1. Excerpts from Darwin's
"On the Origin of Species"*
Leandro Nunes de Castro
Lnunes@mackenzie.br
@lndecastro
Faculdade de Computação e Informática &
Programa de Pós-Graduação em Engenharia Elétrica
Laboratório de Computação Natural (LCoN)
www.mackenzie.br/lcon.html
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* Darwin, C. R. (1859), The Origin of Species, Wordsworth Editions Limited (1998).

2. Summary
PART 1
Introduction
1. Variation Under Domestication
2. Variation Under Nature
3. Struggle for Existence
4. Natural Selection
5. Laws of Variation
6. Difficulties on Theory
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3. Introduction
3

4. • Born in England in 1809
• Started medicine at the
Edinburgh University in 1827 and
Theology at Cambridge in 1829
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5. From 1831 to 1836 Darwin joined the HMS
Beagle expedition to the Southern Hemisphere,
Brazil and Galapagos Archipelago
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6. • By the 1850’s, Darwin’s research had turned into a massive
ongoing book, Natural Selection.
• Alfred Russell Wallace, a young socialist naturalist collecting and
researching in the Malay Archipelago, had been communicating
with Darwin, and sending him specimens.
• He had also sketched out his own theories of the evolutionary
mechanism, which Darwin, recognizing their similarity to his own,
had complacently encouraged Wallace to develop.
• On 18 June 1858, a twenty-page letter arrived from Wallace,
containing – in effect – an outline of the natural selection theory.
• Incapable of acting dishonorably, Darwin proposed to help gain
due public recognition for Wallace’s work, while having to
confront the painful truth that his own dilatory perfectionism had
led to him being upstaged.
• A delicate compromise was thus reached: Wallace’s letter and
relevant extracts from Darwin’s work were presented together at
a meeting of the Linnean Society of London on 1 July 1958.
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Darwin x Wallace

7. 1. Variation Under
Domestication
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8. “*w+hen we look to the individuals of the same
variety or sub-variety of our older cultivated
plants and animals, one of the first points which
strikes us, is that they generally differ much
more from each other than do the individuals of
any one species or variety in a state of nature”.
(p. 8)
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Discussions about domestic breeding

9. “But I am strongly inclined
to suspect that the most
frequent cause of
variability may be
attributed to the male and
female reproductive
elements having been
affected prior to the act of
conception.” (p. 9)
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Genetics was still unknown

10. “Seedlings from the same fruit, and the young of
the same litter, sometimes differ considerably from
each other, though both the young and the parents,
as Müller has remarked, have apparently been
exposed to exactly the same conditions of life; and
this shows how unimportant the direct effects of
the conditions of life are in comparison with the
laws of reproduction, and of growth, and of
inheritance; for had the action of the conditions
been direct, if any of the young had varied, all
would probably have varied in the same manner.”
(p. 10)
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Contrasting with Lamarck

11. “*a+ny variation which is not inherited is unimportant
for us.” (p. 12)
“Perhaps the correct way of viewing the whole
subject, would be, to look at the inheritance of every
character whatever as the rule, and non-inheritance
as the anomaly”(p. 13)
“…by crossing we can get only forms in some degree
intermediate between their parents…” (p. 17)
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Importance of inheritance

12. “…as a general rule, I cannot
doubt that the continued
selection of slight
variations…will produce races
differing from each other…” (p.
28)
“…I am convinced that the
accumulative action of
Selection, whether applied
methodically and more quickly,
or unconsciously and more
slowly, but more efficiently, is
by far the predominant Power.”
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Natural Selection

13. 2. Variation Under Nature
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14. 14
What is a species
“Nor shall I here discuss the
various definitions which
have been given of the term
species. No one definition
has yet satisfied all
naturalists; yet every
naturalist knows vaguely
what he means when he
speaks of a species.” (p. 36)

15. “Those forms which possess in some considerable degree the
character of species, but which are so closely similar to some other
forms, or are so closely linked to them by intermediate gradations,
that naturalists do not like to rank them as distinct
species…Practically, when a naturalist can unite two forms together
by others having intermediate characters, he treats the one as a
variety of the other, ranking the most common, but sometimes the
one first described, as the species, and the other as the variety.” (p.
38)
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Variety

16. “I was much struck how entirely vague and
arbitrary is the distinction between species and
variety.” (p. 39)
“…I look at the term species, as one arbitrary
given for the sake of convenience to a set of
individuals closely resembling each other, and
that it does not essentially differ from the term
variety, which is given to less distinct and more
fluctuating forms.” (p. 42)
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Species vs Variety

