Summary
Darwin notes that domestic species contain much more variety
in their different subsets and races than species found in nature.
Scientists have traditionally attributed variations in species to
environmental factors, such as the availability of food or the climate
and heat conditions in which species types are raised. However,
Darwin rejects the idea that environmental factors are the primary
triggers of variation, because new varieties of even the oldest
known species have come into being without a change in environmental
conditions. Darwin also rejects the theory that habits of
use (of bodily structures, for instance) are the main cause
of variation. While he notes that in some species types the use
of particular organs has yielded different body structures (such
as the strong legs of ducks that don't fly versus the strong wings
of those that do), far starker variations exist that defy environmental
explanation.
The most important explanation for variation is reproduction. Parents
pass specific variations on to their offspring, and those variations
are perpetuated in subsequent generations. This explains why rare
traits occasionally pop up in individual plants or animals and then
appear again in those organisms' direct offspring. Darwin admits
that scientists don't yet fully understand the laws of inheritance
as they apply to parents and their offspring. For example, scientific
theory has not explained why offspring inherit traits on some occasions
but not others, or why certain traits skip generations entirely,
appearing in parents but not offspring, and then reappearing in
the offspring's offspring.
Furthermore, it remains unclear in many cases whether
species types are descended from one parent species (the original
species that gave birth to the others) or from several different
parent species. In his study of various breeds of domestic pigeons,
Darwin found that all pigeons share similar coloring and body structure. Additionally,
after cross-breeding several types of pigeons, he discovered that
the resultant hybrids were “perfectly fertile,” which indicates
that they descended from one parent species, as the offspring of
two distinct breeds are sterile. These findings suggested that,
despite wide variation in the types of pigeons, all must have descended
from the rock pigeon. Darwin concludes that most species types may,
in fact, have descended from one parent, rather than multiple parent
species, as breeders had previously believed.
Darwin discusses the breeding of domestic species and
man's influence on the creation of new races and subspecies. While
nature produces variations, in controlled environments man has the
power to select which variations will survive and influence future
generations. In a process known as conscious selection,
a domestic breeder selects the best or most useful types within
a species and breeds them over other types. This breeding creates
a large stock of those particularly useful types that are then more
readily available to breed in subsequent generations.
Domesticated species are also subject to unconscious
selection, a process by which characteristics become predominant
without the aid or influence of breeders. Gradual changes, often
unnoticeable at first, can account for differences in breeds over
time, such as the increased speed and size of English racehorses
compared to their original Arab stock. Valuable traits may be arbitrary
(related to beauty) or unarbitrary (such as size, weight, speed,
or other traits that may prove advantageous to the species). These
unconsciously selected traits may benefit the species types in unknown
ways, perhaps by allowing them to withstand famine or accidents
in order to reproduce and perpetuate the traits in their offspring.
The gradual nature of this process may explain why the original
parent stock of a species is difficult to determine: Since changes
occur slowly over time, two stocks that were once related can look
quite different after many generations.
Analysis
Darwin's major claim in Chapter I is that heredity is
the key to explaining variation. This argument contrasts slightly
with the arguments made by other evolutionary theorists, such as
Jean-Baptiste Lamarck, who claimed that environmental factors are
the best explanation for the development of species. Darwin does
not dismiss these earlier theories. In fact, he acknowledges that
environmental factors do play a role in species type differentiation.
His own example—the strong wings of flying ducks versus the strong
legs of non-flying ducks—supports the idea that
environmental factors affect species type development. Nonetheless,
in arguing that heredity plays the larger role, Darwin implicitly
criticizes Lamarck's theory even as he recognizes its importance.
He asks, If traits are passed through heredity rather than developed
through environmental use, can developed traits such as strong wings
then be passed on through heredity? Or must wing strength already
be a hereditary trait in itself? If strong wings are hereditary,
how is it that those ducks that fly are lucky enough to have this
trait in their hereditary makeup? Darwin poses these questions to
acknowledge that some of the mechanics of heredity remain unknown.
The other key component of Darwin's argument in Chapter
I is his use of the term 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.
For example, a trait that would allow a species to survive famines
or accidents might have been unconsciously selected if all other
species died when a natural disaster occurred. Famines and accidents
are natural occurrences, so the process of unconscious selection
hints that natural selection accounts for species development in
the wild. Darwin's discussion of selection in Chapter I lays the
groundwork for the crux of his evolutionary theory: his argument
for natural selection.
Through his own observations and experiments, Darwin suggests
that scientific methodology must be used to begin to understand
the mysteries of nature—mysteries that heretofore had been unexplained
or attributed to the workings of God. Moreover, Darwin illustrates
the importance of inductive reasoning, or drawing conclusions from
examples and observations, to the scientific process. By using examples
taken from scientific observation, Darwin establishes principles
of species development that would be impossible to infer on the
basis of existing scientific thought alone. By drawing on specific
observations, experiments, and conclusions based on research and
evidence, Darwin is able to negate previously held ideas, such as
the possibility of multiple parent species and Lamarck's notion
of the supposed dominant role of the environment in the development
of variation. And finally, Darwin acknowledges that science still
does not fully understand such concepts as the workings of heredity
in reproduction. This kind of acknowledgment recognizes the limits
of scientific inquiry and experimentation. Darwin's scientific methodologies
and processes point not only to the theories drawn from experimental
and inductive reasoning but also to the uncertainties and disagreements
inherent in the study of science.
