Excerpts from “On the Tendency of Varieties to Depart Indefinitely from the Original Type,” by Alfred Russel Wallace [Read July 1st, 1858].
The life of wild animals is a struggle for existence. The full exertion of all their
faculties and all their energies is required to preserve their own existence and
provide for that of their infant offspring. The possibility of procuring food during
the least favourable seasons, and of escaping the attacks of their most dangerous
enemies, are the primary conditions which determine the existence both of
individuals and of entire species. These conditions will also determine the population of a species; and by a careful consideration of all the circumstances we may be enabled to comprehend, and in some degree to explain, what at first sight appears so inexplicable—the excessive abundance of some species, while others closely allied to them are very rare. ...
... It is also evident that most changes would affect, either favourably or adversely, the powers of prolonging existence. An antelope with shorter or weaker legs must necessarily suffer more from the attacks of the feline carnivora; the passenger pigeon with less powerful wings would sooner or later be affected in its powers of procuring a regular
supply of food; and in both cases the result must necessarily be a diminution of the population of the modified species. If, on the other hand, any species should produce a variety having slightly increased powers of preserving existence that variety must inevitably in time acquire a superiority in numbers. ...
Complete the chart below for the excerpt from Wallace’s paper. Provide examples of evolution by natural selection that Wallace used in his writing. Describe the species, the variations among individuals, the selective pressure, and how species change over time.
2 examples must be provided for each question and species.
Wallace —Natural Selection
Species:
What trait varies within the species?
What is the selective pressure? (In other words, what causes some individuals to produce more offspring than others?)
How would the population change over time?
