• All dates are approximate
• Based on recent scientific knowledge and theories
The evidence
 |
Sahelanthropus
tchadensis |
 |
| © Didier Descouens |
© Mateuszica |
| DATE |
About 7 million years ago |
| REGION |
Djurab desert of Chad |
| CHARATERISTICS |
Also known as «Toumaï», only a small cranium has been found.
Their brain was about the size of a chimpanzee's.
Some suggest they were bipeds. |
 |
Orrorin
tugenensis |
| © Lucius |
| DATE |
Between 6.2 and 5.6 million years ago |
| REGION |
Tugen hills of Kenya |
| CHARATERISTICS |
A few bones and teeth have been discovered.
Many think they walked upright because of grooves on the femur, but they conserved tree-climbing skills.
About the size of modern chimpanzees, they ate mostly fruits. |
 |
Ardipithecus
ramidus |
 |
| © T. Michael Keesey |
© Jason Sannar |
| DATE |
About 4.4 million years ago |
| REGION |
Middle Awash river valley, Ethiopia |
| CHARATERISTICS |
They walked on two feet, but they could still grasp with their big toe to climb.
They had reduced canine teeth.
Their brain was the size of a modern chimpanzee's. |
 |
Australopithecus
afarensis |
 |
| © Patrick Bürgler |
© 1997 |
| DATE |
Between 3.7 and 2.9 million years ago |
| CHARATERISTICS |
Known for their famous fossil «Lucy», they were slenderly built.
With smaller canines, their brain was relatively modest.
They were definitely bipedal, but the anatomy of their hands, feet and shoulder joints shows they were equally competent in the trees. |
 |
Paranthropus
boisei |
 |
| © Guérin Nicolas |
© Lillyundfreya |
| DATE |
Between 2.7 and 0.8 million years ago |
| CHARATERISTICS |
All Paranthropus species were bipedal and many lived at the same time as our own genus Homo.
They ate harder plant material and roots.
There are big differences between Paranthropus and Australopithecus skulls, the first are more massive and have a crest at the top like gorillas. |
 |
Homo
habilis |
 |
| © J-M Benito Álvarez |
© Lillyundfreya |
| DATE |
Between 2.3 and 1.4 million years ago |
| CHARATERISTICS |
They were short, with very long arms and a cranial capacity about half the size of modern humans.
They are known for the primitive stone tools they produced.
They walked bipedally, but retained an ape-like morphology. |
 |
Homo
ergaster |
 |
| © ? |
© flowcomm |
| DATE |
Between 2.2 and 1.5 million years ago |
| REGION |
Eastern and southern Africa |
| CHARATERISTICS |
They are thought to be direct ancestors of Homo sapiens.
They stood over six feet tall and used more diverse and sophisticated stone tools.
They walked like present-day humans and their big toe could not grasp anymore. |
 |
Homo
erectus |
 |
| © Thomas Roche |
© Ryan Somma |
| DATE |
Between 1,800,000 and 200,000 years ago |
| REGION |
Migrated to the Old World from Africa |
| CHARATERISTICS |
They were some of the earliest fossils discovered, so they were named «Upright man» before it was found that bipedalism had been going on for a long time.
They possibly lived in hunter-gatherer societies and were probably the first migrating humans.
They used primitive tools compared to Homo ergaster. |
 |
Homo
heidelbergensis |
 |
| © Ryan Somma |
© J-M Benito Álvarez |
| DATE |
Between 600,000 and 300,000 years ago |
| REGION |
Out of Africa and into Asia and Europe |
| CHARATERISTICS |
Their brain was almost as large as today's humans.
Recent findings suggest that they were right handed and that they buried their dead.
Their footprints show that their bone structure and gait were identical to modern humans. |
 |
Homo
neanderthalensis |
 |
| © ? |
© grapitix |
| DATE |
Between 500,000 and 22,000 years ago |
| REGION |
Europe, Western and Central Asia |
| CHARATERISTICS |
Recent studies (2010) suggest that there was some interbreeding with Homo sapiens sapiens.
The Neanderthal's brain size was comparable, if not larger than our own.
They were heavily built and much stronger than Homo sapiens.
Their diet was almost exclusively carnivorous. |
 |
Homo
floresiensis |
 |
| © Ryan Somma |
© Ryan Somma |
| DATE |
Between 200,000 and 12,000 years ago |
| REGION |
Island of Flores, Indonesia |
| CHARATERISTICS |
Discovered in 2002, they were nicknamed «hobbits».
Their extinction possibly occurred as recently as 12,000 years ago, so they probably lived along modern humans.
They had very small bodies and brains.
