Descent With Modification: A Darwinian View of Life Campbell Chapter 22

What Evolution Is Descent with modification Change in genetic frequencies over time Change with inheritance From

What Evolution Isn’t It is not a theory that says humans came from apes!

Historical Context of Evolution People have always wondered about the origin of diverse life forms on Earth.

Aristotle and Scala Naturae Aristotle believed that there was a Divine Creator at the top of a ladder, and everything else descended from that being. From

Carolus Linnaeus Created a system of taxonomy that did not show relationships between organisms.

Georges Cuvier Observed changes in fossil layers of rock Surmised that layers were different due to catastrophes (floods, ice ages)

Lamarckian View of Evolution

What Lamarck Observed More modern fossils were found in upper layers of rock This led to the formation of more modern species

Use and Disuse Body parts used to get along in the environment get stronger and larger Those that aren’t used, deteriorate.

Inheritance of Acquired Characteristics Modifications acquired during an organism’s lifetime could be passed on to their offspring.

Dispelling the myths Neither of these things were possible because they were missing a very important component…

Darwinian View of Evolution

Grew up very wealthy, educated Was a med student, then a divinity student Served as a naturalist for British government on the HMS Beagle Darwin backgrounder

Where Darwin Went

Development of Theory of Natural Selection Darwin observed 12 species of finches Noted differences in beaks and how that correlated to food choice

What Darwin noticed Organisms on the South American continent looked like those on the Galapagos but didn’t live anywhere else Was influenced by Lyell (Principia Geologica)

Descent with Modification Supposed that all organisms were related to an ancient ancestor

Natural Selection After studying specimens he collected, analyzing data and reading an essay by Thomas Malthus, Darwin formulated a theory that explained how different species originated.

Tenet #1 Variation exists among members of a species.

Tenet #2 This variation is inherited.

Tenet #3 There are limited resources in the environment. There is a struggle for survival.

Tenet #4 Organisms with favorable traits are more fit, thus they leave behind more offspring than those who are less fit.

Tenet #5 These favorable traits persist in the population and will become more frequent.

Result: Differential reproductive success leads to change in favorable traits among generations

In sum… Natural selection occurs as a result of interactions between the environment and the genetic variability demonstrated in living organisms. It is the result of differential reproductive success.

Artificial Selection Organisms with certain traits are bred repeatedly until population has only that trait Dog breeds are another good example

Other Evidence for Evolution There is other evidence that evolution has occurred: Anatomical Molecular Fossil Record Biogeography Fossil of Archaeopteryx, ancient bird

Homologous Structures

Vestigial Structures Structures which are smaller or reduced in size because they are no longer used/needed Whale pelvis Vestigial legs on snakes Human appendix

Embryological Similarities Presence of post-anal tail, pharyngeal gill slits indicates common ancestry What else does it indicate?

Molecular homologies Amino acid sequences among vertebrates have similarities What else is similar?

Fossil Record Transitional forms show the change from simpler forms to more complex forms

Biogeography Geographic distribution of species Similar species live in the same area