PRESIDENTIAL ADDRESS. 507 
at once sort the people according to their really unimportant resemblances. 
That is human nature. 
The terms ‘ convergence’ and ‘ parallelism’ are convenient if taken with a gene- 
rous pinch of salt. Some authors hold that these terms are but imperfect similes, 
because two originally different organs can never converge into ‘one identical 
point, still less can their owners whose acquired resemblance depresses the balance 
of all their other characters. For instance, no lizard can become a snake, in 
spite of ever so many additional snake-like acquisitions, each of which finds a 
parallel, an analogy in the snakes, Some zoologists therefore prefer contrasting 
only parallelism and divergence. A few examples may illustrate the justifica- 
tion of the three terms. If out of ten very similar black-haired people only two 
become white by the usual process, whilst the others retain their colour, then 
these two diverge from the rest; but they do not, by the acquisition of the same 
new feature, become more alike each other than they were before. Only with 
reference to the rest do they seem to liken as they pass from black through grey 
to white, our mental process being biased by the more and more emphasised 
difference from the majority. 
10 Ax Bx Cx DE F 
9 
8 
ws 
6 
5 
4 
3 
2 Ax Bx 
n 1A BCODEF 
Supposing A and B both acquire the character x and this continues 
through the next ten generations, while in the descendants of C the same 
character is invented in the tenth generation, and whilst the descendants of D, 
E F still remain unaltered. Then we should be strongly inclined, not only to 
key together Cs with AG and Be but take this case for one of con- 
vergence, although it is really one of parallelism. If it did not sound so con- 
tradictory it might be called parallel divergence. The inventors diverge from 
the majority in the same direction: Isotely. 
Third case.—Ten people, contemporaries, are alike but for the black or red 
hair. Black A turns white and Red E turns white, not through exactly identi- 
cal stages, since E will pass through a reddish grey tinge. But the result is 
that A and E become actually more like each other than they were before. 
They converge, although they have gone in for exactly the same divergence with 
reference to the majority. 
In all three cases the variations begin by divergence from the majority, but 
we can well imagine that all the members of an homogenous lot change ortho- 
genetically (this term has been translated into the far less expressive ‘ recti- 
grade’) in one direction, and if there be no lagging behind, they all reach 
precisely the same end. This would be a case of transmutation (true mutations 
in Waagen’s and Scott’s sense), producing new species without thereby increasing 
their number, whilst divergence always implies, at least potentially, increase of 
species, genera, families, &c. 
If for argument’s sake the mutations pass through the colours of the spectrum 
and if each colour be deemed sufficient to designate a species, then, if all the tenth 
generations have changed from green to yellow and those of the twentieth 
generation from yellow to red, the final number of species would be the same. 
And even if some lagged behind, or remained stationary, these epistatic species 
(Eimer) are produced by a process which is not the same as that of divergence 
or variation in the usual sense. 
The two primary factors of evolution are Environment and Heredity. 
Environment is absolutely inseparable from any existing organism, which there- 
fore must react (Adaptation) and at least some of these results gain enough 
momentum to be carried into the next generation (Heredity). 
