The earliest known hominid was Sahelanthropus tchadensis, represented only by relatively few fossilised skull fragments, he is so ancient it isn’t clear whether he could truly be considered human at all. Fossils found in Chad, dated to around 7 million years old, may have belonged to a direct human ancestor, or more likely to a neighbouring branch of the ape family tree. This uncertainty is common until around 4 million years ago; many species are known only by partial skeletons and the relationships between them are often unclear. The Australopithecines may be the first group of hominids that we can be said to understand to any extent.
Around 3.5 million years ago, Australopithecus afarensis appeared in East Africa. Typified by the famous skeleton of ‘Lucy’, A. afarensiswalked bipedally all the time, no longer relying upon the arboreal lifestyle of her ancestors. Behaviourally, A. afarensis may have resembled modern humans more closely as well, with males guarding territories and females dispersing in adulthood.
The genus Australopithecus gave rise to two species which lived between 3 and 4 million years ago; A. garhi and A. africanus. Both species were slender bipeds found in Africa, however A. garhi was outlived by A. africanus, who is believed to have become the ancestor to modern humans. A. africanus had a larger brain than his ancestors, and also more human-like facial features, however his fingers still had curved fingers, a characteristic of more ancient tree-climbing apes.
Around this time, another branch sprouted from the hominid tree; Paranthropus, represented by three species in Africa between 2.7 and 1.2 million years ago. They were much more robustly built than their gracile Australopithecine ancestors, and are thought to have preferentially lived in forest rather than the grasslands. This branch of the hominid tree, however, eventually turned out to be a dead end.
As Paranthropus reign was coming to an end, a new genus was appearing in Africa: Homo. Around 2.3 million years ago,Homo habilis was roaming the plains of Africa, to be joined later by a second, more sophisticated Homo species: H. ergaster, about half a million years later. Traditionally, the overlap between these species was thought to be minimal and H. habilis was believed to be the ancestor of H. ergaster. However, recent evidence suggests that H. habilis was still alive until 1.4 million years ago, suggesting that they may in fact be sister-species, descended from a common ancestor.
Further phylogenetic confusion comes over the relationship between H. ergaster and a similar species called erectusfound only in Asia. It is now widely accepted that these two names represent members of a single species, forming two populations spread across two continents. The appearance of this population in Asia represents the first venture of man outside of his African home. H. ergastergave rise to several daughter species, including H. heidelbergensis(~700 KYA), H. neanderthalis(~ 200 KYA) and H. sapiens (~175 KYA).
The consensus view of human evolution is currently a two-phase movement out of Africa. Early human evolution occurred exclusively in Africa, with the first wave of migration occurring around 1.8 – 2 million years ago, where we have evidence for Homo erectus in the Mediterranean and Asia. Thus the vast majority of human evolution in the 7 million years ago since our divergence from a common ancestor with Chimpanzees occurred in Africa. It was during our African evolution that the hominid lineage began walking upright, discovered fire, and began developing early signs of art and culture.
After his evolution in Africa, Homo ergaster slowly divided into two parties; one stayed behind in Africa, whilst the other, composed of small bands of people, over many generations, moved into Europe and Asia. Although Homo erectus (or ergaster) arrived in Europe around 700,000 years ago, there is no evidence of permanent settlements for a further 200,000 years. Settlements appeared first in southern Europe, moving northwards only when the climate allowed it.
The band of H. ergaster that stayed in Africa evolved into Homo heidelbergensis, a brainy hominid who may have been the first species to bury his dead. H. heidelbergensis, like it’s ancestor H. ergaster slowly expanded into Europe, and there, around 300,000 years ago diverged into Homo H.neanderthalis. Those that remained in Africa evolved into Homo sapiens, and modern humans were born. Finally, Homo sapiens too moved into Europe where they met their sister species, Homo neanderthalis. Estimates for the exact timing of this migration range from around 125,000 to 60,000 years ago, but the existence of the migration and our decent from an Africa ancestor are supported by both molecular and fossil evidence.
Although the majority of evidence collected over the past few decades has strongly indicated East Africa as the cradle of humanity, more recent genetic research has suggested that modern humans may have evolved much further south, in the Kalahari Desert, around 60,000 years ago. Modern humans arrived in Europe through the Levant (an area encompassing modern day Lebanon, Syria, Jordan an Israel) and spread both east and west, arriving into the Mediterranean around 36,000 years ago. Here modern humans encountered and lived alongside Neandetherthals until their extinction about 30,000 years ago. The last Neanderthals are believed to have taken refuge in Gibraltar, the warmest part of their original range. Although it is not clear what caused their extinction, they were more severely affected by the glacial conditions than modern humans. Modern humans are believed to have out competed the Neanderthals, as opposed to earlier theories that there may have been direct conflict. Whether modern humans and Neanderthals engaged in romantic liaisons has been hotly debated. Fossil evidence is of little help, as the early modern humans that arrived in Europe were more robustly built and Neanderthal-like than their modern counterparts. Some recent genetic evidence suggests that there may have been periods of interbreeding between the two species.
Our picture of human evolution is still quite fuzzy. Unfortunately, many species, particularly the more ancient ones, are represented by only partial skeletons making attempts to deduce inter-relatedness, and physical characteristics more difficult. These species are also outside the range of DNA anaylsis, and genetic has only really be helpful for determining features of the most recent hominid species; H. neanderthalis and H. sapiens. DNA has been able to inform us more on early migration patterns, as the marks of migration are still visible in our own genome today. Human evolution, although primarily African, has been marked by frequent migrations into Europe and Asia, with various populations of early hominids persisting there for thousands of years. This lead to interaction between different hominid species when they met, and at times may have lead to conflict, competition and even inter-breeding. There is also some evidence that art, culture and tool traditions may have been exchanged between species. Eventually, however, H. sapiens prevailed both in Africa and Europe, and from there went on not only to conquer the rest of the world, but also to gain a greater control of his environment through animal domestication and farming.
Articles in this Series:
- Intro: What Makes Us Human?
- Part One: A Brief History
- Part Two: Intelligence and Language
- Part Three: Anatomical Adaptations
- Part Four: Culture and Faith
Want to Know More?
- Becoming Human (interactive timeline)
- Harari (2014) Sapiens: A Brief History of Humankind
- John Hawk’s Web Blog
- Berger (2010) Australopithecus sediba: A newspecies of Homo-like Australopithfrom South Africa
- Henshilwood (2002) Emergence of Modern Human Behavior:Middle Stone Age Engravings from South Africa
- Krause et al(2010) The complete mitochondrial DNA genome of an unknown hominin from Southern Siberia
- Neanderthals may have interbred with humans
- Pinhasi et al (2011) Revised age of late Neanderthal occupation and the end of the MiddlePaleolithic in the Northern Caucasus
- Ward, Kimbel and Johanson (2011) Complete Fourth Metatarsal and Arches in the Foot of Australopithecus afarensis
- New Research Confirms ‘Out of Africa’ Theory of Human Evolution
- Europeans less genetically diverse than Africans
- Massive Genetic Study Supports “Out of Africa” Theory
- Spassov et al (2012) A hominid tooth from Bulgaria: The last pre-human hominid of continental Europe
- Williamson et al (2007) Localizing recent adaptive evolution in the human genome, PLoS Genetics 3(6); 901 – 915
- Balter (2011) Did Neanderthals Linger in Russia’s Far North?
- Hill and Walsh (2005) Molecular Insights into Human Brain Evolution
- Human Lineage Through Time
- Spoor et al (2007) Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya. Nature, 448: 688 – 691
Featured image used under a creative commons licence from Wikimedia commons. Original image by Didier Descouens