The development of Homo sapiens……
Hola friends, in this post of scientific revelation we will talk about humans and how the long journey of evolution has shaped our species. How from the ape the development led us to homo sapiens “the wise man”. This post will be part of blog series dedicated to humans and our journey from the primitive era to this era of advances.
“The purpose of human life is to serve, and show compassion and the will to help others”. Albert Schweitzer
The span of Hominin history
To make thongs clearer, 13.7 billion years ago there was a big bang somewhere in nothingness. It had given birth to space, time, matter, energy, and physics. Approximately 5 billion years ago from the solar system galactic cloud, our sun had born. Sun had taken 99.9% mass and rest of the mass distributed among planets. As you know because of gravity planets started to revolve around the sun in orbits. Chunks and debris of space had turned into compacted planets. About 4.8 billion years ago earth came into the picture.
The onset of life had started 2 billion years ago with microorganism and the first hominin appeared probably 7 million years ago. The development of homo sapiens was a tricky process with lots of errors and trials. There were mix and separation of species for years to know which evolution works. The earliest candidates for hominins are Sahelanthropus tchadensis (7 mya), Orrorin tugenensis (6 mya), and Ardipithecus kadabba (5.8–5.2 mya). As you can see I am using Hominin instead of homo because the hominin group has other genera than homo.
Homo and Hominin
There is a difference between homo our genus and hominin. Hominin explains animals that are more similar to us than chimps. Homo is a part of the whole hominin group which also has other genus and species inside them. Other genus and species of hominin groups are different from Homo genus with more apes like features. On the other hand, the Homo genus with its famous members including Neanderthals and Homo erectus shared the same body structure, brains, and tools. They used to live in groups as a hunter-gatherer. They had sophisticated tools for hunting. Now let’s get in the past to understand other species and the mutation that eventually lead to us.
The earliest hominin species
Humans are closely related to chimpanzees. According to fossil studies, humans and chimps shared a common ancestor 7 million years ago. Approximately 7 million years ago first hominin sahelanthropus tchadensis evolved which had teeth smaller than other apes. Smaller teeth explain that their eating habits must have changed. Small compact teethes suggest nuts, fruits, and meat in the diet. Apes have sharp and long teeth that help them in chewing leaves and branches. 6.5 To 7 million years ago another species orrorin tugenesis lived in eastern Africa. It had thigh bone very similar to the human femur which suggested upright walking. The first fossil remains of orrorin tugenesis found in Kenya in 2003. It was dubbed “the millennium man”.
In eastern Africa itself, another fossil of Ardipithecus Kadabba was found. It lived there 6.3 million years ago. The fossilized toe bone suggests bipedalism (walking on two legs). Out of all characters of a modern human, this is one distinct feature that is unique to humanity. Bipedalism serves as a key feature for archaeologists to put any primitive human fossil into homo or another hominin genera.
Although we would be able to walk upright, our ability to walk on trees were still intact. Around 4 million years ago lived another species of hominin Australopithecus anamensis that had lost its grasping feet used for tree walking. Multiple hominin species including Australopithecus afarensis and Australopithecus bahrelgazali lived around this time in eastern and central Africa. Sometimes there ranges may have overlapped like A. afarensis and Kenyanthropus platyops had overlapped territories. Archaeologists have found the fossil of Australopithecus africanus in southern Africa. A 3.5 million years old hominin Paranthropus aethiopicus was found in Ethiopia.
The onset of the homo genus
Around the same 2 million years ago time first and foremost member of our genus was found. Fossil of Homo habilis was found in Ethiopia with first tolls. They were either used for hunting or other purposes. Researchers have found remains of Homo erectus and Homo ergaster in western Asia and eastern Africa respectively. They are dated back to 2 million years old. Homo erectus probably has migrated out of Africa around this time. It had a human-like brain structure with an average 1,000 cc (546- 1,251 cc). We have found Homo neanderthalensis remains in Europe. They used to had larger brain than ours. Homo sapiens were evolved in eastern Africa around 200,000 to 150,000 years ago.
