Historical evidence does support that Humans are amazingly smart, and don't need outside help. How do I explain their science: research, testing, observation, problem solving, and intuition the same as we use today.
Humans were around for over 200000 years, and 50000 years ago look at the leaps that happen all around you everyday, those same kind of leaps had been happening and building since when we were australopithicenes 3900000 years ago by 50000 years ago we started to really put things together, between 10000 & 20000 we'd learned farming, and animal domestication. Our common knowledge base just kept building up and it continues to do. By 8000 Years ago we'd got into monumental architecture and astronomy. These aren't earthshaking changes in science its just yearly build up of a knowledge base that we use today and they applied to the extent that they could with what was available and useful same as us. To say we needed help outside from offworld is an insult to our species and our genetic cousins.
You want to know what happened that all this knowledge was lost: wars, natural disasters, and dictatorships. Much of the problem lies with what humans did in between 300 and 1600 AD and how it led to extensive damage to humanity's knowledge base. The Fall Of the Empires, The Crusades, The Inquisition and Burning Times, The Discovery and subsequent Destruction Of The New World, the fires in numerous libraries and courthouses. Archaeologist are still piecing together what the people before 300 knew. In point of fact some people are still puzzling over little bits and pieces of how we did things just in the last 300 years which I'm sure some people will chuck up to offworld help, I know a some loons are already caliming ET helped with the microchip and lasers. Its an insult to all the people who kept building and innovating the common knowledge base and an insult to our species and our cousins to keep on putting forward the ET hypothesis. Furthermore to have off-world help they'd need FTL technologies and Power technologies that they themselves would have to build from their own evolving common knowledge base, where did they get theirs, more off world help? Not to mention even with FTL and a parsec a day travel time it takes a long to get anyplace in this galaxy. Let me give you an example: Lets look at a typical long whaling voyage they took 8 years, lets say that our intrepid ETs will take 8 years getting here and 8 years getting home total 16 years. At what is considered possible at sublight speeds thats 50% SOL thats anything within 4 light years, basically Proxima centauri, at lightspeed anything within light years you can see the 26 nearest out to 11.7 lightyears http://www.astro.wisc.edu/~dolan/conste ... arest.html
have we found any planets in those, no. So then you have to go to the fictions of FTL at a parsec a day (about the speed of the original Battlestar Galactica and about Warp 9.9 in Star Trek Next Generation.) That will put everything within 9527.96 lightyears in range. This is a map of all the stars within 10000 light years, see all those white dots those are stars, now who ever ET is they have to find a pre-electricity using planet, AKA Eart, that has life but no signals indictating it out of all those white dots and all the planets orbiting them. Its a delusion to believe in the ET hypothesis regarding pre-electronic ages, you have to start at the Marconi signal of 1897 and work light years out from it which indicates the current planets in range are all within 112 light years of recieving that first signal http://www.solstation.com/stars.htm