Thomas de Quincey - "The Notebook of an English Opium Eater"

Bertrand Russell - "The Problems of Philosophy"

Catherine Parr Traill - "In The Forest"

Ambrose Bierce - "The Parenticide Club"

New Philadelphia Book Publisher Highlights Local Talent
Book and Publishing News from Publishers Newswire(tm)

Looking for Child to be on Cover of a New Book, 'The Model Child'
PHILADELPHIA, Pa. -- The Philadelphia literary world will celebrate the launch of two new players today, April 10th: Kay Square Press, a new publishing company focused on Philadelphia-area artists, their stories, and their art; and Kay Square's first release, 'With the Rich and Mighty: Emlen Etting of Philadelphia' (ISBN: 978-0-9815129-0-7), a critical biography by Kenneth C. Kaleta.

FlatSigned Press Alleges Don Imus Remarks Damage Legacy of President Gerald R. Ford
NEW YORK, N.Y. -- Nathan Yungerberg, an accomplished model scout and professional child photographer is launching a nation-wide casting call to find the cover model for his highly anticipated book release, 'The Model Child: A Parents Guide to the Child Modeling Industry' (ISBN: 978-0-9817018-0-6).

Books: On the Origin of Species

C >> Charles Darwin >> On the Origin of Species




It is certain, on the one hand, that the sterility of various species
when crossed is so different in degree and graduates away so
insensibly, and, on the other hand, that the fertility of pure species
is so easily affected by various circumstances, that for all practical
purposes it is most difficult to say where perfect fertility ends and
sterility begins. I think no better evidence of this can be required
than that the two most experienced observers who have ever lived,
namely, Kolreuter and Gartner, should have arrived at diametrically
opposite conclusions in regard to the very same species. It is also
most instructive to compare--but I have not space here to enter on
details--the evidence advanced by our best botanists on the question
whether certain doubtful forms should be ranked as species or
varieties, with the evidence from fertility adduced by different
hybridisers, or by the same author, from experiments made during
different years. It can thus be shown that neither sterility nor
fertility affords any clear distinction between species and varieties;
but that the evidence from this source graduates away, and is doubtful
in the same degree as is the evidence derived from other
constitutional and structural differences.

In regard to the sterility of hybrids in successive generations;
though Gartner was enabled to rear some hybrids, carefully guarding
them from a cross with either pure parent, for six or seven, and in
one case for ten generations, yet he asserts positively that their
fertility never increased, but generally greatly decreased. I do not
doubt that this is usually the case, and that the fertility often
suddenly decreases in the first few generations. Nevertheless I
believe that in all these experiments the fertility has been
diminished by an independent cause, namely, from close interbreeding.
I have collected so large a body of facts, showing that close
interbreeding lessens fertility, and, on the other hand, that an
occasional cross with a distinct individual or variety increases
fertility, that I cannot doubt the correctness of this almost
universal belief amongst breeders. Hybrids are seldom raised by
experimentalists in great numbers; and as the parent-species, or other
allied hybrids, generally grow in the same garden, the visits of
insects must be carefully prevented during the flowering season: hence
hybrids will generally be fertilised during each generation by their
own individual pollen; and I am convinced that this would be injurious
to their fertility, already lessened by their hybrid origin. I am
strengthened in this conviction by a remarkable statement repeatedly
made by Gartner, namely, that if even the less fertile hybrids be
artificially fertilised with hybrid pollen of the same kind, their
fertility, notwithstanding the frequent ill effects of manipulation,
sometimes decidedly increases, and goes on increasing. Now, in
artificial fertilisation pollen is as often taken by chance (as I know
from my own experience) from the anthers of another flower, as from
the anthers of the flower itself which is to be fertilised; so that a
cross between two flowers, though probably on the same plant, would be
thus effected. Moreover, whenever complicated experiments are in
progress, so careful an observer as Gartner would have castrated his
hybrids, and this would have insured in each generation a cross with
the pollen from a distinct flower, either from the same plant or from
another plant of the same hybrid nature. And thus, the strange fact of
the increase of fertility in the successive generations of
ARTIFICIALLY FERTILISED hybrids may, I believe, be accounted for by
close interbreeding having been avoided.

