Unit 3: Evolution
Lesson 4: Evidence for Evolution
There were many forms of evidence that convinced Darwin of the evolution of species and enabled him to formulate his theory of evolution by means of natural selection.
Evidence 1:
Biogeography: is the scientific study of the geographic distribution of organisms based on both living species and fossils.
Observations:
Darwin noticed that isolated islands had many species that were found nowhere else, yet resembled species that lived on the mainland.
Many species on the islands were fearless.
There are no native amphibians or mammals with the exception of bats and sea lions on the
Galapagos; only birds and reptiles.
Hypotheses:
Animals migrated to the island from the mainland and then evolved based on the environment of the island.
Since animals on the island do not have any natural predators, they lost their instinctive fear
Amphibians and mammals are unable to cross an open ocean to reach a remote island
Counter-example:
What if the reason there are no amphibians and mammals on the island is because they cannot survive such conditions? How would we test this? Well, if you introduce non-native species to the island, then you can see if they can survive or not. In fact, when rats, dogs, and pigs were introduced to certain Hawaiian islands, they survived quite well and wreaked havoc on the native island-dweller species, sometimes forcing it to extinction.
Evidence 2:
Homologous and Analogous Features:
Homologous Features: a structure with a common evolutionary origin that many serve different functions in modern species (ex: bat wing versus a human arm). In addition, all mammals have precisely
28 skull bones and 7 neck bones, regardless of the size of their skull or length of their necks.

Closely related species had homologous features because they shared a common ancestor. Over time, original structures were modified as each species evolved. Closely related species share homologous development processes and patterns as well. In early development stages, the embryos of all vertebrates, including humans, chickens, and fish, all posses a short bony tail. Human embryos also have gill slits even though, by the time we were born, we do not have gills.

Analogous Features: a structure that performs the same function as another but is not similar in origin or anatomical structure; for example, bird and insect wings and eyes
Evidence 3:
Vestigial Features: a rudimentary and non-functioning, or only marginally functioning, structure that is homologous to a fully functioning structure in closely related species.
Other examples of vestigial features:
Dogs, pigs, horses have a vestigial toe – a toe that does not touch the ground
Large snakes and whales have vestigial hip bones
Human goosebumps when we are cold or scared/threatened; goosebumps occur as the result of tiny muscles under the skin surface contracting and lifting up the hair. In mammals with thick hair/fur, lifting up the hair provides warmth for the animal and also makes the animal look big when threatened.
Evidence 4:
Competition within Populations
Populations could not grow indefinitely. All populations were limited in size by their environment – and in particular their food supply. Many species produce large numbers of offspring, but not all survive. There is a limit to the size of a population that an environment can support. The result is competition between members of the same species.
Consider a population of 1000 robins that returns to Ontario in the spring. These 1000 robins form breeding pairs that may lay two or three batches of eggs each summer. If they all hatched and survived, the robin population would jump from 1000 in the spring to more than 5000 by the end of the summer.
Of these 5000 robins, only about 1000 will return the next spring. Under these conditions, only one out of every five robins survive each year.