PRESENT PKOBLEMS IN EVOLUTION AND HEREDITY. 317 



we observe the liypi'rti()i)liy of adaptive oii;aiisaii(l atioi)hy of iiiadai)- 

 tive or useless organs. Thiscoiiiix'iisatingre-adjustmciit, whereby tiie 

 Slim of imti'itioii to any region remains the same (hiring- re-distribution 

 to its parts, may be called metatrophism. It is the " gerrymauder " i)rin- 

 ciple in nature. 



In practical investigation it is >'ery dithcult in many cases to deter- 

 mine whether an orgau is actually develo}»ing or degenerating at the 

 present time, although its variability or tendency to ]U'esent indi- 

 vidual anomalies indicates that some change is in ])rogress. I may 

 instance the highly variable peroneus tertius muscle (Wood). Tlie rise 

 or fall of organs is so constantly associated with tlieir degree of utility 

 that in each case the doubt can be removed by a careful analysis of the 

 greater oi' less actual service rendered by the i>art in (juestion. Apart 

 from tlu^ ({uestion of causation, it is a fixed principle tliat a. ]»art degen- 

 erating by disuse in each individual will also be found degenerating in 

 the lace. 



Degeneration is an extremely slo^v proc(\ss; botliinthe muscular and 

 skeletal systems we find oigans sf> far on the down grade that they are 

 meie pensioners of the body, drawing pa.\' (/. c.^ mitrition) for past hon- 

 orable services without performing any corresponding work — the plan- 

 taris and pabnaris muscles for exani])le. ( )f course an organ without a 

 function is a, disadvantage, so that the tinal duty of degeneration is to 

 restore the balance between structure and function, by placing it liors 

 df comhdt entirely. One symptom of decline is variability, in which the 

 organ seems to be (lemonstratiug its own uselessness by occasional 

 absence. As Humphrey remarks: "The muscles which are most fre- 

 quently absent by anomalies are in fact those which can disappear with 

 least inconvenience, eitlu^r because they can be re])laced by others or 

 because they play an altogether secondary role in the organism.'' The 

 stages downward are gradual ; the rudiment becomes variable as an 

 adult structure, then as a fcetal structure; the ])ercentage of absence 

 slowly increases until it re-ai)pears only as a reversion; linally the 

 part ceases even to revert and all record of it is lost. This long strug- 

 gle of the destructive power of degeneration, which you see is essen- 

 tially an adaptive factor, against the protecti\'e power of heredity is 

 the most striking feature of the law of repetition. (See Galton's simi- 

 lar princi))h' of regression in anthropology.) 



A careful study of our develoi)iug, degenerating, rudimental, and 

 reversional organs am])ly demonstrates that man is now in a state of 

 evolution hardly less lapid. I believe, than that which has jn'oduced 

 the modern horse from his small five-toed ancestor. As far as I can 

 see, the only reason why our <'voluti(m should be slower than that of 

 the ancient horse is the fre(|uent intermingling of races, which always 

 temls to resolve types which have spc('ialized into more generali/ed 

 types. Wherever the human sp(>cies has been isolated foi- a long jieriod 

 of time, divergence of character is very marked, as will be seen in some 

 of the races I refer to below. 