Now let us turn to the results arrived at by the third most
experienced hybridiser, namely, the Honourable and Reverend W.
Herbert. He is as emphatic in his conclusion that some hybrids are
perfectly fertile--as fertile as the pure parent-species--as are
Kolreuter and Gartner that some degree of sterility between distinct
species is a universal law of nature. He experimentised on some of the
very same species as did Gartner. The difference in their results may,
I think, be in part accounted for by Herbert's great horticultural
skill, and by his having hothouses at his command. Of his many
important statements I will here give only a single one as an example,
namely, that "every ovule in a pod of Crinum capense fertilised by C.
revolutum produced a plant, which (he says) I never saw to occur in a
case of its natural fecundation." So that we here have perfect, or
even more than commonly perfect, fertility in a first cross between
two distinct species.

This case of the Crinum leads me to refer to a most singular fact,
namely, that there are individual plants, as with certain species of
Lobelia, and with all the species of the genus Hippeastrum, which can
be far more easily fertilised by the pollen of another and distinct
species, than by their own pollen. For these plants have been found to
yield seed to the pollen of a distinct species, though quite sterile
with their own pollen, notwithstanding that their own pollen was found
to be perfectly good, for it fertilised distinct species. So that
certain individual plants and all the individuals of certain species
can actually be hybridised much more readily than they can be
self-fertilised! For instance, a bulb of Hippeastrum aulicum produced
four flowers; three were fertilised by Herbert with their own pollen,
and the fourth was subsequently fertilised by the pollen of a compound
hybrid descended from three other and distinct species: the result was
that "the ovaries of the three first flowers soon ceased to grow, and
after a few days perished entirely, whereas the pod impregnated by the
pollen of the hybrid made vigorous growth and rapid progress to
maturity, and bore good seed, which vegetated freely." In a letter to
me, in 1839, Mr. Herbert told me that he had then tried the experiment
during five years, and he continued to try it during several
subsequent years, and always with the same result. This result has,
also, been confirmed by other observers in the case of Hippeastrum
with its sub-genera, and in the case of some other genera, as Lobelia,
Passiflora and Verbascum. Although the plants in these experiments
appeared perfectly healthy, and although both the ovules and pollen of
the same flower were perfectly good with respect to other species, yet
as they were functionally imperfect in their mutual self-action, we
must infer that the plants were in an unnatural state. Nevertheless
these facts show on what slight and mysterious causes the lesser or
greater fertility of species when crossed, in comparison with the same
species when self-fertilised, sometimes depends.

The practical experiments of horticulturists, though not made with
scientific precision, deserve some notice. It is notorious in how
complicated a manner the species of Pelargonium, Fuchsia, Calceolaria,
Petunia, Rhododendron, etc., have been crossed, yet many of these
hybrids seed freely. For instance, Herbert asserts that a hybrid from
Calceolaria integrifolia and plantaginea, species most widely
dissimilar in general habit, "reproduced itself as perfectly as if it
had been a natural species from the mountains of Chile." I have taken
some pains to ascertain the degree of fertility of some of the complex
crosses of Rhododendrons, and I am assured that many of them are
perfectly fertile. Mr. C. Noble, for instance, informs me that he
raises stocks for grafting from a hybrid between Rhododendron Ponticum
and Catawbiense, and that this hybrid "seeds as freely as it is
possible to imagine." Had hybrids, when fairly treated, gone on
decreasing in fertility in each successive generation, as Gartner
believes to be the case, the fact would have been notorious to
nurserymen. Horticulturists raise large beds of the same hybrids, and
such alone are fairly treated, for by insect agency the several
individuals of the same hybrid variety are allowed to freely cross
with each other, and the injurious influence of close interbreeding is
thus prevented. Any one may readily convince himself of the efficiency
of insect-agency by examining the flowers of the more sterile kinds of
hybrid rhododendrons, which produce no pollen, for he will find on
their stigmas plenty of pollen brought from other flowers.

