How have all those exquisite adaptations
of one part of the organisation to another part, and to the conditions
of life, and of one distinct organic being to another being, been perfected?
We see these beautiful co-adaptations most plainly in the woodpecker
and missletoe; and only a little less plainly in the humblest parasite
which clings to the hairs of a quadruped or feather of a bird; .
. . in short, we see beautiful adaptation everywhere and in every
part of the organic world.
Summary
Darwin begins the bulk of his argument here, explaining
how different species are created. Two concepts dominate this explanation: the
struggle for existence and natural selection. Darwin suggests that
an organism’s struggle for existence is part of what determines why
some species’ characteristics survive and others become extinct.
The great number of variations in species have allowed plants and
animals to become beautifully adapted to their environments. Darwin
provides examples of these adaptations. He mentions the beak of
a woodpecker, which allows it to gather insects for food; the structure
of a parasite, which allows it to attach to and feed off of another
organism; and the ability of a beetle to dive into the water to
gather food. These adaptations illustrate how unique characteristics
of particular organisms have developed, allowing them to thrive
in their specific environments. 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.
Two other concepts, the struggle for life and the limits
of population increase, frame the idea of an organism’s drive to
exist. Although nature can provide an abundance of food and shelter
to its inhabitants, it can also be destructive, causing a struggle
for life. Natural disasters, epidemics, and shifts in climate can
limit the availability of food and shelter, and animals prey on
other plants and animals. Nature inherently disallows the survival
of some organisms. Darwin’s principle of the limits of population
increase, borrowed from economist Thomas Malthus, is based on the
notion that each successive generation of species exponentially
increases its population, growing the world population on a constant
basis. If each generation continues to reproduce in greater numbers
than the one before, and the rate of death remains the same, the
earth will eventually run out of room and will be unable to support
all of its inhabitants. Therefore, nature limits the number of possible
inhabitants of the world. As a result, each individual organism
must compete to continue existing, and because there must be a limit
on population for every species, one individual organism’s survival inherently
threatens the survival of another.
The constant competition for existence compels all organisms and
species to strive to outlive others and successfully leave offspring
for the survival of the species. Most important to Darwin’s theory
is the survival of progeny, because future generations are both
dependent on and essential to the perpetuation of advantageous traits
and the progress of their race. While much of the competition for
existence takes place between members of different species, the
most important struggle is between members of the same species.
Those individual members who hold advantageous variations that allow
them to avoid predators, withstand climate changes, and survive
natural disasters have the best chance of surviving. An advantageous
variation, combined with successful reproduction, can result in
a change in the species, creating a subspecies better equipped to
handle its environment. Survival does not occur by chance. Rather,
it is the result of advantageous variations.
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. In some cases, however, relationships between
species govern the chances of survival. Darwin points out that a
single tree planted in any area allows further vegetation to grow
there and that the fencing off of a section of land to keep cattle away
allows seedlings to flourish. In these cases, the survival of a tree
or removal of cattle allows the growth of an entirely different species.
Struggles for survival are dependent on others, whether those struggles
end up being competitive or cooperative in nature.
Analysis
In this chapter, although Darwin begins to get to the
heart of his theory of evolution, he continues to highlight how
the work of others helped him form his theory. In particular, he
credits economist Thomas Malthus for contributing the theory of
a struggle for existence, one of the key concepts driving his own
theory. Malthus’s theory provides a rationale for why many species
become extinct: In the competition to continue living, the traits
that allow species to survive shape the descent of new species,
providing the impetus for natural selection. Darwin also uses Malthus’s
theory to delve into an entirely different realm of scientific thought,
using mathematics and statistics to define the model of population
growth. Darwin demonstrates the value of drawing on several scientific
fields (in this case, botany, zoology, and mathematics) to construct
a scientific theory.
Darwin’s notion of the struggle for existence personifies
nature’s contradictions. He reflects on the beautiful and benevolent
qualities of nature, which creates many different beings with adaptations that
are perfectly constructed for individual organisms’ survival. Darwin
also paints a darker picture: Nature can provide abundance for survival,
but it can also be destructive. Geography limits population growth,
and nature’s changes can destroy life. The search for food also
creates inherent destruction, as animals must prey on plants and
one another for sustenance. These portrayals of nature as both a
benevolent and cruel force can lead to the misinterpretation of
natural selection as a clash between forces of good and evil.
