Chapter 16Darwinian Evolution

What is evolution?A theory that states species slowly change over time through the process of natural selection.

What is a theory?A hypothesis that is supported with a lot of scientific evidence.

Who was Charles Darwin?1. British2. Lived in the 1800s

- born on same day as Abe Lincoln3. Born into a reasonably wealthy family

- dad was a doctor & very overbearing

4. Originally went to college to be a doctor, but didn’t like the blood & screaming of 19th century surgery (no anesthesia)

5. Dad forced Charles to become a minister, but Darwin really wanted to be a naturalist

- he continued to study nature on the side while in theology school

6. When Charles graduated, he took a job as a naturalist on the H.M.S. Beagle which was taking a 5-year voyage around the world.

- Dad was not happy

Darwin’s Journey on the Beagle:

Darwin’s Journey on the Beagle:1. Charles was a good scientist

- he collected lots of specimens- he wrote down a lot of notes

2. What 3 patterns of biodiversity did Darwin observe on his voyage?Species Varied GloballySpecies Varied Globally

Different, yet ecologically similar, animal species inhabited separated, but ecologically similar

habitats. He wondered, how this could happen? Species Varied LocallySpecies Varied Locally

Different, yet related, animal species often occupied different habitats within a local area.

Species Varied Over TimeSpecies Varied Over TimeSome fossils of extinct species were similar to

living species.3. The Galapagos Islands

- Located 500 miles off the coast of South America near the equator- Each island has different climates & habitats- Darwin noticed that similar species on different islands had special adaptations to survive in those habitats- His studies of their finches & tortoises impacted him greatly

4. Based on observations made on this trip, Darwin came up with his theory of

evolution by natural selection

1. Bishop Ussher (1581-1656)

- using the Book of Genesis, he calculated that the universe was created on October

23, 4004 B.C.- later theologians calculated that this

began at 9:00 am London time; midnight Garden of Eden time

- in Darwin’s day, most Europeans believed

this.

2. James Hutton & Charles Lyell- Both were geologists- Hutton stated that the Earth is much

older than Ussher believed (deep time), and that there were different processes that shaped the earth as we know it.

- Lyell stated that the phenomena that shaped the world millions of years ago continue to occur today. He also stated that the laws of nature are constant & that we must explain past events through observations made in the present. Lyell called this concept uniformitarianism.

- Darwin felt that if geology could change like this, life could too.

3. Jean Baptist-Lamarck- French naturalist- proposed a theory of evolution- His mechanism was wrong:

A. Tendency towards perfection- organisms are continually changing that help them

live betterB. Selective use & disuse

- this is what allows the organism to change

C. Inheritance of acquired traits- a body builder could pass on his

big muscles to his son

4. Thomas Malthus (1766-1834)

- English economist- In a 1798 essay, he

stated that if the human population continues to grow unchecked, we will eventually run out of resources.

- Darwin recognized that this would be even more true in nature because nature produces more young and resources are even more

limited.

What is a theory?A hypothesis with lots of empirical (scientific) evidence. It may also be to as a statement that unifies many related hypotheses into a single statement.

What is evolution?1. Change in the genetic makeup of a species over time2. This can lead to the creation of a new species

Why did Darwin wait 23 years to present his idea?

1. It challenged fundamental scientific beliefs.

2. As a trained theologian, he was stunned & disturbed by them.

3. He knew it would create a firestorm of opposition.

What prompted Darwin to publish his idea?

1. He received a letter from a fellow scientist named Alfred Wallace.

2. Wallace was proposing a similar hypothesis.3. Darwin wanted to make sure he would get

the proper credit for his work.

What is the name of Darwin’s famous book?Origin of Species by Means of Natural Selection

- Origin of Species for short

- published in 1859 (151 years ago)

- 1st printing sold out in the first day- current Amazon.com rank: 2300/420000+ (inside the top 1% in

sales)

What is inherited variation?The natural variation of phenotypes within a population.

What is artificial selection?1. Humans choose which of the natural

variations are to be passed on to the next generations.

2. These traits may not actually improve fitness. (Fitness = survive & reproduce)

Evolution by Natural Selection:

1. Struggle for Existence- high birth rates & limited

resources lead to competition

- this concept shows the influence of Malthus

Evolution by Natural Selection:2. Survival of the Fittest – those with the best

adaptations survive & reproduce

Fitness – ability to survive & reproduceAdaptation – inherited characteristic that

increases fitness

Adaptations can be:A. Anatomical/StructuralB. Physiological (life’s chemical

processes)C. Behavioral

What is the relationship between adaptations & fitness?

Adaptations increase fitness

Evolution by Natural Selection:3. Descent with Modification

A. Natural selection, over time, produces organisms that have different structures, occupy different niches, & live in different habitats.

B. Implies that all organisms are related to each other because they inherited the adaptations from their ancestors.

Evolution by Natural Selection:4. Common Descent

- All species arose from a common ancestor.

- a.k.a. the “Tree of Life”

1. The Fossil Record- Fossils show the transitions

of species during evolution

2. Similarity in Anatomy – related species have similar anatomy

Man-Gorilla-Chimpanzee-Orangutan-Gibbon

2. Similarity in Anatomy continued:What is a homologous structure?

A. Developed from the same embryonic tissue.B. Created by divergent

evolution.* The only way that this could happen is that the species must be related.

2. Similarities in anatomy continued:What are analogous structures?

A. Similar structures that don’t come from the same embryonic tissue.

B. Created by convergent evolution.C. Similar habitat created the

evolutionary pressure that led to the similar structures.

* For example, the analogous structures of sharks & dolphins suggests that they are not closely related.

2. Similarities in anatomy continued:What are vestigial organs/structures?

A. Homologous structures that are small & unused.

B. They are evolutionary leftovers & they give a hint to what the common

ancestor was like.

3. Similarities in Embryology

Closely related species share common embryology.

4. Similarities in DNA bases sequences & amino acid sequencesmore similarities = closely related * diverged from common ancestor more recently

fewer similarities = less closely related

* diverged from common ancestor a long, long time ago

H = Human

C = Chimp

The DNA of chimps and humans is 98.4% identical.