Middle Pleistocene Humans
The Middle Pleistocene is a time period, from around 780-125kya. It's a critical period for human evolution, because it saw the end of the Erectines (well, most of them cough cough Homo floresiensis cough cough) around 500kya, and the origins of humans with fully modern features around 200kya. During this time period, there were a number of human populations, the most famous of which are the Neandertals of Europe and the Middle East. As we will discuss, the exact relationships between these Middle Pleistocene populations has been hotly debated for over a century, but the picture has come into much greater focus in recent years, with the addition of new genetic data.
The general pattern of what happened in the Middle Pleistocene is clear. By 780kya, the beginning of the Middle Pleistocene, there were Erectines all over the Old World (Asia, Europe, and Africa). They had originally evolved in sub-Saharan Africa, and probably East Africa in particular. During the Middle Pleistocene, multiple waves of more advanced hominins (or perhaps just their genes and traits) came out of sub-Saharan Africa and swamped or replaced the Erectines, except in some places, like islands of East Asia, where they were protected through isolation.
Fossils from this first "wave" of advanced features are given the species name Homo heidelbergensis, although some anthropologists would prefer to call these fossils Homo erectus, or even Homo sapiens. The exact classification is debatable, and there will be more on that in a later reading. What is most important to understand is that late Erectines are very, very similar to Middle Pleistocene humans. The last of wave of Middle Pleistocene humans to spread across the world were the Anatomically Modern Homo sapiens sapiens (AMH). In other words, us.
What’s going on in Africa to fuel this rapid evolution of derived traits? Africa was where we evolved, and as a result, that's where the human populations were the largest. Larger populations = more diversity = more scope for natural selection. Larger populations also breed more competition, and competition fuels the “arms race” of evolution, too, so that new adaptations will spread quickly if they offer a reproductive advantage.
The major question that has kept anthropologists arguing for decades is: to what extent are these waves of new traits representing the development of different species, or are these just different populations? In other words, was the spread of Homo heidelbergensis into Eurasia (where Erectines were living), similar to the spread of monkeys back in the Eocene? When monkeys spread, they out-competed the prosimians who were living in those environments, and the prosimians ended up in nocturnal niches, or extinct. Is that what happened to Erectines when Homo heidelbergensis arrived? Is that what happened to Homo heidelbergensis when the Neandertals arrived?
Or was the spread of Middle Pleistocene humans vaguely like the European colonization of the Americas? European colonization led to the death of 90-95% of the Indigenous peoples of the Americas, but there was extensive intermarriage or interbreeding, so that the people who live in the Americas today, particularly in Latin America, are frequently descendants of the pre-colonization Indigenous population. This colonial population turnover was the result of disease, warfare, rape, and slavery. We have no evidence for those types of behaviors in the Middle Pleistocene, however, the Erectines and the Middle Pleistocene human were far more biologically different from each other than Europeans and Native Americans. Could evolutionarily significant differences have allowed Homo heidelbergensis to out-compete 90-95% of all Erectines, but also pass down their genes through interbreeding?
Or were the Middle Pleistocene humans, like Homo heidelbergensis and the Neandertals, just developed Erectines, local populations throughout the Old World whose traits changed through time as advantageous traits were spread through gene flow?
Regardless of the scenario, it's unlikely that the Middle Pleistocene human populations were separate species, or that they were separate species from the Erectines. Paleontological research estimates it takes about 10 million years before two populations become reproductively isolated and are separate species. In fact, many researchers have suggested (all though, thank God, not tested!) that humans and chimpanzees might still be capable of producing viable, fertile offspring.
Traits of Middle Pleistocene Humans
These traits were found in all the species of Middle Pleistocene Humans:
Near-modern, modern, or bigger-than-modern brain size. (Fun fact: Neandertals actually had larger brains, on average, than modern humans!)
Smaller jaw and brow ridge than Erectines
More advanced technology than earlier species, with more variable and innovative tools
The tools made by Middle Pleistocene Humans in Europe and the Middle East are called Mousterian. Mousterian tools are more complex than earlier forms of technology, and they allow the tool makes to get more cutting edge out of each rock.
Middle Pleistocene Humans definitely used fire for cooking, warmth, and protection
They made clothing of skins to protect from the elements.
They were more dependent on technology than earlier species of humans, based on how much of it they made, and how much it varied across time and space.
Their diet focused on the hunting of very large and dangerous animals, like mammoths and elephants
They all appear to have had some symbolic abilities, although it was not necessarily used. These abilities include language use, religious thought, and art/adornment. More on that later.
Many of these differences were just a matter of degree, not of kind, from the Erectines. In many ways, the Middle Pleistocene Humans continued to be very much like the Erectines. Physically, they are the same from the neck down. In terms of behavior, they continue to have (we believe!) a more modern family structure, diet, and technological abilities.
Species of Middle Pleistocene Humans
Homo heidelbergensis
This species could also be classified as an Erectine.
Found in Africa and Europe. There are no uncontroversial finds of this species in Asia
Dates from 800-125kya
Known for its heavy brown ridge and long, low brain case
May be ancestral to the Neandertals
Homo sapiens neanderthalensis (sometimes called Homo neanderthalensis, but that is wrong)
Found in Europe and the Middle East
Dates from 130-20kya
Large, long, low brain case, large nose, stocky build
Many of the Neandertal's physical traits represent adaptations to cold climates (like the one in Europe during the Pleistocene)
Physically, they were rugged and tough. Their skeletons frequently show healed breaks.
Ancestral to modern humans in Europe
Denisovans
Denisovans are fossil remains from a site (Denisova) in Siberia. Although the remains do not look very different from those of a Neandertal, they produced a genetic sequence that shows they were a separate population. They were likely found throughout Asia, since their genetic material is found in modern Asian populations
Dates are uncertain, since there is so little fossil material, and much of what we know comes from modern genetic studies. The site of Denisova itself dates to around 40kya
Ancestral to modern humans in Asia and Australia
Anatomically Modern Homo sapiens sapiens (aka AMHss)
This topic will be covered more extensively in a later section, but the basic information is as follows:
First found in Africa, then spread throughout the Old World
Dates of the first AMHss are 200kya. They (we) are still around today.
The only truly unique characteristic of early AMHss is the chin. We were less rugged than Neandertals, mostly because we lacked the adaptations to cold climates
Ancestral to modern humans throughout the world