Happy Birthday Mr. Darwin

What concepts did Darwin develop, and why were they so revolutionary?

Species can change- Living things are not fixed, but can change over many generations.

Common Descent—All life on Earth shares a common ancestry. Yes, even humans.
Drawing from one of Darwin's notebooks

Gradualism--The change of a species takes a long time.
Marine Iguana, Isabela Island, Galapagos

Land Iguana, North Seymour Island, Galapagos.
The land iguana and marine iguana evolved from a common ancestor, probably an iguana from the mainland of South America.

Natural selection
Certain randomly acquired traits are helpful.

Individuals with helpful traits survive longer, have more offspring, so over time these traits increase in a
population.

Nature selects which traits are beneficial, and which are not.

Small ground finch, San Cristobal Island, Galapagos

Medium ground finch, San Cristobal Island, Galapagos.

The main difference between "Darwin's finches" is the size and shape of their bills. What advantage would their be to an individual with a beak like the one found on the medium ground finch? What about the the bill found on the small ground finch?

Others prior to Darwin had suggested species may have changed over time, and were not fixed. However, Darwin was the the first to suggest a logical mechanism (natural selection) though which these changes occurred.