2 million years ago. These migrations are often thought to be the first times humans left Africa, but there is potential evidence of earlier migrations done by a different species. 

Oldowan style stone tools have been found in Zarqa Valley, Jordan, just outside of geopolitical Africa, dating to 2.4 million years ago. This suggests an earlier migration of an earlier hominin, something similar to Homo habilis, soon after the evolution of the Homo genus. Other Oldowan style tools have also been found in China, dating to 2.1 million years ago.

 All of these tool sites date to before Homo erectus ever left Africa and are more primitive than Homo erectus, suggesting that earlier migrations of early Homo took place 2.4 million years ago. These migrations could explain the origins of other primitive hominin species outside of Africa, such as Homo floresiensis in the island of Flores, in Indonesia. 

The first mass migrations were accomplished later, by Homo erectus, first migrating into the middle east, in sites like ‘Ubeidiya at 1.5 million years ago, and in an even older site, known as Dmanisi, which contains the oldest fossil remains of Homo erectus outside, at 1.8 million years old. This site contains great information about the earliest migrations of Homo erectus, and has been heavily studied. With the new research done, we now have a great understanding of the humans that lived there and what their lives were like.

The Life and Ecology of Dmanisi

The Dmanisi site is a fossil cave site which was previously laid beneath a medieval city. Dmanisi has held lots of Pleistocene faunal remains that have been uncovered, including about 40 fossil hominin remains. These fossils, along with the modern life of this area, gives a good idea of what the world was like there about 2 million years ago. 

Many amphibian, reptile, and mammal remains have been found. Amphibian and reptile species which have been found here include the European green toad (Bufo viridis), Greek tortoises (Testudo graeca), the European green lizard (Lacerta viridis), and several species of snake in the genera Elaphe and Natrix. Because all of these species are extant and still around today at Dmanisi, they can still be studied, allowing for a greater understanding of the ecology, landscape, and climate of this area. 

By using the Mutual Climatic Range method (studying modern life to compare to prehistoric life), it has been shown that the climate at Dmanisi was warm and dry, similar to that of modern Mediterranean climates, though the average temperature was slightly warmer than it is today. The average rain levels were also slightly lower than it is today, except for in the winter. 

The paleofauna of Dmanisi also indicates that the landscape was arid, with semi deserts, Mediterranean forests, and rocky substrate with bushy areas. Research of small mammals from this site, such as shrews, hamsters, and pikas, shows that roughly 36.5% of this environment was open-dry habitat, 25.7% water edge, 21% rocky, 15.5% open-wet habitat, and 1.3% woodland. 

These mammals, along with other carnivoran mammals found at this site, would have provided a good meat source for the hominins living there, aiding in the transition to a more carnivorous diet in hominins. As hominin populations migrated into this area, they slowly adapted to the unique environment, which could explain the unique morphology they possessed. 

The Dmanisi Hominins

The fossil hominins from Dmanisi are the oldest, unquestionable, confirmed hominins outside of Africa. By using 40Ar/39Ar (Argon-Argon) dating, paleomagnetism, and paleontologic constraints, it has been determined that these hominins lived around 1.8-1.7 million years ago. Morphologically, they are very basal, resembling early Homo in many ways, but also resembling the later Asian Homo erectus.

They are currently placed in the species Homo erectus, but have been sometimes placed in a separate species, Homo georgicus, though this species name is not commonly accepted at this time. There is lots of variation between the different individuals at the site, especially in their mandibles, but they are similar enough in overall morphology and time to belong to the same population. Their jaws and crania seem to be dimorphic in size, which could represent possible sexual dimorphism in the population.

The hindlimb anatomy of these hominins was similar to that of modern humans, and would have been useful for hunting down prey by using persistence hunting. Dental microwear analysis of the teeth of these hominins shows that their diets were consistent with other migrating populations of Homo erectus. Their teeth also share several synapomorphies (evolutionary traits shared between two related lineages) with Australopithecus and early Homo, especially in size. 

The Dmanisi hominins would have used the rocky terrain they lived in to produce many Oldowan style stone tools, mainly using basalt and andesite as their two main blanks for these tools. Many cores, flakes, and rock debris have been found, showing that all stages of stone flaking were present. The stone knapping wasn’t very elaborate however, as most of the stones were unifacial rather than the intricate bifacial tools produced by later Homo erectus. 

The Dmanisi Specimens 

There are 5 cranial specimens from Dmanisi, and several associated mandibular specimens, along with many other post cranial elements. The first specimen is known as D2280.

D2280

This specimen is the first of 5 cranial specimens, and is also the largest. The specimen is only a skull cap, but still has lots of well preserved features. From these features, we can tell that this individual is a male. Significant traits found in this specimen include a large supraorbital torus (brow ridge), a strong angular torus at the back of the skull, and a cranial capacity of about 775 cc. 

D2282

This specimen is the second cranial specimen from Dmanisi, belonging to a young female. It is similarly incomplete to D2280, with the majority of the interorbital region (consisting of the eyes and nose) incomplete. The zygomatic and maxillary bones are complete however. The mastoid portions at the lower back of the skull are partially crushed but are still preserved. The mandibular specimen D211 is associated with the cranium. This specimen possessed a cranial capacity of about 650 cc. 

D2700 

The third cranial specimen, D2700, belonged to a subadult male with partially erupted back molars. This specimen has damage to the maxilla and zygomatic bones, and is missing some teeth, though other scattered teeth found in the site fit in the sockets well. The D2735 mandible is associated with this specimen. This specimen had a cranial capacity of about 600 cc. 

D3444

D3444 is the fourth, and perhaps the most important specimen out of the five, and has great implications for the sociality of the Dmanisi hominins. This specimen belonged to an elderly male who had naturally lost all of his teeth. In the associated D390 mandible, the canine teeth sockets hadn’t healed over, suggesting he kept those teeth. However the teeth sockets in the cranium had fully healed over, showing that he had survived for a good while after he lost them. There are a few ideas of how he could have survived this. He could have eaten plants, softer meat such as brain matter or bone marrow, but must have been in some way cared for by the other individuals, showing evidence of compassion and care early on in the species. This specimen had a cranial capacity of about 650 cc.

D4500

D4500 is the last cranial specimen, and seems to be the most unique and complete out of the five, belonging to an adult male. This specimen has a very large face, with squared maxilla similar to Homo habilis, but a very small brain and a face similar to Australopithecus. Its cranial capacity was about 546 cc. This specimen had very bar-like browridges, and very large teeth which appear to be worn down and infected. The D2600 mandible is associated with this specimen. 

Conclusion 

There is little question that humans evolved in Africa and later migrated out of it in several waves. Homo erectus is typically considered the first species to have done this, in an event referred to as ‘Out of Africa 1’, in which it traveled throughout Europe and Asia. Earlier migrations may have taken place, but none as drastic, widespread, and long lasting as what Homo erectus did. 

The earliest Homo erectus remains outside of Africa have been found in two main sites. The closest site to Africa is ‘Ubeidiya, at 1.5 million years ago, and even older but farther away, at Dmanisi. 

The Dmanisi hominins are very important for our understanding of our evolution. Not only do they show when humans migrated out of Africa, when we shifted to more carnivorous diets, but they show when we began caring for each other, which was very important for our sociality, compassion, and morality. 

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