MAIN PARTS TO THEORY
• Every species is fertile enough that if all offspring survived to reproduce the population would grow (fact).
• Despite periodic fluctuations, populations remain roughly the same size (fact).
• Resources such as food are limited and are relatively stable over time (fact).
• A struggle for survival ensues (inference).
• Individuals in a population vary significantly from one another (fact).
• Much of this variation is inheritable (fact).
• Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to
the environment are more likely to survive and more likely to reproduce and leave their inheritable traits to future generations, which
produces the process of natural selection (inference).
• This slowly effected process results in populations changing to adapt to their environments, and ultimately, these
variations accumulate over time to form new species (inference).
Chapter I is that heredity is the key to explaining variation.
selection to analyze the development of race types within species. In discussing selection,
he notes that some traits are more useful or helpful than others and that these traits will be
selected both consciously (by breeders) and unconsciously as the species evolves.
Unconsciously selected traits develop naturally over time, often helping certain species
adapt to their environments and increase their rates of survival.
Darwin’s conclusions about variations also contradict the idea, widely held at the time, that an act of
God created species independently. Darwin’s use of the termcreation is ambiguous here, but it could
easily be interpreted as a reference to creationism (the idea that God created each species). Darwin’s
reference to creationism is an implied critique of the teachings of Christianity—a daring move, given
the influence of Christianity in Darwin’s time. Darwin suggests that the range of variations within
species and between the larger genera and smaller species proves that the theory of divine creation is
flawed. If each species formed independently of one another, Darwin argues, there would be no
reason or explanation for the existence of so many variations.
Darwin’s criticism bolsters his theory that different species must have descended from one parent
Two concepts dominate this explanation: the struggle for existence and natural selection.
The most advantageous characteristics are preserved and passed on to offspring. Darwin explains that
the presence of these useful adaptations in organisms is the result of natural selection.
Finally, Darwin indicates different ways in which the struggle for existence can occur in the natural
world. Most cases of survival involve one organism or group possessing an advantage over another one and beating it out. Generally, a species with a larger population has a greater chance of survival
than a species with a smaller population, as its larger population makes it less likely to be wiped out by
prey and better able to maintain its great numbers through reproduction
The concept of the struggle for existence may be applied, by extension, to human society. If
geometrical population increase is limited in the natural world due to geography and natural resources,
human population increase must also have its limits. Do humans engage in a competition for
continued existence? If so, do they have to fight one another to survive? Or, might humans work
together to survive, as in Darwin’s example of the tree and plants? Also, are humans with the most
advantageous positions (in the workforce, for example) winning the battle? In a broader sense, the
implied question of whether humans fight to live again casts doubt on the strictness of the separation
between humans and the natural world. What Darwin’s work says about human life spawned much of
the controversy surrounding The Origin of Species—and modern evolutionary theory.
Astruggle for existence inevitably follows from the high rate at which all organic beings
tend to increase. Every being, which during its natural lifetime produces several eggs or