For approximately 150-200,000 years, humans essentially lived like very smart animals, then fairly suddenly, about 10,000 years ago, we all seemed to have discovered agriculture and "civilization".. a few thousand years later we were all writing. I have never seen a decent, logical explanation for how all the populations of the Earth took this "great leap forward" at the same time-After 150-200,000 years, suddenly within about 1% of that time frame, there are cities everywhere from the Middle East, to China, to North and South America? Writing starting independently everywhere? For me, this is the most mysterious event in all of history-any ideas?
Hey! Your "other" question is already cluttered up with some high voltage discussion and nice arguments so, I thought I should post my answer here as it is more peaceful and calm here. I was wondering whether I should have posted my answer there?
Now, I'll try to make sense while talking about a topic that I know little about.
1- It all started with the arrival of the first bipedal- Australopithecus anamensis. (some might argue that it was Ardipithecus ramidus). Ok, the point is, as our ancestors started to learn to walk on two feet, they had some challenges to face as bipedalism reduced their speed considerably putting them at a clear disadvantage against their predators.
Now, as this problem was faced by all the hominids all over the world at the same time, it led to some parallel thoughts (and thus inventions and discoveries) all over the world e.g. building homes, making weapons and tools etc. (The stone tools were first made by the handy man i.e. Homo habilis and not Australopithecus).
This tool technology was spread by Homo ergaster as they migrated outside Africa.
2- Then, in the course of evolution, the early humans started to have a complex cultural lives and they grew emotionally, e.g. the Neanderthals (who aren't our direct ancestors) started to bury the dead.
3- As the homo species like homo erectus, homo Neanderthals, homo heidelbergenesis and ancient homo sapiens (Cro Magnon) made further advances in creativity and productivity, they all felt a natural need to pen down their thoughts. This led to the cave paintings and carvings. All of those paintings can be interpreted as diary entries as you may see that the paintings and carvings simply depict what the early men "did" i.e. hunting, using tools etc.
So, I guess it is understandable why the "pictorial-scripts" developed contemporarily to each other.
4- But the question still remains: Why were the origin of world's ancient scripts so contemporary to each other? I guess, as man found the pictorial depiction of thoughts and emotions more and more inconvenient and tedious due to the diverseness of thoughts and situations to be depicted, it started taking help of symbols. Perhaps, this behavior was so "human-like" that every sub-species of the homo sapiens followed this pattern of 'depicting thoughts symbolically' universally.
5- Another reason of this might be migration. Before the ancient civilizations like Inka, Mesopotamia, Egyptian etc. even came into existence, the early hominids led a nomadic life. According to the "Out of Africa Hypothesis", all the modern humans "Homo Sapiens" originated from Africa. Later, they migrated to Africa, Asia and Europe and formed groups.
So, I guess due to their similar ancestral origins, the human beings had a common problem solving approach and hence, attempted the problem of inconvenience of pictorial scripts in a nearly identical manner.
The scientific difference in the scripts can explain that they were devised on completely different grounds but, the approach was similar due to common origins and creative grounds.