17. 3. Struggle for Existence
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18. “I have called this principle, by which each slight
variation, if useful, is preserved, by the term of
Natural Selection, in order to mark its relation to
man’s power of selection.” (p. 49)
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Natural Selection

19. “Every being, which during its natural lifetime
produces several eggs or seeds, must suffer
destruction during some period of its life, and
during some season or occasional year, otherwise,
on the principle of geometrical increase, its
numbers would quickly become so inordinately
great that no country could support the product.
Hence, as more individuals are produced than can
possibly survive, there must in every case be a
struggle for existence, either one individual with
another of the same species, or with the individuals
of distinct species, or with the physical conditions
of life.” (p. 50)
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Struggle for existence

20. “*t+here is no exception to the rule that every
organic being naturally increases at so a high
rate, that if not destroyed, the earth would
soon be covered by the progeny of a single
pair.” (p. 51)
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Struggle for existence

21. “The elephant is reckoned to be the slowest
breeder of all known animals, and I have taken
some pains to estimate its probable minimum
rate of natural increase: it will be under the
mark to assume that it breeds when thirty years
old, and goes on breeding till ninety years old,
bringing forth three pairs of young in this
interval; if this be so, at the end of the fifth
century there would be alive fifteen million
elephants, descended from the first pair.” (p. 51)
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Geometrical increase

22. 4. Natural Selection
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23. “…can we doubt…that individuals having any
advantage, however slight, over others, would have
the best chance of surviving and of procreating
their kind? On the other hand, we may feel sure
that any variation in the last degree injurious would
be rigidly destroyed. This preservation of favourable
variations and the rejection of injurious variations, I
call Natural Selection. Variations neither useful nor
injurious would not be affected by natural selection,
and would be left a fluctuating element, as perhaps
we see in the species called polymorphic.” (p. 65)
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Darwin’s belief in Natural Selection

24. “…I think it inevitably follows,
that as new species in the
course of time are formed
through natural selection,
others will become rarer and
rarer, and finally extinct. The
forms which stand in closest
competition with those
undergoing modification and
improvement, will naturally
suffer most.” (p. 85-86)
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Extinction

25. “I believe…that the more diversified the
descendants from any one species become in
structure, constitution, and habits, by so
much will they be better enabled to seize on
many and widely diversified places in the
polity of nature, and so be enabled to
increase in numbers.” (p. 87)
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The importance of diversity

26. 5. Laws of Variation
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27. • Darwin believed that differences in character
were a result of variation in the reproductive
organs. But he strongly believed that these
and other changes are not a result of the
direct effect of the environment.
“How much direct effect difference of climate,
food, etc., produces on any being is extremely
doubtful. My impression is, that the effect is
extremely small in the case of animals, but
perhaps rather more in that of plants.” (p. 103)
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Environmental influence

28. • Use and disuse law.
• Acclimatization.
• Correlation of growth.
“Our ignorance of the
laws of variation is
profound” (p. 129)
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Some Laws of Variation

29. Difficulties on Theory
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30. 1. Is it possible that an animal having very specific structure
and habits could have been formed by the modification of
some animal with wholly different habits?
2. How can organs of extreme perfection and complication
be generated by natural selection?
3. Why are there organs of little apparent importance?
4. Can instincts be acquired and modified through natural
selection?
5. How can we account for species, when crossed, being
sterile and producing sterile offspring, whereas, when
varieties are crossed, their fertility is unimpaired?
6. Why, if species have descended from other species by
insensibly fine gradations, do we not everywhere see
innumerable transitional forms?
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Questions pointed out by Darwin

31. “In North America the black bear was seen by
Hearne swimming for hours with widely open
mouth, thus catching, like a whale, insects in the
water. Even in so extreme a case as this, if the
supply of insects were constant, and if better
adapted competitors did not already exist in the
country, I can see no difficulty in a race of bears
being rendered, by natural selection, more and
more aquatic in their structure and habits, with
larger and larger mouths, till a creature was
produced as monstrous as a whale.” (p. 141-142)
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Darwin’s support of Natural Selection

32. PART 2
7. Instinct
8. Hybridism
9. On the Imperfection of the Geological Record
10. On the Geological Succession of Organic Beings
11. Geographical Distribution
12. Geographical Distribution – Continued
13. Mutual Affinities of Organic Beings:
Morphology: Embryology: Rudimentary Organs
14. Recapitulation and Conclusions
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Summary

33. Thanks!
Leandro Nunes de Castro
Lnunes@mackenzie.br
@lndecastro
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