334 NATURAL SELECTION [CH. 



has arisen from a single primaeval form of life, those complex 

 powers of reaction to the environment, and the structures 

 subserving them, which distinguish man from the primordial 

 speck of protoplasm, must, in a broad sense, be regarded as 

 * acquired characters,' and, unless such characters were herit- 

 able, we should not have advanced to-day beyond the uni- 

 cellular stage. This contention remains true even if we accept 

 the suggestion, which Bateson has recently made, that the course 

 of evolution may conceivably be represented by "an unpacking 

 of an original complex which contained within itself the whole 

 range of diversity which living things present." This striking, 

 and at first sight paradoxical, notion contains fundamentally 

 nothing new. Erasmus Darwin, for instance, who believed in 

 the origin of the whole animal and vegetable world from "one 

 living filament, which the great First Cause endued with ani- 

 mality," must have had in mind, as the essential attribute of this 

 primordial living stuff, its inherent potentiality of development. 

 Every evolutionist must suppose that, as the descendants of the 

 primaeval speck of protoplasm multiplied and advanced along 

 diverse lines of development, what they gained in specialisation 

 they lost in plasticity. In other words, while the original living 

 matter contained within itself the power of development in the 

 direction of any and every class of the organic world as we now 

 know it, one of its descendants which has gone far along the 

 path towards becoming, let us say, an Angiosperm or a Rodent, 

 has only done so by closing the gates upon itself in countless 

 other directions : it no longer retains the power of developing, 

 for instance, into a Bryophyte or a Bird. In this sense all evolu- 

 tion is accompanied by a succession of losses, and the highly 

 evolved descendant of the original "living filament" pays the 

 price of its specialisation in losing the power to develop in 

 countless other directions. A human analogy, though obviously 

 imperfect, may perhaps make this point clearer. The future of 

 a new-born infant presents a wide variety of possibilities. In one 

 case, for instance, he may contain within himself the powers 

 at this stage, necessarily, in a latent form for ultimately 



