🚀 go-pugleaf

Some speculations (what else is this thread, anyway?):


P(life | suitable planet) 
	~ 1  			(Check out recent evidence for multiple origins 
				of coding. The person who said the "organic
				soup" theory was dead because of improbability
				should learn about the theory, due to Manfred
				Eigen, of the origin of coding by heterocyclic
				catalysis. Generating the negentropy is not
				a severe theoretical problem, and if coding 
				actually had multiple origins it must have 
				been a cakewalk for nature, however badly
				we might explain it.)

P(multicellular life | life) 
	~ 0.5 			(Within the lifespan of a biosphere. 
				It might be lower. The estimate is based
				on nothing more than the fact that 
				multicellularity appeared roughly midway 
				through the main sequence lifespan of the 
				sun.)


P(smart life | multicellular life) 
	~ 0.01 	        	(Smart life means e.g. birds and mammals.
				Check out Bonner's book _The Evolution
				of Complexity_, which might put this at ~1.
				That may be a major overestimate, however: 
				there may be just one fundamental adaptation 
				-- vertebrate sociality -- which drives the 
				entire phyletic trend towards increasing 
				"smartness" (encephalization). If that basic 
				adaptation itself has a very low prior 
				probability, this one is an overestimate. No 
				similar phyletic trend apparently occurs 
				outside the vertebrates.

				The justification for the number is that it
				is roughly the inverse of the number of
				animal phyla, only one of which exhibits 
				encephalization.)

P(symbolic intelligence | smart life) 
        "1 e-12"               (Specifically human intelligence is no more
(really just some very small   likely than is the specific adaptation
 number)		       pattern of any other species. The fact that it 
			       may open a new adaptive zone *if reached*
			       is not relevant to its conditional 
			       probability, which has to do with how easy it
			       is to arrive at an adaptation (preadaptation),
			       not with how good it is to have it once it 
			       has been arrived at (fitness).  By contrast 
			       to symbolic intelligence consider, e.g. eyes, 
			       which have evolved independently many different
			       times. So has flight.
			      
			       There is also the Saganistic possibility 
			       that symbolic intelligence does *not* prove 
			       to be adaptive for very long: the evidence 
			       of its mounting effect on the biosphere 
			       makes this a more than abstruse possibility.)

It interests me that many physical scientists seem to think either that

Sagan: P(life) ~ 1 & P(radio telescopes | life) ~ 1 --> many civilizations

or that

Tipler: P(life) ~ 0 & P(radio telescopes | life) ~ 1 --> sparse civilizations

while virtually all evolutionary biologists seem to think that

Simpson: P(life) ~ 1 & P(radio telescopes | life) ~ 0 --> sparse civilizations.

See Stephan Gould's essay about this in _Bully for Bronotosaurus_, and also
see his book _Wonderful Life_ (which I understand has not been a favorite
of the Seti crowd). [Some of the strange Cambrian critters Gould discusses
in that book have recently been held to be fossilization artifacts 
-- hodgepodges of bits of other organisms -- or to be assignable to known 
groups after all.]

------------
Alan McGowen