294 



NA TURE 



[January 30, 1908 



whereas the stimulus of a particular use or injury may 

 not be received. If, however, the latter be received, 

 the acquirement arises just as inevitably as the innate 

 character. Thus if the child receives a like injury, it 

 reproduces the scar on its parent's nose as certainly as the 

 nose itself. If the nose is inborn and inherited, then the 

 scar is inborn and inherited in the same sense. 



Had the true nature of the distinction between innate 

 and acquired characters been realised, had it been realised 

 that the difference is one of stimuli, not of innateness or 

 inheritability, and that acquirements are just as much 

 products of evolution as innate characters, it is impossible 

 that the controversy as to the alleged " transmission " of 

 the former could have endured so long as it did. In effect, 

 it was maintained by Lamarckians that a character (e.g. 

 a scar) which the parent was able to acquire in a certain 

 way (as a reaction to injury) because a long course of 

 evolution had rendered such acquisition possible to the 

 members of his race is reproduced by the child in a 

 different category of characters, and in a way (as a 

 reaction to nutriment) that no member of his race had 

 ever acquired it before, and with which, therefore, evolu- 

 tion had nothing to do. An actual miracle was supposed 

 to happen, the miraculous nature of which was concealed 

 under a misuse of terms. 



At the present day the majority of biologists are apt 

 to regard " acquirements " as mere accidents, as things 

 inferior to and less worthy consideration than " inborn " 

 traits. Very little study has been given to the evolution 

 of the power of making acquirements, especially use- 

 acquirements, and hardly any attempt has been made to 

 ascertain in what proportions the " normal " individual 

 of any species is compounded respectively of innate and 

 acquired traits. Lloyd Morgan, Baldwin, and Osborn 

 have certainly dealt with this power under the name of 

 "plasticity." But plasticity is not the same as growth, 

 as development, and the fact that they have regarded 

 acquirements as useful to the species mainly as affording 

 time and opportunity for the evolution of corresponding 

 inborn traits indicates an adherence, even if only a 

 modified adherence, to the prevailing biological view. The 

 evidence seems clear that animals low in the scale of life 

 have little or no power of making use-acquirements, but 

 that this power increases as species are more highly placed 

 until in man the main difference between the infant and 

 the adult is due to the use-acquirements made by the 

 latter during development. The power of making use- 

 acquirements is present only in structures where it is 

 useful, and only to an extent that is useful. Great 

 adaptability is thus conferred on the individual, for 

 he develops only those traits which are useful to him in 

 his particular environment, and is burdened with no others. 

 We have a special name, memory, for the power of making 

 mental use-acquirements. Memory is nothing other than 

 the power or faculty of storing mental experiences, and so 

 adding to the mental growth. It is strictly analogous to 

 the faculty of storing physical experiences, and so adding 

 to the physical growth. Without memory there could be 

 feeling and (instinctive) emotion, but no thought, for the 

 materials of thought would be lacking. Animals low in 

 the scale of life appear to have little or no memory ; they 

 are guided more or less entirely by instinct. Man is 

 intelligent and adaptable because he has a memory. He 

 is the most intelligent of animals because he has the 

 largest faculty for storing experiences. Memory, the 

 power of learning, develops under the stimulus of nutri- 

 ment, but intelligence and reason develop under the 

 stimulus of use. They are amongst the contents of 

 memory. We learn to think and reason just as surely as 

 we learn the facts about which we think and reason. 

 Reason, therefore, is an " acquirement." 



Probably no problem in biology is of greater theoretical 

 interest than that of the evolution of the power of making 

 use-acquirements. Certainly no problem is of nearly such 

 practical importance as that of determining the extent to 

 which the individual develops, on the one hand, under the 

 stimulus of nutrition, and, on the other, under the stimulus 

 of use. From the times of Lamarck, Spencer, and 

 biologists have very generally assumed that use 



Ron 



tends to cause development 'in all the structures of all 

 animals, but that the amount of this modification is trivial. 



