Two levels of information in DNA: relationship of Romanes' "intrinsic" variability of the reproductive system, and Bateson's "residue" to the species-dependent component of the base composition, (C+G)%.

In 1886 Charles Darwin's research associate George Romanes published a paper entitled "Physiological Selection: An Additional Suggestion on the Origin of Species". This was criticized by his Victorian contemporaries and largely ignored by those who followed. However, the recent recognition of two levels of information in DNA suggests that Romanes had solved the major problems with Darwin's theory. It was apparent from the outset that the form of reproductive isolation likely to apply most generally to initial species divergence (hybrid sterility), would depend on differences, not in "primary" information ("genic"), but in "secondary" information ("chromosomal"). This viewpoint, further elaborated by Bateson & Saunders (1902), White (1978), and King (1993), is criticized by the genic school (Coyne & Orr, 1998) because it requires visible differences between chromosomes, and appears not to explain Haldane's rule. However, chromosomal differentiation with respect to the species-dependent component of base composition [(C+G)%; Forsdyke, 1996] appears to resolve these problems. Because it explained so much, it was easy to believe that the genic viewpoint explained everything. Romanes and Bateson thought otherwise. We are only just beginning to recognize what they were trying to tell us. Copyright 1999 Academic Press.