Letter from Francis and Odile Crick to Fritz Lipmann
In his letter Crick considered the role of chance and the possibility of choice in evolution. The evolutionary phenomenon
to which Crick was referring was the symbiosis of microorganisms, as in the phagocytosis (the engulfing) of bacteria by prokaryotes,
primitive cells without a clearly defined nucleus.
Number of Image Pages:
1 (75,593 Bytes)
1976-06-25 (June 25, 1976)
Original Repository: Wellcome Library for the History and Understanding of Medicine. Francis Harry Compton Crick Papers
I was very surprised to get your letter as no rumour of your eye trouble had reached me, possibly because we have been abroad.
It must have been a horrible shock. I do hope it clears up completely. Odile had a corner of one retina detach itself a
few years ago but they put it back and now she can see almost normally.
About chance. I don't think there is any real difference between us except for the words we use. Evolution takes place
when chance events prove favourable and are thus selected for. There is little, if any difference, in principle, between
a point mutation and the first step in symbiosis. What I object to is your use of the word 'choice' (page 5). I
don't know what this means. I would prefer 'chance followed by natural selection'. The only 'choice'
the organism makes is by being able to multiply and survive better i.e. to leave more descendants. This is not what is usually
meant by choice. In short you give the impression that this process was in some way different from normal evolution (It was:
two things became joined together rather than one thing being changed, but I don't think that really makes it different)
and that I can't see. The host did not select the right prokaryote by inspection and then beckon it to step inside.
(That would be called 'choice'). It was chance that made the host phagocyte a suitable prokaryote. The event probably
happened many times but only the lucky favourable combination was preserved by natural selection. But perhaps you don't