NO. 1996, VOL. yy] 



As a fact, use causes development in only some structures 

 in some animals, and the major part of the development 

 of the human being is due to it. If, for e.xample, 

 biologists had ascertained and were agreed as to the 

 amount of this development, we should know to what 

 extent races and generations of men differ " innately " 

 and to what extent by acquirement, and therefore what 

 effect could be produced by this or that system of mental 

 training. Educationists could then apply this knowledge 

 to the training of the young. At present the basis of bed- 

 rock fact is lacking, and biology is shorn of much of the 

 practical importance which is its right. 



I venture to write this letter in the hope of directing 

 attention to one, at least, of the great problems of biology 

 which are neglected under present fashions. Experiment 

 itself, for example, loses much of its value unless the 

 worker has clear and comprehensive notions concerning 

 the subject with which he deals. 



G. .Arciidall Reid. 



The Melanic Variety of the " Peppered Moth." 



Mr. Spicer asks (January i6, p. 247), among other 

 questions, " how does the ' peppered moth ' contrive to 

 appear in the black country hatched with sooty wings that 

 harmonise with the now smoke-stained bark whereon he 

 must rest? " His point, I conceive, is that the melanic 

 variety is due in some unexplained way to the inheritance 

 of acquired characters. 



If Mr. Spicer found that an actor whom he had seen 

 perform the part of Hamlet on Tuesday was cast for 

 Macbeth on the Wednesday, he would not necessarily, I 

 suppose, conclude that the actor had added the part of 

 Macbeth to his repertoire during the intervening time. 

 Now there is more than a possibility that the black colora- 

 tion of the variety Doubledayaria may in like manner be a 

 repertoire pattern of the " peppered moth " evolved in the 

 remote ages of the history of the species. The dark form 

 is not necessarily atavistic in the general acceptation of 

 the term, as it may only have been developed by some 

 stocks of the species in a more or less restricted portion 

 of its range, the stocks in question having reverted when 

 the factor that put a premium on blackness gave place to 

 the original conditions of their habitat. The facts of 

 mimicry prove that the germ plasm of the Lepidoptera can 

 carry more than one distinctive pattern, and the tempera- 

 ture experiments of Standfuss and Merrifield suggest that 

 such latency may extend over long periods of the insect's 

 history. 



Mr. Spicer has tacitly assumed that the variety is con- 

 fined to the black country, but this is by no means the 

 c.-ise. The dark form is, I believe, taken in the Black 

 Forest in Germany ; certainly it occurs in Denmark, and 

 records from our own southern counties are not wanting. 

 It is by no means uncommon in and round London, and 

 has been taken as far out as Brentwood and Bexley, both 

 of which are outside the smoke limit as regards soot- 

 stained bark. In the last-named district, my friend Mr. 

 Newman has taken melanic forms of several other Geo- 

 metriid moths in addition to var. Doubledayaria. 



There seems to be no doubt as to the increase of 

 melanism among the tree-resting species of Lepidoptera 

 in certain districts of England during the past fiftv years, 

 but this increase is apparent outside the actual smoke- 

 stained area, though not perhaps beyond the range of 

 darker bark owing to the destruction of the lichens — a 

 cause that may have operated locally on more than one 

 occasion during the life-history of the species quite 

 irrespective of a sooty civilisation. 



Apart from lichens, even a change in the species of trees 

 composing a forest might have a marked effect on the 

 cryptic coloration of the bark-resting species of moths in 

 the locality. Birch would favour a pale coloration ; oak, 

 cherry, and especially the thorns, a darker one ; beech, 

 with its dense shade and wide range of bark coloration, a 

 darker or lighter pattern, according to the dampness of 

 the situation and whether the particular species emerged 

 before or after its full leafage was attained. 



The time during which the dark form could have been 

 evolved from the normal coloration of the species by the 

 action, direct or otherwise, of smoke is less than a 



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