In regard to animals, much fewer experiments have been carefully tried
than with plants. If our systematic arrangements can be trusted, that
is if the genera of animals are as distinct from each other, as are
the genera of plants, then we may infer that animals more widely
separated in the scale of nature can be more easily crossed than in
the case of plants; but the hybrids themselves are, I think, more
sterile. I doubt whether any case of a perfectly fertile hybrid animal
can be considered as thoroughly well authenticated. It should,
however, be borne in mind that, owing to few animals breeding freely
under confinement, few experiments have been fairly tried: for
instance, the canary-bird has been crossed with nine other finches,
but as not one of these nine species breeds freely in confinement, we
have no right to expect that the first crosses between them and the
canary, or that their hybrids, should be perfectly fertile. Again,
with respect to the fertility in successive generations of the more
fertile hybrid animals, I hardly know of an instance in which two
families of the same hybrid have been raised at the same time from
different parents, so as to avoid the ill effects of close
interbreeding. On the contrary, brothers and sisters have usually been
crossed in each successive generation, in opposition to the constantly
repeated admonition of every breeder. And in this case, it is not at
all surprising that the inherent sterility in the hybrids should have
gone on increasing. If we were to act thus, and pair brothers and
sisters in the case of any pure animal, which from any cause had the
least tendency to sterility, the breed would assuredly be lost in a
very few generations.

Although I do not know of any thoroughly well-authenticated cases of
perfectly fertile hybrid animals, I have some reason to believe that
the hybrids from Cervulus vaginalis and Reevesii, and from Phasianus
colchicus with P. torquatus and with P. versicolor are perfectly
fertile. The hybrids from the common and Chinese geese (A. cygnoides),
species which are so different that they are generally ranked in
distinct genera, have often bred in this country with either pure
parent, and in one single instance they have bred inter se. This was
effected by Mr. Eyton, who raised two hybrids from the same parents
but from different hatches; and from these two birds he raised no less
than eight hybrids (grandchildren of the pure geese) from one nest. In
India, however, these cross-bred geese must be far more fertile; for I
am assured by two eminently capable judges, namely Mr. Blyth and Capt.
Hutton, that whole flocks of these crossed geese are kept in various
parts of the country; and as they are kept for profit, where neither
pure parent-species exists, they must certainly be highly fertile.

A doctrine which originated with Pallas, has been largely accepted by
modern naturalists; namely, that most of our domestic animals have
descended from two or more aboriginal species, since commingled by
intercrossing. On this view, the aboriginal species must either at
first have produced quite fertile hybrids, or the hybrids must have
become in subsequent generations quite fertile under domestication.
This latter alternative seems to me the most probable, and I am
inclined to believe in its truth, although it rests on no direct
evidence. I believe, for instance, that our dogs have descended from
several wild stocks; yet, with perhaps the exception of certain
indigenous domestic dogs of South America, all are quite fertile
together; and analogy makes me greatly doubt, whether the several
aboriginal species would at first have freely bred together and have
produced quite fertile hybrids. So again there is reason to believe
that our European and the humped Indian cattle are quite fertile
together; but from facts communicated to me by Mr. Blyth, I think they
must be considered as distinct species. On this view of the origin of
many of our domestic animals, we must either give up the belief of the
almost universal sterility of distinct species of animals when
crossed; or we must look at sterility, not as an indelible
characteristic, but as one capable of being removed by domestication.

Finally, looking to all the ascertained facts on the intercrossing of
plants and animals, it may be concluded that some degree of sterility,
both in first crosses and in hybrids, is an extremely general result;
but that it cannot, under our present state of knowledge, be
considered as absolutely universal.

LAWS GOVERNING THE STERILITY OF FIRST CROSSES AND OF HYBRIDS.

We will now consider a little more in detail the circumstances and
rules governing the sterility of first crosses and of hybrids. Our
chief object will be to see whether or not the rules indicate that
species have specially been endowed with this quality, in order to
prevent their crossing and blending together in utter confusion. The
following rules and conclusions are chiefly drawn up from Gartner's
admirable work on the hybridisation of plants. I have taken much pains
to ascertain how far the rules apply to animals, and considering how
scanty our knowledge is in regard to hybrid animals, I have been
surprised to find how generally the same rules apply to both kingdoms.

It has been already remarked, that the degree of fertility, both of
first crosses and of hybrids, graduates from zero to perfect
fertility. It is surprising in how many curious ways this gradation
can be shown to exist; but only the barest outline of the facts can
here be given. When pollen from a plant of one family is placed on the
stigma of a plant of a distinct family, it exerts no more influence
than so much inorganic dust. From this absolute zero of fertility, the
pollen of different species of the same genus applied to the stigma of
some one species, yields a perfect gradation in the number of seeds
produced, up to nearly complete or even quite complete fertility; and,
as we have seen, in certain abnormal cases, even to an excess of
fertility, beyond that which the plant's own pollen will produce. So
in hybrids themselves, there are some which never have produced, and
probably never would produce, even with the pollen of either pure
parent, a single fertile seed: but in some of these cases a first
trace of fertility may be detected, by the pollen of one of the pure
parent-species causing the flower of the hybrid to wither earlier than
it otherwise would have done; and the early withering of the flower is
well known to be a sign of incipient fertilisation. From this extreme
degree of sterility we have self-fertilised hybrids producing a
greater and greater number of seeds up to perfect fertility.

