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Date? 12 AUG 1977 1693=PDT

rrons Lederberg | AWS
Subject: The logic of biology, Dew~lr{_ &C ols fray

To? FEIGENBAUM ee

I enJoyed our conversation yesterday.

A Jot of my acientific life has heen spent tn asking about the congruence

of oossible vs, actual histories of evolution == even back to that first

auestion of why dontt bacteria use sexual reproduction ‘like all other organisms!
do, {Would any a=prior{ speculation about selfereproducing complexes have
elevated sex to the {importance we assign to it a vosterior{?}

I an Sending you a reprint, vou may have seen veforer which in a way shows
the futility Crather the inexhaustibility) of speculation about possible lives,
But the exercise (on Signs of Lifes in re exobiology) was still a useful ones

So I am moved now to think a bit more about a more systematic decision tree
to try to reoresent possible earthly lives, the nodes of which are
a, The relaxation of various assumptions generated from our empirical
knowledge of esobes {the converse of exobes, viz, existing taxonomy}

b, The predication of vartous assumptions in areas that are not very
heavily constrained nowr owing to imperfect knowledge of the details
of mechanism in varjous areas,

{lt would illustrate al} this to challenge you to give some representation of
the set of not~fundamentallysimpossible kinds of intelligence that ceuld be
represented in wet brains; or Silicon ones for that matter, You are free to
fix any assUmotions that don't contradict fundamental rules of nature,}

The computer can help here, not so much in imagining hypotheses, but jn heloing
to manage a rather cammplex contingency structure, checking orthogonality and
cansistencys and sa forth,

Senaratelv, IT wil] try to Justify why so much biological research IS comparative
== in large measure to try to find what rules CAN be substantiated about the
predictable vs, arbitrary mantfestations, And in my view, comparative biolagy
has to spend conSiderable effort in LOOKING FOR still undiscovered organisms
whose attributes would corroborate/refute the indicated rules,

This Perhaps {is most important for microbiologys where it is likely we are
fron from exhausting the total Space of natural evolution, and technically
cam go much further in artifical design and construction. With macrobes it

is nore difficult to work out details of mechanism, but more likely that we
already know about a Jarae oroportion of survivors of the evolutionary
machanism,

One point underlies all this discussion == it is mentioned, oerhaos not
emphatically enough in "Stans of Life's the one basic princiole of bioloay
is EVOLUTION, The rest js history! how things in fact worked out on earth,