Some isolated groups may have survived up to a few centuries ago. |
 |
Homo
sapiens sapiens |
 |
| © ixo/Moa |
© Leonardo da Vinci |
| DATE |
From 200,000 years ago to now |
| REGION |
Originated in Africa |
| CHARATERISTICS |
Humans are the only remaining species of the Homo genus.
Humans have lost their strength during their evolution and are now proportionally 3 to 10 times weaker than the other great apes.
With a more erect posture, they are among the best long-distance runners of the animal world. |
What the names mean
Anthropopithecus or pithecanthrope? Early humans are considered as being half-human or half-monkey.
So Sahelanthropus means «Human from the Sahel region» and Australopithecus translates into «Southern ape».
Scientists only start calling them real «humans» with the genus Homo, about 2.4 million years ago.
They group all the species above in Hominina.
Wasted diversity
When you look at the chart higher up, you can see that things started out with one species of humans, then diversified into over twenty species, just to return to a single species 7 million years later.
We can't even figure out the path our own race took through this adventure.
This is why I call them all «humans», even though some were quite different from us.
We know their fate, they have all disappeared except us, but they are still part of our own history.
They were all humans because
they all walked on two feet
A few years back, it was thought that becoming «bipeds» was a result of leaving the trees for the ground.
Called the «savannah theory», this hypothesis has been seriously challenged, but it is still present in scientific literature and popular culture.
Bipedalism was supposed to have evolved slowly and was needed to free the hands to carry things around.
But the most recent findings show that it came very early in our history, before the savannahs appeared.
In fact, bipedalism is now considered the first and most important trait that distinguishes humans from the other apes.
Humans haven't invented bipedalism
Our ancestors began walking on two feet about 7 million years ago, while some archosaurs started doing so about 240 million years before them.
Later, some bipedal theropod dinosaurs became the first birds, about 150 million years ago.
Birds are mainly known for their flying abilities, but they spend most of their time on the ground, walking on two feet.
Other theropod dinosaurs, like the tyrannosaurs, were also bipedal.
Bipedalism has evolved several times in archosaurs and four times in mammals, notably in kangaroos.
It then appears that changing from knuckle-walking to bipedalism would be the event that triggered our speciation.
This shift in behavior also seems to have taken place rapidly, at the very start of our history.
What could have caused such a change?
It seems to me that only external pressures, coming from their environment, would be sufficient to alter their conduct so drastically.
I don't think that bipedalism was much of a choice; it was the result of a series of events.
Apes can't swim
Most apes have a fear for water; some will drown in knee-deep ponds.
Others may feel confident enough to wade in shallow areas, but none are proficient swimmers, except humans.
This inability to cross water formations was crucial in their evolution, since it isolated some populations who went on to become different species.
For example, the formation of the Congo river (about1.5 million years ago) could have led to the speciation of the bonobos, now separated from their chimpanzee ancestors.
Chimpanzees stranded in a
flooded forest
The best logical reason to explain our sudden abandon of knuckle-walking is the absence of dry land for an extended period of time.
This could easily happen if a population found itself stranded in a newly inundated forest with no dry land to be seen for miles.
 |
| © Luiz Bento |
| How would chimpanzees survive to this? |
They would have to adapt very rapidly, but if this situation lasted for several generations, important physical and behavioral changes would occur.
They would have to wade bipedally to get from one tree to the other and finally learn how to swim.
Many people have suggested that water has played a role in our history; the most important proposal is called the «Aquatic ape hypothesis». It covers a whole range of aspects and I don't necessarily agree with many of these.
Of course, no traces of these events would remain, so they don't interest science.
Back to knuckle-walking?
No way!
After the water receded, our ancestors wouldn't return to walking on their knuckles again.
Putting their weight on them had become much too painful.
The skin on your knuckles is delicate
and not conceived to support your weight
We can wonder how and why knuckle-walking could have evolved in the first place.
The skin on each side of your hands is very
different and it is much thicker and harder on the palm side.
The first humans start walking
In the beginning, our chimpanzee-like first ancestors probably couldn't walk very well on two feet, but they spent most of their time up in the trees.
Bipedalism involved major transformations of the body; the big toe, for example, had to evolve from a grasping position to become aligned with the foot about 2.5 million years ago.
Some say this was the moment when humans stopped climbing up trees, but I disagree.
Those humans
may have spent their daytime on the ground, but they still needed the safety of the trees to sleep for 2 million years afterwards.
Compared to the rounded figure of a chimpanzee, bipedalism has caused a considerable straightening of our skeleton which is still incomplete when you look at people on the street.
Only one race of humans left
Bipedalism is also an instantly recognizable trait, making it possible to easily identify another human.
Did all those early humans congregate into a big family?
Judging by our history, it would rather seem that our ancestors promptly killed anything walking on two feet they would meet.
