Test: LSAT Reading

Adapted from Darwinism by Alfred Russel Wallace (1889)

Everyone knows that in each litter of kittens or of puppies no two are alike. Even in the case in which several are exactly alike in colors, other differences are always perceptible to those who observe them closely. They will differ in size, in the proportions of their bodies and limbs, and in the length or texture of their hairy covering. They each possess, too, an individual countenance; we all know that each kitten in the successive families of our old favorite cat has a face of its own, distinct from all its brothers and sisters. Now this individual variability exists among all creatures that we can closely observe, even when the two parents are very much alike and have been matched in order to preserve some special breed. The same thing occurs in the vegetable kingdom. All plants raised from seed differ more or less from each other. In every bed of flowers or of vegetables we shall find, if we look closely, that there are countless small differences, in the size, in the mode of growth, in the shape or color of the leaves, in the form, color, or markings of the flowers, or in the size, form, color, or flavor of the fruit. These differences are usually small, but are yet easily seen, and in their extremes are very considerable; and some of these differences have this important quality, that they have a tendency to be reproduced, and thus by careful breeding certain particular variations or groups of variations can be increased to an enormous extent—apparently to any extent not incompatible with the life, growth, and reproduction of the plant or animal.

The way this is done is by artificial selection, and it is very important to understand this process and its results. Suppose we have a plant with a small edible seed, and we want to increase the size of that seed. Suppose also that the maximum size of a seed of this type of plant is solely dependent on the maximum sizes of the seeds of its parents. We grow as large a quantity of it as possible, and when the crop is ripe we carefully choose a few of the very largest seeds, or we may by means of a sieve sort out a quantity of the largest seeds. Next year we sow only these large seeds, taking care to give them suitable soil and manure, and the result is found to be that the average size of the seeds is larger than in the first crop, and that the largest seeds are now somewhat larger and more numerous. Again sowing these, we obtain a further slight increase of size, and in a very few years we obtain a greatly improved type that will always produce larger seeds than the unaltered type, even if cultivated without any special care. In this way all our fine sorts of cultivated vegetables, fruits, and flowers have been obtained, all our choice breeds of cattle or of poultry, our wonderful racehorses, and our endless varieties of dogs. It is a very common but mistaken idea that this improvement is due to crossing and feeding in the case of animals, and to improved cultivation in the case of plants. Crossing is occasionally used in order to obtain a combination of qualities found in two distinct breeds, and also because it is found to increase the constitutional vigor; but every breed is the result of the selection of variations occurring year after year and accumulated in the manner just described. Repeated selection in favor of certain traits is the foundation of all of the controlled changes made in our breeds of domestic animals and strains of cultivated plants.

1.

The author's tone indicates that most people view artificial selection __________.

as a dangerous idea that should not be discussed

as something not worth understanding

as a legitimate threat to their belief systems

as a widely known fact

as a confusing topic

1/2 questions

0%

Access results and powerful study features!

Take 15 seconds to create an account.
Start now! Create your free account and get access to features like:
  • Full length diagnostic tests
  • Invite your friends
  • Access hundreds of practice tests
  • Monitor your progress over time
  • Manage your tests and results
  • Monitor the progress of your class & students
By clicking Create Account you agree that you are at least 13 years old and you agree to the Varsity Tutors LLC Terms of Use and Privacy Policy.
Learning Tools by Varsity Tutors