Hybrids from two species which are very difficult to cross, and which
rarely produce any offspring, are generally very sterile; but the
parallelism between the difficulty of making a first cross, and the
sterility of the hybrids thus produced--two classes of facts which are
generally confounded together--is by no means strict. There are many
cases, in which two pure species can be united with unusual facility,
and produce numerous hybrid-offspring, yet these hybrids are
remarkably sterile. On the other hand, there are species which can be
crossed very rarely, or with extreme difficulty, but the hybrids, when
at last produced, are very fertile. Even within the limits of the same
genus, for instance in Dianthus, these two opposite cases occur.

The fertility, both of first crosses and of hybrids, is more easily
affected by unfavourable conditions, than is the fertility of pure
species. But the degree of fertility is likewise innately variable;
for it is not always the same when the same two species are crossed
under the same circumstances, but depends in part upon the
constitution of the individuals which happen to have been chosen for
the experiment. So it is with hybrids, for their degree of fertility
is often found to differ greatly in the several individuals raised
from seed out of the same capsule and exposed to exactly the same
conditions.

By the term systematic affinity is meant, the resemblance between
species in structure and in constitution, more especially in the
structure of parts which are of high physiological importance and
which differ little in the allied species. Now the fertility of first
crosses between species, and of the hybrids produced from them, is
largely governed by their systematic affinity. This is clearly shown
by hybrids never having been raised between species ranked by
systematists in distinct families; and on the other hand, by very
closely allied species generally uniting with facility. But the
correspondence between systematic affinity and the facility of
crossing is by no means strict. A multitude of cases could be given of
very closely allied species which will not unite, or only with extreme
difficulty; and on the other hand of very distinct species which unite
with the utmost facility. In the same family there may be a genus, as
Dianthus, in which very many species can most readily be crossed; and
another genus, as Silene, in which the most persevering efforts have
failed to produce between extremely close species a single hybrid.
Even within the limits of the same genus, we meet with this same
difference; for instance, the many species of Nicotiana have been more
largely crossed than the species of almost any other genus; but
Gartner found that N. acuminata, which is not a particularly distinct
species, obstinately failed to fertilise, or to be fertilised by, no
less than eight other species of Nicotiana. Very many analogous facts
could be given.

No one has been able to point out what kind, or what amount, of
difference in any recognisable character is sufficient to prevent two
species crossing. It can be shown that plants most widely different in
habit and general appearance, and having strongly marked differences
in every part of the flower, even in the pollen, in the fruit, and in
the cotyledons, can be crossed. Annual and perennial plants, deciduous
and evergreen trees, plants inhabiting different stations and fitted
for extremely different climates, can often be crossed with ease.

By a reciprocal cross between two species, I mean the case, for
instance, of a stallion-horse being first crossed with a female-ass,
and then a male-ass with a mare: these two species may then be said to
have been reciprocally crossed. There is often the widest possible
difference in the facility of making reciprocal crosses. Such cases
are highly important, for they prove that the capacity in any two
species to cross is often completely independent of their systematic
affinity, or of any recognisable difference in their whole
organisation. On the other hand, these cases clearly show that the
capacity for crossing is connected with constitutional differences
imperceptible by us, and confined to the reproductive system. This
difference in the result of reciprocal crosses between the same two
species was long ago observed by Kolreuter. To give an instance:
Mirabilis jalappa can easily be fertilised by the pollen of M.
longiflora, and the hybrids thus produced are sufficiently fertile;
but Kolreuter tried more than two hundred times, during eight
following years, to fertilise reciprocally M. longiflora with the
pollen of M. jalappa, and utterly failed. Several other equally
striking cases could be given. Thuret has observed the same fact with
certain sea-weeds or Fuci. Gartner, moreover, found that this
difference of facility in making reciprocal crosses is extremely
common in a lesser degree. He has observed it even between forms so
closely related (as Matthiola annua and glabra) that many botanists
rank them only as varieties. It is also a remarkable fact, that
hybrids raised from reciprocal crosses, though of course compounded of
the very same two species, the one species having first been used as
the father and then as the mother, generally differ in fertility in a
small, and occasionally in a high degree.

