Frank Drake? His formula is in essence
Number of intelligent civilizations per galaxy =
(rate of star formation per galaxy, per year, long ago)
X (probability that a given stellar system produces such a civilization)
x (lifetime of such a civilization)
You get to multiply out whatever factors you like in the "probability"
factor. Largest uncertainty, however, may well be in the last factor,
for lifetime.
> a gorilla named Coco (?) who had been taught sufficient language
Koko. Frances Patterson has a book and some articles out about her.
-- Jay Freeman, First Extropian Squirrel