Every so often scientific claims are made about the likelihood or otherwise of intelligent life evolving elsewhere in the universe, a recent example is this article:
Leaving aside the difficulty of making predictions based on a sample of 1, I have another issue with the assumptions made in some of these discussions, inlcuding the one above. Those who have concluded intelligent life is extremely unlikely to arise in the universe point out the number of improbable steps required. For instance the linked article states:
"Prof Watson suggests the number of evolutionary steps needed to create intelligent life, in the case of humans, is four. These probably include the emergence of single-celled bacteria, complex cells, specialized cells allowing complex life forms, and intelligent life with an established language.
“Complex life is separated from the simplest life forms by several very unlikely steps and therefore will be much less common. Intelligence is one step further, so it is much less common still,” said Prof Watson"
I'm not happy with this, especially the 4th step- I think once you have evolution acting on multicellular life forms then forms of marvellous complexity seem bound to occur and human culture is not less likely than termite mounds, chameleon camoflage or even lichen. It seems as though it is because the products of human culture are so undeniably unique. But the transition from australopithecus to homo, or heidelbergensis to sapiens is not a critical and necessary step in the way that prokaryote to eukaryote is. I rather think of the human brain like the peacock's tail, a flamboyantly elaborate structure produced by the engine of evolution.
Anyhow the case still stands that it took a long time to get from bugs to people. The critical step seems to be the "bugs/protists to jellyfish" one. That life could throw up something as wonderful in its way as a cyanobacteria at the very dawn of the earth and then just sit there, soaking up the sun for a couple of billion years is terrifying and humbling. Of course that couldn't really the case, clearly the global genome would have been dynamic throughout this period, perhaps many abortive pre-precambrians and proto-ediacarian events occurred without leaving traces.