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Horse。 Where the Ass is the male； as in the case of the Mule； you find
that the head is like that of the Ass； that the ears are long； the tail
is tufted at the end； the feet are small； and the voice is an
unmistakable bray； these are all points of similarity to the Ass； but；
on the other hand； the barrel of the body and the cut of the neck are
much more like those of the Mare。 Then； if you look at the Hinny；the
result of the union of the Stallion and the she…Ass； then you find it is
the Horse that has the predominance； that the head is more like that of
the Horse； the ears are shorter； the legs coarser； and the type is
altogether altered； while the voice； instead of being a bray； is the
ordinary neigh of the Horse。 Here； you see； is a most curious thing：
you take exactly the same elements； Ass and Horse； but you combine the
sexes in a different manner； and the result is modified accordingly。
You have in this case； however； a result which is not general and
universalthere is usually an important preponderance； but not always
on the same side。
Here； then； is one intelligible； and； perhaps； necessary cause of
variation： the fact； that there are two sexes sharing in the production
of the offspring； and that the share taken by each is different and
variable； not only for each combination； but also for different members
of the same family。
Secondly； there is a variation； to a certain extentthough； in all
probability； the influence of this cause has been very much
exaggeratedbut there is no doubt that variation is produced； to a
certain extent； by what are commonly known as external conditions；such
as temperature； food； warmth； and moisture。 In the long run； every
variation depends； in some sense； upon external conditions； seeing that
everything has a cause of its own。 I use the term 〃external
conditions〃 now in the sense in which it is ordinarily employed： certain
it is； that external conditions have a definite effect。 You may take a
plant which has single flowers； and by dealing with the soil； and
nourishment； and so on； you may by…and…by convert single flowers into
double flowers； and make thorns shoot out into branches。 You may
thicken or make various modifications in the shape of the fruit。 In
animals； too； you may produce analogous changes in this way； as in the
case of that deep bronze colour which persons rarely lose after having
passed any length of time in tropical countries。 You may also alter
the development of the muscles very much； by dint of training； all the
world knows that exercise has a great effect in this way； we always
expect to find the arm of a blacksmith hard and wiry； and possessing a
large development of the brachial muscles。 No doubt training； which is
one of the forms of external conditions； converts what are originally
only instructions； teachings； into habits； or； in other words； into
organizations； to a great extent； but this second cause of variation
cannot be considered to be by any means a large one。 The third cause
that I have to mention； however； is a very extensive one。 It is one
that； for want of a better name； has been called 〃spontaneous
variation；〃 which means that when we do not know anything about the
cause of phenomena； we call it spontaneous。 In the orderly chain of
causes and effects in this world； there are very few things of which it
can be said with truth that they are spontaneous。 Certainly not in
these physical matters；in these there is nothing of the
kind；everything depends on previous conditions。 But when we cannot
trace the cause of phenomena； we call them spontaneous。
Of these variations； multitudinous as they are； but little is known with
perfect accuracy。 I will mention to you some two or three cases；
because they are very remarkable in themselves； and also because I
shall want to use them afterwards。 Reaumur； a famous French naturalist；
a great many years ago； in an essay which he wrote upon the art of
hatching chickens；which was indeed a very curious essay；had
occasion to speak of variations and monstrosities。 One very remarkable
case had come under his notice of a variation in the form of a human
member； in the person of a Maltese； of the name of Gratio Kelleia； who
was born with six fingers upon each hand； and the like number of toes
to each of his feet。 That was a case of spontaneous variation。 Nobody
knows why he was born with that number of fingers and toes； and as we
don't know； we call it a case of 〃spontaneous〃 variation。 There is
another remarkable case also。 I select these； because they happen to
have been observed and noted very carefully at the time。 It frequently
happens that a variation occurs； but the persons who notice it do not
take any care in noting down the particulars； until at length； when
inquiries come to be made； the exact circumstances are forgotten； and
hence； multitudinous as may be such 〃spontaneous〃 variations； it is
exceedingly difficult to get at the origin of them。
The second case is one of which you may find the whole details in the
〃Philosophical Transactions〃 for the year 1813； in a paper communicated
by Colonel Humphrey to the President of the Royal Society；〃On a new
Variety in the Breed of Sheep；〃 giving an account of a very remarkable
breed of sheep； which at one time was well known in the northern states
of America； and which went by the name of the Ancon or the Otter breed
of sheep。 In the year 1791； there was a farmer of the name of Seth
Wright in Massachusetts； who had a flock of sheep； consisting of a ram
and； I think； of some twelve or thirteen ewes。 Of this flock of ewes；
one at the breeding…time bore a lamb which was very singularly formed；
it had a very long body； very short legs； and those legs were bowed！ I
will tell you by…and…by how this singular variation in the breed of
sheep came to be noted； and to have the prominence that it now has。 For
the present； I mention only these two cases； but the extent of variation
in the breed of animals is perfectly obvious to any one who has studied
natural history with ordinary attention； or to any person who compares
animals with others of the same kind。 It is strictly true that there
are never any two specimens which are exactly alike； however similar；
they will always differ in some certain particular。
Now let us go back to Atavism；to the hereditary tendency I spoke of。
What will come of a variation when you breed from it； when Atavism
comes； if I may say so； to intersect variation？ The two cases of which
I have mentioned the history； give a most excellent illustration of
what occurs。 Gratio Kelleia； the Maltese； married when he was
twenty…two years of age； and； as I suppose there were no six…fingered
ladies in Malta； he married an ordinary five…fingered person。 The
result of that marriage was four children； the first； who was christened
Salvator； had six fingers and six toes； like his father； the second was
George； who had five fingers and toes； but one of them was deformed；
showing a tendency to variation； the third was Andre； he had five
fingers and five toes； quite perfect； the fourth was a girl； Marie； she
had five fingers and five toes； but h