Megan Thorne
BSCI370
2/12/2016
Darwin’s Ideas of Natural Selection Exemplified
References
Darwin, Charles. "The Origin of Species." Literature.org. 23 May 2005. 28 Sept. 2008
<http://www.literature.org/authors/darwin-charles/the-origin-of-species/index.html>.
Freeman, Scott, and Jon C. Herron. Evolutionary Analysis. Upper Saddle River: Prentice Hall,
2006.
In 1859, naturalist Charles Darwin published On the Origin of Species, which argued that
organisms change over time or evolve based on genetic variation and natural selection of traits
that allow for better survival and increased reproduction.
In chapter ten of On the origin of Species, Darwin discusses some evidence for his theory
of natural selection. One of the first things he mentions in the chapter is extinction. Darwin
explains that extinction occurs when a species does not go through modifications over time, and
the species that it competes with do go through modifications that adapt them better to the
environment. The modified species prevail in the competition for survival and the species that
do not change eventually die out and become extinct. In the textbook Evolutionary Analysis,
an example given of an extinct species is the Irish elk. Baron Georges Cuvier discovered
fossils of the Irish elk in 1812. He did anatomical analyses on these fossils and determined that,
despite what others believed, it was neither a member of the moose family nor the reindeer
family, but it was a species of its own that went extinct (Textbook, 44). Both Darwin and the
authors of Evolutionary Analysis explain how the fact of extinction shows that species develop
and change over time; some die off completely, others are created, and the cycle continues
through the mechanism of natural selection.
Megan Thorne
BSCI370
2/12/2016
Darwin also wrote about “the law of succession,” which he explained to be the fact that
living species generally resembled fossil forms of species from their same location. Darwin said,
“If the inhabitants of one continent formerly differed greatly from those of another continent, so
will their modified descendants still differ in nearly the same manner and degree.” Darwin’s
notion behind this was that if species were immutable as the Theory of Special Creation
suggests, then they would not be chiefly produced in certain areas. Evolutionary Analysis gives
two examples of species that displayed the law of succession. Paleontologist William Clift
studied extinct mammals of Australia and found that they were marsupials and similar to
species living there now. Darwin studied armadillos from Argentina and found that they
were similar to the fossil forms found there. The text explains that the Australian species and
Argentinean species were not similar to each other, but they were similar to the fossils found on
their respective continents, showing that descent with modification occurred and, naturally, the
species stayed on the same continent.
Darwin touches on the concept of transitional species in chapter 10 as well. He says, “in a
perfectly natural classification many fossil species would have to stand between living
species…” The textbook lists a few examples of transitional species, the most popular one
probably being the fossil of the Archaeopteryx. The Archaeopteryx was a species that had a
bone structure very similar to that of a dinosaur, but it also had feathers and the ability to
fly, identifying it as a bird. The textbook states, “we call Archaeopteryx a transitional fossil
because it demonstrates the past existence of species intermediate in form between dinosaur and
bird” (Textbook, 47).
Earlier in this chapter, Darwin discusses how species branch off from one another to
diverge and create new types of species, and that it all starts with a common ancestor. He says
Megan Thorne
BSCI370
2/12/2016
the whole process is slow and gradual and it involves “one species giving rise first to two or
three varieties, these being slowly converted into species, which in their turn produce by equally
slow steps other species, and so on, like the branching of a great tree from a single stem, till the
group becomes large.” In the chapter in Evolutionary Analysis, the authors explain the visual
diagram version of this concept to be a phylogenetic or evolutionary tree. The book shows a
specific example of the evolutionary tree for eight species of cats. The tree shows how the
traits for the cats’ markings developed over time from the single, common ancestor with a
flecked coat pattern. It follows Darwin’s idea that species give way to new species through
modifications, and species share common ancestors with one another, which can be traced back
supposedly to one, ultimate common ancestor.
In Chapter twelve of On the Origin of Species, Darwin discusses the geological
distribution of species, mainly those distributed by oceanic islands. Towards the end of the
chapter, he talks about the relationships among species on different islands. He says the fact that
species on certain islands are similar to species on their nearest mainland contributes to the view
of “colonization from the nearest and readiest source, together with the subsequent modification
and better adaptation of the colonists to their new homes.” In Evolutionary Analysis, the
authors discuss mockingbird populations on the Galapagos Islands. The different islands
hosted mockingbirds that were extremely similar to each other but were confirmed by
taxonomists to be of different species. This implies that they were of a common ancestor then
diverged to the different islands and were physically isolated enough to become different species.