Chance evolution of intelligent life.
Here is an extraordinary image by Leonard Eisenberg showing the evolution of life on Earth in diagrammatic form. It breaks the web page format but here it is:
It took countless freak accidents of evolution across three billion years and five mass extinctions to produce one tiny twig on the "tree" that evolved into beings who can communicate, write, invent, discover and reason.
Wikipedia states: "The total number of non-bacterial and non-archaeal species in the world has been estimated at 8.7 million"
How certain can we be - even if life has evolved on other worlds - that intelligent life is inevitable amongst all those branches?
I've heard it said that because of the huge number of stars in the Milky Way galaxy, that there must be countless other civilizations.
I am not so sure about that.