The theory of evolution
When Darwin had suggested that we have evolved from chimpanzee it created a lot of controversies. People used to think about human evolution in a very different way. Firstly, it was very difficult to accept that we are anyhow related to chimps and animals. We don’t like to associate ourselves with animal worlds. It took quite a long time to accept that we are the creation of evolution just like every animal. Secondly, when research started showing that first humans are likely to evolve in Africa, Europeans were very reluctant to accept it. Back then in the 18th and 19thcentuary social norms very different as Europe used to rule over the rest of the world.
Thirdly, when the theory that we have evolved from apes was accepted, scholars started looking for a missing link. Thinking back was focused on the fact that there had to be a human ancestor who would be intermediate between apes and humans. This ancestor would have a mix of human and ape body features. This all thinking had lead to the creation of whole new specie. This incidence is known in the scientific world as Piltdown man hoax and it is worth noting incident in human evolution and a blog post.
The Piltdown man hoax
In 1912 an archaeologist Charles Dawson contacted the British museum and presented them human skull fragments which he collected from Piltdown in England. After returning to the site they found some animal fossils and those helped them in determining the age of the fossil, 2.58 million years ago. They found a lower jaw on the site and its molar teeth were similar to humans. One sharp canine discovered resembles ape-like. This fossil human had a large brain and it was Eureka. A human ancestor Eoanthropus dawsoni, our missing link was found.
That time linear model of evolution was prominent thinking. One species lead to another and two consecutive species would have similar characteristics. That’s why it was thought that there has to be a human ancestor between humans and apes.
In 1891 and 1920 fossils of Homo erectus were discovered in Asia. They were dismissed because it had a small brain and small teeth, opposite of Piltdown man. When in 1924 a juvenile fossil of Australopithecus africanus was found it was also criticized. But these discoveries made scientists think about the authenticity of the Piltdown man. In 1930 during the study of the geography of Piltdown, geologists have found that sediments were deposited by Thames river. So how come an ancient fossil was found in modern sediments? After lots of investigation in 1950, it was concluded that Piltdown man is fake. Skull bones were only 600 years old and the Jaw was of Orrington.
Species of homo Genus
To understand our species tree we have to study when and how our genus separated itself from other hominins. It is a normal acceptance that the homo genus has developed from the Australopithecus genus. The first members of homo which have developed from Australopithecus were either Homo habilis or Homo erectus. There is an ongoing debate that who made firsts modern tools H. habilis or H. erectus. The oldest member of the homo genus is H. habilis which used to live in northern Africa from 2.4 to 1.5 years ago. Homo erectus was the first species who migrated out of Africa. We have found its earliest known fossil (1.8 million years old) in Damnisi, Georgia.
Upright man and Neanderthal man
The Homo erectus ranges comprise of Asia and the Middle East. They are also considered the most successful homo species that lived for 2 million years. Homo neanderthalensis also commonly called Neanderthals lived in Europe from Western Europe to as far as the middle east. They live from 2.6 to 11000 years ago. Fossil evidence suggested that Homo erectus were upright walkers as the name describe. They had a large brain with average 1000 cc very near to our brain. They had a large body with optimum muscle mass. Neanderthals had darkened skin which in later years turned fair. Neanderthals also had developed blue eyes and they were accustomed to living in harsh winters of Europe. The cranium capacity (cc) of their brain was 1500 cc.
Homo heidelbergensis was the last common ancestor between Homo sapiens and Neanderthals. They used to live in Africa and middle Eurasia some 700,000 to 300,000 years ago.
Homo floresiensis made a sensation when it discovered on Flores island of Indonesia. This species has a pet name “The Hobbit”.
The first partial body was of an adult female, LB-1. Other than her 11 individuals were found including tools and some animal bones. The fossil discovery happened from the same site Liang bua of the western side of the island. The species had members of just 1 to 1.5 meters heights with features in-between ape and hominin. This hominin brain size was equivalent to chimpanzee. It was very odd because other hominins who had primitive small brains used to live millions of years ago. How was it possible for a hominin of this early period to have such old primitive traits?
