768 LIGHT AND LIFE 



processes in the living world not to feel that we by now know all 

 the present potentialities of nature in this respect, let alone what 

 may have occurred in the past. In particular it seems reasonable to 

 believe that there was once a time when vision was not and a time 

 when photogeny was not. This implies that the first photoreceptive 

 pigment molecule and the first molecule capable of being put chemi- 

 cally into an excited state must have originated from pre-existing 

 types, not having these properties, that served and perhaps still serve 

 some unrelated biological structure or function. Bioluminescence, 

 in fact, must be presumed to have arisen separately from several 

 such precursors. 



As to the biologies of photogeny and light perception, the only 

 dogmatic statements that can be made were made long ago, and little 

 new has been added except as possibilities. In a tentative way it can 

 be said that the burden of the evidence seems to be that species 

 vision evolved before species photogeny. There seem to be enigmatic 

 structural analogies between eyes and photophores, but it also looks 

 as if eyes and photophores must have arisen independently and under 

 quite different sorts of evolutionary pressures. In the case of eyes 

 it appears that the availability of environmental light has been a 

 powerful inducing pressure for the selection, or perhaps even induc- 

 tion, of photosensitive systems — that is, that light presents an oppor- 

 tunity for or creates a need for a particular ability (vision) . In 

 photogeny, on the other hand, it seems that the ability (light-produc- 

 tion) appeared first, and was then turned to use in conjunction with 

 vision — that is, uses were created in response to a fortuitous endogen- 

 ous ability rather than to environmental pressures. 



One salient and somehow disturbing feature of bioluminescence 

 is its accidental and incidental nature. Not only can it depend, at 

 least in bacteria and fungi, on a single gene mutation (13), but it 

 seemingly confers neither advantage nor disadvantage on many or- 

 ganisms in respect to survival, growth, nutrition, social relations, or 

 metabolic potentialities. Perhaps we are again yielding here to Dr. 

 Arnold's "disbelief in biolight" if we find difficulty in reconciling our- 

 selves to energy simply being thrown away as light instead of as heat. 

 However, we are on slightly more secure ground if we balk at the 

 apparently casual occurrence and significance of light production in 

 so many organisms, because we do know that in general few things 

 persist during evolution unless they confer selective advantage. Proba- 

 bly this simply means that biologists need to look harder at organisms, 

 and this is particularly apparent in reference to the deep-sea creatures 



