In the previous posts, we talked about how hominins evolved and why they evolved in Africa. In this consecutive post around the same topic, we will discuss all the hominin evolved before us. Theses hominins from the bygone era had eventually given rise to Homo sapiens. With each genus and species, we saw the adaptation which sums up in us.
We are part of the great ape family.
We are ape but three distinct features separate us from other apes. Firstly, we have big brains that are 5 times more than our body size. These brains have enabled us to form complex societal structures, innovation, languages, and creativity. Secondly, we are the only ones in the ape family with bipedalism. We walk on two legs, unlike our chimpanzee cousins. Thirdly, we have free hands to make tools and other things. Because we have developed bipedalism we can use our free hands for tool making, hunting, foraging, and many more. To learn about the development of homo we have to get into the past where Hominins from the bygone era evolved.
The earliest hominins
The candidate for the earliest hominin is Sahelanthropus tchadensis (7–6.5mya). This is probably the first species after the great split. The great split happened when our lineage separated from chimps 7 million years ago. Genetic studies have proved that we and chimps had a common ancestor 7 million years ago. The second oldest fossil remain was of Orrorin tugenensis (6mya) which was found in east Africa. Ardipithecus kadabba was the third candidate found in South Africa 5.2 million years ago.
Australopithecines, Ardi, and bipedalism
The most important genus after Homo is Australopithecus. In 1924 Archaeologists had discovered a juvenile skull in Taung South Africa. It was a juvenile primate. This child represents Australopithecus africanus. This species had a small brain and human-like teeth. The archaeologists’ team led by Mary leaky had found fossilized footprints in Tanzania, East Africa. They were 3.6 years old. Laotoli footprints were made on volcanic ash. The rift valley of East Africa was very active in the past and volcanic eruptions were quite common. Experts think the footprints were made by Australopithecus afarensis. It was a species of Australopithecus with small chimps like brains. The world-famous example of this species is Lucy whose fossilized skeleton found in east Africa.
Australopithecus ananensis’ fossils that lived during the Plio-Pleistocene era 4.2–4.3mya ago were found in east Africa. The two leg bones including one femur tell that it was bipedal. In 1994 an excavation in Kenya led to the discovery of another fossil of ananensis. A partial keen and ankle joint was found which again directed towards bipedalism.
During 4.4mya another species lived in Ethiopian woodland. A partial skeleton of Ardipithecus ramidus was found during excavation. The female “Ardi” had 1.2 meters of height. Her toe bone was apart from the rest of the fingers which means she was a good climber but her legs were more human-like. Ardi was probably arboreal. She could live among trees and ground.
The origin of Bipedalism
All australopithecines and Ardi had bipedalism so it is certain that walking on two legs developed a long time ago. Now there are two hypotheses that explain how bipedalism developed. First is the savannah hypothesis which says that as a result of tectonic movement land in east Africa begun to rise. The appearance of rift valley and mountains had stopped the heavy rainfall in the region. Savannah grew and rainforest shrank which forced our ancestors to evolved bipedalism.
The other hypothesis suggests that bipedalism developed among trees. Ardi and orrorin tungenesis lived in a woody environment and they both walked on two feet. We can understand it on an evolution basis. There was high completion among trees and woodland. All the modern great ape species live in the same niche and compete for the same food source. Maybe the competition of space and food pushed hominin to look for another niche and they opt for walking on the ground.
The science behind early childbirth
We know that even around 5 million years ago we were walking on two legs. So the transition from four-legged walking to two-legged made immense anatomical changes in our body. Our toe bones came closer to the rest of the fingers and our feet size decreased. Our legs became longer and lean. The huge grasping fingers on hands also became smaller and sturdy. Our spinal cord linked with the brain at the base of the skull and this change must have developed with bipedalism. The pelvis started turning into bowl size. The hipbone became rounded and our hips narrowed. This last evolutionary change has made everything different for us. Bipedalism has made female hips narrower as well which made the baby delivery difficult.
As I have already said humans have a very big brain, almost 5 times the size of their body. When pelvis was getting smaller and more rounded it was very difficult to push the kids with big heads. With the ever-increasing size of brain females and children, mortality increased a lot. Females couldn’t push the big head of kids and probably had died during labor. So a child with smaller heads was favored by evolution. Now in this scenario kids would have born underdeveloped and mothers would have needed more social support for them. Maybe complex social structures developed because of this. It became a necessity to take help from other members of the group. Maybe this has led to family situations.
