1. Descent with Modification19
Descent with Modification 1

2. Concept 19.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species

3. Brief History: What did people think about life on Earth 300 years ago?
Science doesn’t happen in a vacuum.
Darwin did not develop his thoughts/theories on evolution on his own.
He was influenced by many other sources.
Lots of people were thinking about life.
Had it always existed as it does now?
Was it always changing?
How old is the Earth? (Bible estimates ~7000 yrs)
What do all these fossils mean?

4. Influences on Darwin Thomas Malthus Georges Cuvier
“Essay on the Principle of Population” (1798)
Populations would grow forever, but they don’t because of competition for limited resources.
Georges Cuvier
Fossils are remains of extinct life forms.
“Catastrophism” (~1800)
Fossil boundaries represent catastrophes (flood, drought, etc.) that destroyed much life at once.

5. Influences on Darwin James Hutton Charles Lyell
Profound changes in Earth can result from cumulative effects of slow but continuous processes.
“Gradualism” (1795)
Charles Lyell
Geologic processes happening on Earth now are similar to those in the past.
“Uniformitarianism” (1830)
Earth is VERY OLD; millions, rather than thousands of years.

6. Influences on Darwin Jean Baptiste Lamarck
One of the first evolutionists.
“Inheritance of Acquired Characteristics” (1809)
Right about the theory (evolution), wrong about the mechanism (use and disuse).

7. Darwin: Brief Biography (1809-1882)
Unspectacular young life.
Comfortable family wealth.
Undecided about a career (med school, parsonage, naturalist).
Family connections got him a spot aboard the HMS Beagle in 1831.
5 year voyage.
Circumnavigation of the globe.
Served as a “naturalist”.
Read, collected specimens, wrote, and thought.

8. Galapagos Islands An important stop for Darwin.
Noticed many weird, unique animals.
The “A-ha! Moment”.
Marine Iguanas—the only swimming lizard in the world
Giant Tortoises—all 1 species; different shell shapes due to different cactus plants per island
Finches—there are 12 species of Galapagos Finch; different beak structure driven by different feeding behavior; all share a common immigrant finch ancestor

9. Post Voyage
Darwin came home, published his journal, got married, had kids, did lots of other work…but, did not publish his theory for 20 years!
Then, he received a paper to review from Alfred Wallace (1858).
Wallace’s paper outlined a new “theory” that was just like Darwin’s!
So, Darwin wrote his own paper and published a book:
“On The Origin of Species By Means of Natural Selection”
One of the most important books ever published in Biology.

10. Concept 19.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life

11. Ideas from The Origin of Species
Darwin explained three broad observations about life
The unity of life
The diversity of life
The match between organisms and their environment

12. Darwin’s Theory of Evolution
2 Big Ideas:
Natural Selection
Descent With Modification

13. Natural Selection How It Works:
Overproduction of offspring is characteristic of most species.
Most babies won’t grow up.
Variation exists among individuals in a population.
No 2 are quite the same.
Competition develops for limited resources.
The “struggle for existence”.

14. Clarification—Individuals do not evolve, populations do!
Successful competitors survive, reproduce, and pass on their traits (differential reproductive success)
“Survival of the Fittest!”
Repeat steps 1-4 for many, many generations (millions of years) and life will adapt to the environment.
Clarification—Individuals do not evolve, populations do!

15. Examples of Natural Selection
Artificial Selection
Human selection of desired traits; can lead to big changes very quickly.
The Galapagos Finches
Pesticide Resistance
Tons of other examples generated by modern science over the past 150 years.
See your book for details.

16. Descent With Modification
Also known as “Common Ancestry of Life.”
A fundamental conclusion of natural selection.
If we accept that life evolves, then logic suggests that all of life shares a common ancestor.
This is supported by much evidence we have found.
Example—structural similarities between skeletons of closely related primates and between fossils and modern organisms.

17. Importance of the Theory of Evolution
Scientifically, evolution is the unifying principle of all other fields of biological study.
It explains similarities and differences in life.
“Nothing in Biology makes sense except in the light of evolution.”
-Theodusius Dobzhansky, March 1973
(Geneticist, Columbia University)