I know people don’t like being grouped with monkeys.  However, purely biologically we are.  Our genus (Homo) have only had one species (Homo sapiens) since at least the end of the last ice age.  But the human is placed in the family of great apes (Hominidae).  It consist a family in the order of monkeys (Primates).  Maybe people dislike monkeys just because they resemble us?  One speaks about the uncanny valley between something entirely human and something vaguely human-shaped.  People tend to react negatively to things which can be placed there.

How many species have existed within the human genus?  Homo habilis and Homo erectus I consider different species.  In contrast Homo rudolfensis is doubtful.  (There is only one really good fossil of it.)  I don’t think Homo eregaster consist a species of its own.  If so it should be classified as a subspecies of Homo erectus.  Homo naledi was a species of its own although its origin is unclear.  Homo antecessor is more uncertain.  I count Homo rhodesisensis as Homo heidelbergensis.  This species gave rise to us, the Neanderthals and the Denisovans.  The last one mentioned is controversial since the evidence is mostly genetic.  Certainly there was a population which forerun us in Asia and rarely met Neanderthals.

Chimpanzees are in fact capable of walking on their hind legs.  But this is uncomfortable for them.  Wild chimpanzees don’t do this more than they find necessary.  Their locomotor system is a compromise between swinging trees and walking on all fours on the ground.  Gorillas usually move on all fours on the ground and can rise on their hind legs.  For efficiently swinging trees they are too heavy.  Orang-utans can also walk on two legs and move their legs differently.  However, they are primarily adapted to swinging trees.

The evolution of human bipedalism started with sexual selection.  This was 5 – 6 million years ago in the African jungle.  One species of great ape divided itself in two populations.  The one where the males fought about the females gave rise to the chimpanzee genus (Pan).  The one where the males offered the females food gave rise to the genus Ardipithecus.  Such behaviour makes it an advantage to be better at walking on one’s hind legs.  Then they can carry the food in their hands.  It gave this population a lead in adapting to a drier climate.  But Ardipithecus lived in forest and possibly open woods.

4.5 million years ago the genus Australopithecus arose.  Its members moved on the ground at least as much as in the trees.  On the ground they walked on two legs with and orang-utan like gait.  In contrast they are now considered to have held their torsos upright.  All species were shorter than any present-day human population.  This could be explained as an adaption to an environment where their food was not as abundant.  I think they lived in open woods or savannah with scattered trees.  Not only did they eat fruit, leaves and herbs.  They ate root vegetables, nuts and seeds too.  Also, various smaller animals must have been included in the diet.  (Present-day chimpanzees can’t kill animals their own size.)  Early species had brains the size of a chimpanzee’s.  Later species evolved brains which were a little larger.  This pawed way for the human genus.

Opinions are divided on when the human genus arose.  Certainly Homo habilis arose at least 2.3 million years ago.  This species moved in the same way as present-day humans.  In contrast it was shorter with proportionally shorter legs.  It was still fur-covered like present-day chimpanzees.  Homo habilis did not live in trees but on the ground in open landscapes.  In the more open and dry environment they had to cooperate to get enough food.  This required a larger brain to know all group members.  The brain was at least 37% of a present-day human brain.  Yaws and teeth were now smaller but the nose was still ape like.  This species was definitely capable of making stone tools.  Some rock types can be cracked by banging on them.  Then one gets a sharp edge usable for cutting with.  Such were used to cut meat stolen form larger carnivores.  They could be used to reach brains and bone marrow too.  Leaves and herbs were no longer eaten in any larger amounts.  On the other hand fish was included in their diet.

Around 2 million years ago Homo erectus arose.  Their body proportions were comparable to present-day humans.  The species had not much more fur than the hairiest population today.  Both this and longer legs were adaptations to long-distance running.  Not having that much fur makes cooling off easier.  It was mostly their head anatomy which differed from us.  Their skulls were much lower with gigantic brow ridge.  The nose was human like which decreased water loss through exhalation of air.  Yaws and teeth were tangibly larger than in present-day humans.  However, they were still smaller than in Homo habilis.

Homo erectus existed as a species for more than 1.8 million years.  Already from start it had a brain 2/3 as large as ours.  Their brain size increased gradually over time.  Towards the end their normal rage of variation overlapped the one for present-day humans.  Primarily the larger brain was used to cooperate with each other.  Apart from physical signs of a person getting help from others this is hard to gather from finds.  What we know is they made stone tools looking like broad daggers.  Such could be used to carve spears and digging sticks.  The species invented hunting of animals at least their own size.  Later fire was tamed which gave heat and frightened animals away.  This too enabled cooking decreasing the risk of infections.  Likely Homo erectus could stick two objects together.  The species definitely spread to large parts of Eurasia.  It has been found as far north as England and the Korean Peninsula.  To me it seams plausible that they made clothes out of leather.  Make a hole in the middle of an animal hide and you have a poncho.

Eventually the western subspecies evolved into the species Homo heidelbergensis.  It arose 700,000 years ago.  Skeletons have been found in Africa, West Asia and Europe.  There was not much anatomical difference between them and us.  Their skulls were a little lower and their yaws a little bigger.  Some were very muscular compared to present-day humans.  The species showed some signs of ability to be artistic.  The beginning of an artistic ability was passed on to those species which evolved from it.

Three different species arose 200 – 300 thousand years ago.  Two of these were the Neanderthals and the newly discovered Denisovans.  The Neanderthals (Homo neanderthalensis) we now know were adapted to a cold climate.  They were not only short but very muscular too.  I think the Denisovans (Homo denisova) were adapted to a plant-rich diet.  Please note that large grass blades have never been eaten by any human species.  Instead they were used as dental floss.

The current human species arose in Africa.  I have already explained here why the race concept is meaningless.  Differences between present-day populations are subtle compared to differences between earlier human species.  There may have been larger differences before the last ice age.  But at the peak of the last interglacial the climate of Africa was at its wettest.  In fact so wet the Sahara disappeared.  When vegetation covered the entire continent all populations came into contact with each other.  As such they got the chance to have children with each other.  Can they it will happen, endogamy or not.

In addition there was a genetic bottleneck near the beginning of the last ice age.  74,000 years ago the supervolcano Toba exploded.  The resulting global cooling went considerably faster than usual.  Then I mean years instead of decades.  We know that several large animal species were drastically reduced in number at the time.  These include great apes, tiger and cheetah.  At most 26.000 of us survived, all in Sub-Saharan Africa.  These have largely given rise to the present-day humanity.  It became the species that changed the world!

 

Uploaded on the 27th of September 2024.