yiinc 27, 1872] 



NATURE 



175 



special characteristic ; thus, to fix the ideas, suppose we are 

 speaking ahout a peculiar skin- nark in an animal. The pecu- 

 liarity in question maybe conceived (i) as purely personal, with- 

 out the concurrence nf any latent equivalents, (2) as personal 

 but conjoined with latent equivalents, anrl (3) as existent wholly 

 in a latent form. It can be shown that, in the first case, the 

 power of hereditary transmission is exceedingly feeble, for 

 notwithstanding some exceptions (as in the lost power of 

 flight in domestic birds), the efl'ects of the use and disuse 

 of limbs, and those of habit, are transmitted to posterity 

 in only a very slight de;:p-ee. Again, it can be fairly argued 

 that many classes of cases which seem .at first sight to fall 

 under case (i), that is, to be purely personal, and to prove 

 a larger hereditary influence than what I assign to it, do really 

 belong to case (2). Thus, when individuals born with a peculiar 

 mark are reputed to be the first of their race in whom it had ever 

 appeared, it would be hazardous in the extreme to argue that the 

 latent elements of that mark were wholly deficient in them. It 

 is very remarkable (1 was indebted for a knowledge of tliis fact , 

 to Mr. Tegetmeier) how nearly every bar or spot found in any 

 species of an animal in its wild st.ate may be bred into existence 

 in the domesticated variety of that species ; showing that the 

 elements of all these bars and spots are universally present in 

 all varieties of the species, though their manifestation may be 

 overborne and suppressed. We therefore see that the hereditary 

 influences of an animal with respect to any particular spot are, 

 I will not say in every case, but certainly on the average of many 

 cases, much more numerous than if that spot had been purely a 

 personal characteristic, without the concurrence of any latent 

 elements. Bearing this argument in mind, we shall more justly 

 estimate the import of the statistical evidence to be obtained 



from breeders of animals. I should judge from the impression 

 left by many scattered statistics that it is perfectly safe to afl^rm 

 that breeders, when they mate two animals, each having the 

 same unusual ch.aracteristi;, not through known hereditary trans- 

 mission, but by supposed variation, would consider themselves 

 fortunate if one quarter of the progeny inherited that quality. 

 Now these successful cases are, as I have shown, on the 

 average, the ]3roduce of parents having the peculiarity not only 

 in a personal, but also, to some degree, in a latent form. We 

 may therefore reasonably conclude that, had the latter portion 

 been non-existent, the ratio of successful cases would have been 

 materially diminished. 



I should demur on precisely the same grounds to objections 

 based on the fact of the transmission of quali'ies to gi'andchildren 

 being more frequent through children who possess those qualities 

 than through children who do not ; for I maintain that the per- 

 sonal manifestation is on the average, though it need not be so 

 in every case, a certain proof of the existence of some latent 

 elements. 



Having proved how sm.all is the power of hereditary trans- 

 mission of the personal elements, we can easily show how large 

 is the transmission of the purely latent elements, in the case (3) 

 by appealing to the well-known facts of reversion ; but into 

 these it is hardly necessary for me to enter at length. The gene- 

 ral and safe conclusion is that the contribution from the patent 

 elements is very much less than from the latent ones. 



If we now combine our results into a single diagram, show- 

 ing the fainter stream of heredity by italic lines, and indicating 

 those processes by asterisks (*) which were described at length 

 in the previous figure, we shall easily recognise the complexity 

 of hereditary problems. We see thSt parents are very indirectly 



Structureless 

 elements of 

 parent . . 



through " Class-"! ('which by 



Representation "[Embryonic ele-' lopment " (« 

 afford . . . .] merits . . X come . . 



Deve-I ("which by " Family'i 



be- J Adult elements ' Representation " ' 



' Residue " after^L^tent elementsfwWch by 

 the abstracted jjj embryo lopment 



elements are J [ come . 