The societal structure and early birth
Our ancestors became pairs who then had kids and they need to live together for solid 13–14 years to take care of kids. After millions of years, we have evolved into a creature of monogamy. We are possessive of our kids and spouses and we don’t like someone else claims on them. Although there are some tribes and foragers out there who live in different societal rules. There is no nuclear family and pair system there and members can have a relation with anyone. But in general, we all have the same societal rules. We can see social structure in modern apes also. Their young ones also need care for a long time. This same thing could apply for ancestors but more elaborately. Our social structures have led to society, civilization, and cultures.
This section is inspired by Sapiens- a brief history of humankind. Needless to say, this book by Yuval Harari is amazing folks. Give it a try you will love it.
List of hominins
In this list, I have tried to list all the major hominins from the bygone era. These species have contributed to our development.
Australopithecus genus (oldest to youngest)
Australopithecus anamensis (4 mya)
Au. Afarensis (3.7–3 mya)
Au. Africanus (3 mya)
Au. Deyerimeda(3.5 mya)
Early hominins (oldest to youngest)
Sahelanthropus tchadensis (7.2 -6.7 mya)
Orrorin tugenesis (6–5.5 mya)
Ardipithecus ramidus (4.5 mya)
Ardipithecus kaddaba (6–5 mya)
Homo genus (oldest to youngest)
Homo habilis (2.7 -1.6 mya)
H. rhodesiensis (1.8–1.4 mya)
H. ergaster (1.8–1.6 mya)
The way to our big brains
All the australopithecine species had small chimpanzee sized brains so it is obvious that our signature brains developed in homo species. The first homo member was Homo habilis which was found in east Africa. It is commonly called handyman and thought to be the first to use tools.
We have found that Homo habilis had an omnivorous diet. They used to eat meat as well as plants and fruits. Before homo habilis our diet consisted of plant-based material. Homo habilis probably had eaten left out meat. There are many epic predators in modern Africa. Certainly back then it was choked full of them too. I don’t think so homo habilis would have created tools that they can use in hunt of large animals. Our best bet is that they use them for extracting whatever there is left in a carcass. The question arises that why they even went for meat?
The two prominent hypothesis
There are many possible explanations for this and the first one is related to the savannah hypothesis. When rift valley started to rise in east Africa and forests shrank, quality food material also disappeared. In the situation of heavy forests, they had fruits and nuts which replaced with low-quality grasses and shrubs. Maybe this scarcity of food pushed our ancestors towards meat. Another theory is that when we developed tools we could extract bone marrow from the carcass. Our ancestors thought it as a good food source. So maybe they have encountered bone marrow and meat just by surprise.
When we had a plant-based diet our canine teeth were more like chimps, sharp, and edgy. Our molar teethes were broad and well versed in chewing hard plant material. By adapting to a more meat-based diet our molars became more sturdy and small and canine grew smaller. Before we jump further into this let’s know different hominin species in various genera. Homo habilis has first used tools in the history of hominin. It gave them an occasional meat supply. It must have caused a few lives and stability of species. By the previous point, I mean that when our ancestors have first started to meat eat it was hard to digest. Their previous generation were all plant-eaters and switching the food source must have caused deaths and diseases. Slowly this acquired trait went into our gens. This new adaptation has kicked the development of big brains.
The lava flows and hominin evolution
Although, it is thought that we did not have access to cooked food until very later. Probably later species of homo genus like Homo erectus or hedilgerbernesis had started the fire. But there is another thinking regarding the consumption of cooked food. We have general thinking that hominins started using fires around 1 million years ago. But think about it for a second, Around 2 million years ago Homo erectus appeared who were very similar to us in body anatomy. They have bigger brains than their ancestors, smaller jaw muscles, and teethes. They could not chew hard plant material for hours because of smaller teeth. Their brains size doubled than of australopithecines so what was the energetic food source. Moreover, how before the onset of fire they had these adaptations. It is a guess that maybe they had access to fire long before.
Most of the species were found in East and South Africa. We have found most of the species in the rift valley and that’s why East Africa is called the cradle of humanity. Be it Lucy, laetoli footprints, or Ardi. Rift valley had many volcanic eruptions in the past. When lava had no place to go it was dumped in the ground. These dumping grounds must have been hot spots of heat and boiling water. They might be the places where these hominins evolved and we had access to cooked food. Laetoli footprints were found on volcanic ash. Fossils of Lucy and Ardi have been unearthed from places where lava flows were common.
In 2010 scientists found fossils of Au. Sediba in Malapa, South Africa. It is a member of the Australopithecus genus. In 2015 we also found Homo Naledi in the rising star system, South Africa. Sediba dated back to 1.98 million years ago and Naledi was 335,000–236,000 years old. What I am trying to say here that we don’t know which primitive homo or Australopithecus species evolved into later more developed hominins including us. Maybe one species did not give rise to later developed forms but they were the result of breeding among individuals of different species.
