A．the selection by a farmer of the best milk-producing ……
TEXT E
For hundreds of years,
farmers have selected and bred plants and animals to favor, or bring out,
characteristics they desired. For example, cows that produced large amounts of
milk were selected for breeding, while poor milk producers were not allowed to
reproduce. In like manner, horses were bred for speed and strength. Those having
these desired characteristics were selected for breeding. Over time, these
preferred breeds became more common than earlier, less desired types. This
selective breeding is called artificial selection.
In this
passage, Camp and Arms explain how this same process occurs naturally. The
theory of evolution by natural selection was put forward in a joint presentation
of the views of Charles Darwin and Alfred Russell Wallace before the Linnaean
Society of London in 1858. Darwin and Wallace were not the first to suggest that
evolution occurred; but their names are linked with the idea of evolution
because they proposed the theory of natural se- lection as the mechanism by
which evolution occurs. We are always more likely to believe in a process when
people explain how it happens than if they merely assert that it does.
The theory of evolution by means of natural selection is based on three
observations. First, as we can see by comparing one cat or human being with
another, the members of a species differ from one another; that is, there is
variation among individuals of the same species. Second, some (though not all)
of the differences between individuals are inherited. (Other differences are not
inherited, but are caused by different environments. For in- stance, two plants
with identical genes may grow to different sizes if one of them is planted in
poor soil. ) Third, more organisms are born than live to grow up and reproduced
many organisms die as embryos or seeds, as saplings, nestlings, or
larvae.
Inherited characteristics that improve an organism’s
chances of living and reproducing will be more common in the next generation and
those that decrease its chances of reproducing will be less common. Various
genes or combinations of genes will be naturally selected for or against, from
one generation to the next, depending on how they affect reproductive potential.
For natural selection to cause a change in a population from one generation to
the next (that is, to cause evolution), it is not necessary that all genes
affect survival and reproduction; the same result occurs if just some genes make
an individual more likely to grow up and reproduce.
Which of the following is NOT an example of artificial selection
A．the selection by a farmer of the best milk-producing cows for breeding
B．a breeder’s allowing only the fastest horses to reproduce
C．the selection for reproduction of the best egg-laying chickens by the farmer
D．an increase in the number of giraffes with long necks because of a decline in the number of low-lying plants used for feeding
