"For the first 2 billion years or so , the rate of increase in complexity (of DNA) must have been of the order of one bit of information every hundred years. The rate of increase of DNA complexity gradually rose to about one bit a year over the last few million years.
But then, about six or eight thousand years ago, a major new development occurred. We developed written language.
This meant that information could be passed on from one generation to the next without having to wait for the very slow process of random mutations and natural selection to code it into the DNA sequence."
Stephen Hawking is trying to say that evolution - because of this development - has just become a whole lot faster.
I love the guy's candor.
"Because we claim to be intelligent, though perhaps without much ground, we tend to see intelligence as an inevitable consequence of evolution. However one can question that. It is not clear that intelligence has much survival value. Bacteria do very well without intelligence and will survive us if our so-called intelligence causes us to wipe ourselves out in a nuclear war."
He also posited that advanced life-forms have already found us but are just chilling and looking at us. But then, if they are so advanced why have they not destroyed us - for example, we don't think twice before killing a bug. :D
I had a thought. What if there were more advanced life-forms but similar to what we might do in the future, they destroyed themselves some million years ago on Earth? May be they managed to destroy themselves so well that they left no trace of themselves or their subordinate beings...