Our evolutionary tree has little holes in it. We don’t know that which species of australopithecine gad give rise to the homo genus. It was thought for a long time that Au. Sediba was the immediate ancestor of the homo genus. But the dating of fossil made clear that sediba appeared along with H. habilis. Now, researchers think that sediba does not have strong relationships with the Homo genus. The similar traits which we have found in it and homo were evolved separately because they lived in a similar environment.
South Africa- an evolutionary island
There is another reason which I want to discuss more. South Africa has a history of mammalian endemism. There are many species of mammals that are only found in South Africa. Climate change is a possible cause of this endemism. As climate change happened over thousands of years during the cold glacial period’s rainforests of central Africa changed into savannah grassland. This condition must have joined east African Ethiopian highlands all the way down to South Africa. In this situation, the widespread African mammals can roam into South Africa.
During the warm greenhouse period, central Africa turns into rainforests again. It not only prevented the mixing of species between both regions but it also gave an undisturbed condition for South African mammals. We have found fossils of Au. Africanus in south Africa. It can be the case that it was an endemic form of much wider Au. Afarensis. They both derived from the same population but then isolation had turn Africans into a different species. This same condition can apply to Au. Sediba and Homo Naledi. Maybe they separated from a larger population of north and developed into different species in the south. We can also think that these species of the south have no contribution to the development of the homo genus.
Homo genus(modern hominins from the bygone era)
I have already written a list of species in the homo genus. In this section, we will discuss them in little detail.
This fossil of an adult female LB-1 was discovered in liang bua Indonesia. We found this species on Flores island. It had a small brain and a body size of 1 meter. Many scientists think that it derived from a stranded population of Homo erectus. The fewer resources of the island had turned it in dwarf. The fossil dated back to 35k to 45k years ago which was a strikingly young age for very primordial features of this species.
Kabwe-1 fossil was unearthed in 1921 from Kabwe Zambia, during mining. A swiss miner has found the only skull fossils of this adult male. It resembles homo Erectus by low braincase and large brow ridges but it has more modern features related to modern humans. Its face bone shows more modern features and it had a large brain. Most scientists now include it under Homo heidelbergensis.
In 1908 researchers found another hominin species near Heidelberg, Germany. The fossilized mandible had few molar teeth and it was heavy. Further studies have shown that this species had large brow ridges, large braincase, and face more towards modern humans. It was a regular user of fire and hunted large games routinely. It lived during the middle Pleistocene from 700,000 to 300,000 years ago.
It lived around 1.9 to 1.8 million years ago in east Africa. Some experts think it was the morphological boundary between australopithecines and homo. The best-discovered fossil is KNM-ER 1470. Its discovery happened in 1972 and it had larger cranial capacity than Homo habilis. It also had a long face and long teethes.
This species lived during the lower paleolithic from 1.2 to 0.8 million years ago. These fossils are the oldest in western and central Europe. However, many think they are remains of heidelbergensis. We found their fossils in Spain between 1994–1996. These fossils of 6 individuals are different from other fossils because they have non-identical jaw and teeth.
This extinct species used to live in Africa during the early Pleistocene some 1.8 million years ago. Scientists have found most of its remains in east Africa. It had either evolved from h. habilis or H. rudolfensis. In 1984 scientists have uncovered a complete skeleton of Turkana boy from Turkana lake, Kenya. It had a bigger skull and a large brain than habilis. It also had a short face and a long nose.
This hominin species lived during the early Pleistocene 2.3 million years ago. The discovery of the first fossil happened in 1955 at Tanzania by anthropologist mary and Louis leaky. They also discovered the first tools in the same Olduvai Gorge. It had slightly bigger brian than australopithecines nad shorter molar teethes. The name means handyman.
This is one of the most successful hominin species and its origin dates back to 2 mya. It is also the first species that has migrated out of Africa. Its brain was big, almost double the size of previous species. It had a lean and tall body. Anatomically it looked very similar to modern humans. Its brow ridges were soft and had shorter molar teeth.
When our ancestors developing a new food habit of meat and an omnivorous diet a different genus branched out. Paranthropus genus had bigger jaw and sharp canine which suited to chewing of hard plant material. They lived between 2.6 to 0.6 million years ago along with our ancestors. The reason for their demise is not clear but it’s a common understanding that they didn’t adapt to changing climate. They were very used to African climate and especially food. Thye could not cope up with changing climate and died out.
In recent years we have a fair understanding of our origin and species before us. As research and excavation will go on we will discover more about The hominins from the bygone era…..