It is speculated that they were developed out of a group of Homo erectus which had stranded on the island. According to Foster’s rule mammals can change their size as per the availability of resources on the island. The small mammals get bigger and big mammals get smaller according to less food availability and fewer predators. There had been proof of this phenomenon ex. the channel island pigmy mammoth.
Other species in the development of homo sapiens
Some other species of Homo includes Homo Naledi found in South Africa, at rising star cave, the cradle of humankind. This species had lived approximately 300,000 years ago. In Altai cave, Siberia Homo Denisova fossils were found. Studied shows they lived 200,000 years ago.
To read more about our lineage refer to post where did we come from? a post on human evolution.
Our family tree
For a long time, it was thinking that we are not part of any group of the animal kingdom. We don’t have relatives and cousins and parents but know fossils and DNA studies have proved that we also have a family to count on. The development of Homo sapiens has happened through a long line of lineage. We come under the Hominini tribe which also includes pan, the genus of the chimpanzee. Our sister tribe is Gorillini ex. gorilla and subfamily is homininae. Our family is Hominidae means great apes. It also includes the sister family Hylobatidae lesser apes. we belong to order primates.
The development of Bipedalism
Bipedalism is the trait-associated uniquely with humans as we are the only animal who walks on two legs. On the way to the development of homo sapiens, we have learned to walk on two legs a long time ago. Birds also walk on two legs but their anatomy is different from us because they have wings on forearms so our comparison cannot be done. Up until this time Bipedalism is the main trait that we look in species to include them as Hominin.
In 1978 a team of archaeologists led by Mary leaky found fossilized footprints in Latolli Tanzania. Those prints were found on volcanic ash. They were 3.6 million years old. They belong to Australopithecus afarensis and it can walk upright. This species had a very small brain and ape-like features. This discovery had contradicted the idea that our large brain has first developed. In 1994 fossil experts found keens and ankle joints of Australopithecus anamensis in Kenya. This species had lived 4.2 million to 3.9 million years ago and was an upright walker.
To go even further, fossil experts have found a 4.4 million years old partial human skeleton of Australopithecus Ramidus (pet name Ardi) in Ethiopia. She was very small only 1.2 meters tall. She had both human and ape-like features. Fossil evidence suggested that she could live among trees as well as on the ground.
The science behind upright walking
It is clear that a large brain developed a lot later and upright walking was present in a lot of other genera. We know that use of language and sophisticated tools for hunting are also hominin traits. But animals also possess. For instance animals like ape family and dolphins also use a wide variety of sounds for communication. Some members of the ape family have found using resources like stone or sticks for gathering food. But walking on two feet and balancing the body is something only humans can do.
In humans, femur angled in at the keens which make them closer to each other. That’s why when we walk there is almost no movement of hips. In ape and chimps knees are apart which enables them a walk with a lot of hip-swinging. Now the question arises that why upright walking developed in the first place? There must be something that had pushed our ancestors to opt for a very new method of locomotion. The most famous theory is the savannah hypothesis.
The savannah hypothesis
According to fossil evidence around 10 million years ago large parts of eastern and North Africa were covered in lush green forests. But then land in east Africa began to rise due to tectonic plate movements. Rising land had stooped the rain clouds from the Indian ocean. Rainfall in the region became less and rainforest turned into the savannah. In savannah, hominin had to walk a few km to get to another patch of trees so it was better to walk on two legs.
Some experts have criticized this idea. The fossil of Ardi has suggested that it was a skilled tree climber and a good upright walker. This proves that it had lived in a woody environment and still managed to evolved bipedalism. Some species who lived in a woody environment were bipedal. Probably we had learned upright walking among trees when we were roaming in forests.
And the research goes on…
We need time to discover how many species are out there. How interbreeding and co-surviving had paved the way for the development of us, homo sapiens. Studies have found 4% of Neanderthal DNA in some populations of Europe. In the same way, we have Denisova DNA in China and Korea. This had proved that there was occasional interbreeding between many co-living species. As the research and fossil searching goes on we will likely know more about how we have developed into homo sapiens.