Video 1:
Welcome to your third week of lab. This week you will learn about the origins of your own Genus, the Genus Homo. We will discuss the trajectory from Homo habilis to Neanderthals and modern Homo sapiens, and how different species in the Genus Homo migrated out of Africa at different points in time. We will specifically look at the origin of Homo sapiens in Africa, and how the migrants of this species reached far-away areas of the world, replacing and sometimes interbreeding with, prior species of the genus Homo living there, such as Neanderthals, Homo neanderthalensis.
We will then end by recapturing some of the things we know about human evolution, and a couple of the areas that are not yet settled.
Video 2:
Around two million years ago, a new hominid species occurred: the brain was slightly larger than any other species we have met this far, and the face and teeth were smaller. Here she is, Homo habilis, the first member of our genus Homo. It was thought that Homo habilis was the first species to make stone tools, hence the name which means handy man, or tool-maker. However, as we discussed last week, Australopithecines might have made stone tools. The first specimen of Homo habilis was discovered at Olduvai Gorge, Tanzania, by the famous archaeologists Mary and Louis Leakey. Homo habilis likely lived from 2.4 mya and lasting about a million years, overlapping with Australopithecines.
However, during this time another species appeared: Homo erectus. Now we have individuals with enlarged brain cases, and more modern body proportions. The first specimen of Homo erectus was found in China, in late 19th Century, before any of the African fossils were discovered. Homo erectus was likely the first of our ancestors to venture out of Africa as no earlier remains of Australopithecines, Ardipithecus or Homo habilis have been found outside Africa. There is much variation of the physical features of Homo erectus, and some scientists classify them into a range of different species. For our purpose, the term Homo erectus suffice but do note that books and articles might split Homo erectus into several other species, such as Homo heidelbergensis and Homo rudolfensies.
I. Now, let us look at a Homo erectus skull: Due to the small size, this is likely a female, from around 1.9 mya, Turkana Basin, Kenya. Notice the much reduced post-orbital constriction, the smaller eye sockets. Her teeth are reduced in size compared to the Australopiths, her fore-head is steeper and the
prognathism is reduced.
Video 3:
Neanderthals, Homo neanderthalensis, were first found in Europe. They likely evolved in colder climate from migrating Homo erectus, around 250.000 years ago. They are not the direct ancestors of Homo sapiens, but a closely related species. Homo sapiens originated in Africa much later, about 200.000 years ago, and when the first members of Homo sapiens ventured out of Africa they encountered Neanderthals in Middle East and Europe, replacing them at the end but also interbreeding.
The first specimen was discovered in 1856 in Neanderthal, Germany. They were adapted to colder climate with short, stocky build.
The skull has characteristic heavy and arching brow-ridges, and a large brain case. Some Neanderthals had larger brains than modern humans, but likely due to their larger body size. Notice how the skull is long and low, rather than high and rounded as on this Homo sapiens.
The nasal area is large, and the face is protruding below, called midfacial prognathism. A protruding bone on the back of the skull, called an occipital bun, is one of the identifying characteristics of classic Neanderthals and may even be found in some modern populations.
Video 4:
The modern version of our species species, Homo sapiens in its anatomically modern version, originated in Africa around 200.000-years ago. By around 35.000, Homo sapiens was the last hominid standing in the world.
Homo sapiens left Africa likely just before 100.000 years ago. In Middle East and Europe, they met Neanderthals.
Further east, towards Asia, they encountered other groups of hominids, such as the Denisovans who we still know little about. They were likely descendants of earlier Homo erectus migrations.
Characteristics of Homo sapiens are:
A: Chin
B: Elevated and rounded cranial vault. This has likely to do with reorganization of the brain.
C: Reduced face and prognathism, related to a general more slender build and different skull proportion.
D: Brow reduction - likely due to reduced muscles, slender build, and warmer climate.
G: Reduced dention, both molar and canines. It was much more pronounced when compared to earlier Hominids.
We have seen how this has changed several times depending upon diet specialization. Homo sapiens are omnivorous, and specialize culturally, this is to say we cook food.
H: Brain expansion
Video 5:
So what is it that drove the evolution of Homo sapiens and what are Homo sapiens characteristics?
The first characteristic is Bipedalism? Likely climate change and the opening of a niche of more Savannah habitat Less sexual dimorphism? Reduced competition among males for mates and/or other ways of solving disputes Slender skull and reduced ridges and crests? Compared to Neanderthals: climate change - they were specialized for cold weather.
Reduced teeth? Cooking, diet change, and change in social structure.
As you see, most likely not one thing drove human evolution. Rather, at different times, different adaptations were beneficial. They then created a new scenario for a new adaptation. So, when we talk human evolution, we need to be specific what time-frame (split from ape lineage or emergence of Homo sapiens) and what trait (bipedalism, brain expansion, language, etc).
We know that the human lineage split from the lineage leading to bonobos and chimpanzees 5-7 million years ago.
We know several hominin species lived at the same time in Africa and potentially other places in the world, from around 3 million year ago to at least 35.000 years ago, though additional fossil finds may push this date to become even more recent. By at least 2.5 million years ago, our ancestors made stone tools.
We are still not sure when language emerged and whether Neanderthals could speak. We are also discovering new fossil and genetic evidence for Homo sapiens encountering other Hominid species than Neanderthals when they ventured out of Africa, though exactly when, how, and who is not settled.
The topic of when we were able to control fire, for scaring off predators and cooking food is also hotly debated.
I encourage you to stay tuned to the news coming out regarding new fossil and DNA finds - it is an incredibly exciting time for the topic of human evolution and we are constantly gaining new knowledge about our ancestors and our own past.