Several other singular rules could be given from Gartner: for
instance, some species have a remarkable power of crossing with other
species; other species of the same genus have a remarkable power of
impressing their likeness on their hybrid offspring; but these two
powers do not at all necessarily go together. There are certain
hybrids which instead of having, as is usual, an intermediate
character between their two parents, always closely resemble one of
them; and such hybrids, though externally so like one of their pure
parent-species, are with rare exceptions extremely sterile. So again
amongst hybrids which are usually intermediate in structure between
their parents, exceptional and abnormal individuals sometimes are
born, which closely resemble one of their pure parents; and these
hybrids are almost always utterly sterile, even when the other hybrids
raised from seed from the same capsule have a considerable degree of
fertility. These facts show how completely fertility in the hybrid is
independent of its external resemblance to either pure parent.

Considering the several rules now given, which govern the fertility of
first crosses and of hybrids, we see that when forms, which must be
considered as good and distinct species, are united, their fertility
graduates from zero to perfect fertility, or even to fertility under
certain conditions in excess. That their fertility, besides being
eminently susceptible to favourable and unfavourable conditions, is
innately variable. That it is by no means always the same in degree in
the first cross and in the hybrids produced from this cross. That the
fertility of hybrids is not related to the degree in which they
resemble in external appearance either parent. And lastly, that the
facility of making a first cross between any two species is not always
governed by their systematic affinity or degree of resemblance to each
other. This latter statement is clearly proved by reciprocal crosses
between the same two species, for according as the one species or the
other is used as the father or the mother, there is generally some
difference, and occasionally the widest possible difference, in the
facility of effecting an union. The hybrids, moreover, produced from
reciprocal crosses often differ in fertility.

Now do these complex and singular rules indicate that species have
been endowed with sterility simply to prevent their becoming
confounded in nature? I think not. For why should the sterility be so
extremely different in degree, when various species are crossed, all
of which we must suppose it would be equally important to keep from
blending together? Why should the degree of sterility be innately
variable in the individuals of the same species? Why should some
species cross with facility, and yet produce very sterile hybrids; and
other species cross with extreme difficulty, and yet produce fairly
fertile hybrids? Why should there often be so great a difference in
the result of a reciprocal cross between the same two species? Why, it
may even be asked, has the production of hybrids been permitted? to
grant to species the special power of producing hybrids, and then to
stop their further propagation by different degrees of sterility, not
strictly related to the facility of the first union between their
parents, seems to be a strange arrangement.

The foregoing rules and facts, on the other hand, appear to me clearly
to indicate that the sterility both of first crosses and of hybrids is
simply incidental or dependent on unknown differences, chiefly in the
reproductive systems, of the species which are crossed. The
differences being of so peculiar and limited a nature, that, in
reciprocal crosses between two species the male sexual element of the
one will often freely act on the female sexual element of the other,
but not in a reversed direction. It will be advisable to explain a
little more fully by an example what I mean by sterility being
incidental on other differences, and not a specially endowed quality.
As the capacity of one plant to be grafted or budded on another is so
entirely unimportant for its welfare in a state of nature, I presume
that no one will suppose that this capacity is a SPECIALLY endowed
quality, but will admit that it is incidental on differences in the
laws of growth of the two plants. We can sometimes see the reason why
one tree will not take on another, from differences in their rate of
growth, in the hardness of their wood, in the period of the flow or
nature of their sap, etc.; but in a multitude of cases we can assign
no reason whatever. Great diversity in the size of two plants, one
being woody and the other herbaceous, one being evergreen and the
other deciduous, and adaptation to widely different climates, does not
always prevent the two grafting together. As in hybridisation, so with
grafting, the capacity is limited by systematic affinity, for no one
has been able to graft trees together belonging to quite distinct
families; and, on the other hand, closely allied species, and
varieties of the same species, can usually, but not invariably, be
grafted with ease. But this capacity, as in hybridisation, is by no
means absolutely governed by systematic affinity. Although many
distinct genera within the same family have been grafted together, in
other cases species of the same genus will not take on each other. The
pear can be grafted far more readily on the quince, which is ranked as
a distinct genus, than on the apple, which is a member of the same
genus. Even different varieties of the pear take with different
degrees of facility on the quince; so do different varieties of the
apricot and peach on certain varieties of the plum.