■ J \ contribute to .j Structureless 



> elements of 

 ' ^^'^-iLatent eleme.itsf "''^.'^'^ ^y " Jf''?;! offspring. 

 ^*' ^^'\ in adult Representation J 



J m aault . .y contribute to .J 



Structureless ele- 

 ments of fa- 

 ther .... 



Structureless ele- 

 ments of mo- 

 ther . . . . 



Embryonic * Adult FA THER ' 



* Latent in 

 embryo 



■ Latent i 

 father 



adult 



Embryonic * Adult MOTHER * ' 



Latent in * Latent in adult * 

 embryo mother 



Structureless ele- 

 ments of off- 

 spring . . . 



and only partially related to their own children, and that there 

 are two lines of connection between them, the one of large and 

 the other of sm.iU relative importance. The former is a col- 

 lateral kinship and very distant, the parent being descended 

 through two stages (two asterisks) from a structureless source, 

 and the child (so far as that parent is concerned) through five 

 totally distinct stages from the same source. The other, but 

 unimportant line of connection, is direct, and connects the child 

 with the parent through two stages. We shall therefore wonder 

 that, notwithstanding the fact of^ an average resemblance between 

 parent and cliild, the amount of individual variation should not 

 be much greater than it is, until we h.ave realised how com- 

 plete must be the harmony between every variety .and its environ- 

 ments, in order that the variety should be permanent. 



We also infer from the diagram how near, and yet how sub- 

 ject to variation, is the kinship between the children of the same 

 parents ; for only two stages are required to trace back their de- 

 scent to a common origin, which, however, proceeds from four 

 separate streams of heredity, namely, the adult patent and latent 

 elemeits of each of the two parents. 



An approximate rotion of the nearest conceivable relationship 

 between a parent and his child may be gained by supposing an 

 um containing a great number of balls, marked in various ways, 

 and a handful to be drawn out of th'm at random as a sample. 

 This sample would represent the person of a parf nt. Let us now 

 suppose the sample to be examined, and a few h;inds'ul of new 

 balls to be marked according to the patterns of those found in 

 the sample, and to be thrown along with them back into the urn. 

 Now let the contents of another urn, representing the influences 

 of the other parent, to be mixed with those of the first. Lastly, 



1 ' Embryonic ' Adult OFFSPRING. 



suppose a second sample to be drawn out of the combined con- 

 tents of the two urns, to represent the offspring. There can be 

 no nearer connection justly conceived to subsist between the 

 parent and child than between the two samples ; on the contrary, 

 my diagram shows the relationship to be in reality much more 

 remote, and consisting of many consecutive stages, and therefore 

 hardly to be expressed by such simple chances. Whenever the 

 balls in the urns are much of the same pattern, the samples will 

 be alike, but not otherwise. The offspring of a mongrel stock 

 necessarily deviate in appearance from each other and from tluir 

 parent s. 



We cannot now fail to be impressed with the fallacy of rickon- 

 ing inheritance in the usual way, from parents to offspring, using 

 those words in their popular sense of visible personalities. The 

 span of the tree hereditary link connects, as I have already in- 

 sisted upon, not the parent with the offspring, but the primary 

 elements of the two, such as they existed in the newly impreg- 

 nated ova whence they were respectively developed. No valid 

 excuse can lie offered for not atten ling to t'lis fact, on the ground 

 of our ignorance of the variety an 1 propo tion.ate values of the 

 primary elements. We do not mend matters in the least, but we 

 gratuito isly aid concision to our ignomnce, by dealing with he- 

 reditary iacts on the plan of ordin.Try pedigrees — namely, from 

 the pers ns of he varents to ihose of their offspring. 



It will 'le observe i that, ow ng to the clearer idea we havenow 

 obtained of ihe meaning of kinship and of the consecutive phases 

 of the chain of life, the various causes of individual variation can 

 be ea-ily and surely sorted mto their proper places. I will men- 

 tion a few of them, merely as examples. 



In the segregation of the embryonic elements, if the structure- 



