Dutchman Eugene Dubois was the first scientist to deliberately look for the beings that existed between 'the apes and modern humans' .
He and many other scientists were convinced there was only one intermediate species and that it must exist only in the tropics because they felt that humanity was most closely related to Orangutans and Gibbons and these species are found only there.
Gibbons walk upright far more often and far more easily than do chimps for example.
But Darwin stuck to his counter intuitive conviction that humanity was closest to the knuckle-walking chimps and since the chimps live only in Africa, humanity must have emerged there first. (Again Darwin was eventually proven right !)
So determined was Dubois that he shifted careers and got himself posted to remote Dutch Indonesia.
In 1891, at Trinil on the island of Java, he did indeed discover very early humanity - the famous "Java Man", now known to be an (estimated 500,000 year old) example of Homo Erectus.
Homo Erectus lived throughout Africa and the warmer parts of Eurasia between 2 million years and 70,000 years ago.
By contrast our own species, the Homo Sapiens species, are seen as becoming modern (in anatomy and in behavior) only about 50,000 years ago.
The first claim is based on comparing the shape and heft of ancient and recent human skeletons from before, during and after that important 50,000 year divide.
Since the presence of ancient human skeletons "fossils" is absolutely key to claiming that a site once held humans, this is not a controversial argument - human bones are one of the most preserved and undisputed artifacts of early human life.
But human artifacts of cloth and leather, even paint on rock walls are rarely found intact from hundreds of thousands of years back.
So that means that one of the key problems about also claiming that people dead hundreds of thousands of years ago could hold abstract thoughts like we do today is that few abstractly thought out objects survive that long a period of time.
But artwork carved into stone, bone or ceramics is a rare form of abstract thought made visible as art that can survive the ages.
Seeking such art marks was thus - or rather it should have been thus - Job One for everyone seeking Early Man.
But that presumes that in the Age of Progress that anyone was eager to find out just how far back modern-human-like behavior had existed and that simply wasn't so.
Metaphor of Progress as abrupt ladder steps rather than gradual ramp
Humanity in the Age of Progress created the metaphor of a long ladder, rather than a long ramp, to describe how they imagined 'Progress' had proceeded upwards, throughout time, from the ancient simple stupid bacteria to the big complex smart civilized European male.
Ladders presume wide distinct ('clearcut' - to use a term much favoured by Howard Florey) gaps between each ladder step - rather than the infinitely gradual continuum of a ramp.
This allowed human elites in the Era of Progress to see what they wanted to see : wide yawning gaps between men and women, educated and uneducated, white and black, man and animals, man and ape, man and the stone age men.
Seeing a common humanity between Stone Age Man and modern Man might have forced Aryans to also see a common humanity with their Jewish neighbours.
So despite Dubois's specimen of extremely early man being an unique find for a very long time, it wasn't studied as intently as one might think.
In fact, most scientists dismissed it outright, sight unseen -- tending to feel it was a late model of ape or an early model of modern homo sapiens - not an intermediate stage human at all.
But if they had looked at all seriously at the relatively few mollusc shells left by these extremely rare early human remains, they would have seen clear and unusual marks that couldn't have been done by Nature or ape-like beings.
Very sophisticated tools and reasoning were used to open the shellfish without ruining the meat inside.
And abstract art marks were scratched on one shell.
Both of these were hidden ----- in plain view.
But it isn't ever enough for science to merely discover things - what unconscious preconceptions scientists bring to bear upon their discoveries hampers what they will see.
A hundred and twenty years later, a new generation of scientists looked at the same shellfish and finally saw the clearly visible tool marks and art marks.
Because they were open to the possibility that modern humans weren't in fact as unique as human hubris had long thought.
Because they were willing to at least ask if ancient humans might have had abstract thoughts.
One can at least wonder if the Holocaust would ever had happened if the Age of Progress had been open - 50 years before the Holocaust - to seeking to see if early Intermediate Man could possibly share a common humanity of abstract thought with such exalted Aryan philosophers like Hegel and Kant....