1. UNIT 6: Evolution and Classification
Chapter 10
Principles of Evolution

2. Ch. 10.1 Early Ideas About Evolution
Early ideas set the stage for Darwin’s theory
Early scientists proposed many ideas.
George Cuvier (anatomist) promoted the idea of catastrophism – the idea that sudden geologic catastrophes caused the extinction of large groups of organisms.
Charles Lyell (geologist) shared Cuvier’s ideas but thought geologic processes always work the same - uniformitarianism.

3. Ch. 10.1 Early Ideas About Evolution

4. Ch. 10.1 Early Ideas About Evolution
Jean Baptiste Lamarck (biologist) proposed that individual organisms could acquire traits during their lifetimes as a result of experience or behavior; “inheritance of acquired characteristics”. Rejected by scientific community

5. Ch. 10.2 Darwin’s Observations
Darwin’s Voyage
In 1831, the HMS Beagle set sail from England to map the coast of South America & Pacific Islands.
Charles Darwin was hired to travel with the captain and observe the land and its inhabitants along the way.
Darwin read Lyell’s Principles of Geology and found evidence supporting his ideas. Darwin started forming his own ideas… about evolution.
However, Alfred Russel Wallace was also coming up with similar ideas about evolution at the same time.

6. Ch. 10.2 Darwin’s Observations
“Descent with Modification”
Darwin used this phrase to describe the process of evolution.
He reviewed evidence that every species must have descended by reproduction from preexisting species.
These species were able to change over time.
He was the first to argue that all species descended from one or only a few original kinds of life.

7. Ch. 10.2 Darwin’s Observations
The Galapagos Islands
Darwin saw the animals of the Galapagos Islands as evidence of descent with modification.
13 similar species of finches, all with different beaks adapted for different foods.
Many similar species of tortoises adapted to feeding on different vegetation or in different terrain.

8. Ch. 10.2 Darwin’s Observations

9. 10.3 Theory of Natural Selection
Darwin’s Theory of Natural Selection
Darwin proposed that natural selection was the mechanism for descent with modification.
He considered what sort of environmental pressures would cause changes in organisms over time.

10. 10.3 Theory of Natural Selection

11. 10.3 Theory of Natural Selection
Overproduction: Drawing from economist Thomas Malthus, Darwin knew populations can increase more quickly than food supplies.
Populations are limited by conditions of their environment (food, predators, disease, geography).
So not all offspring live very long.
Darwin realized that the environment limits the populations of all organisms by causing deaths and limiting births.

12. 10.3 Theory of Natural Selection
Variations: In any population, individuals have different traits (size, color, strength, speed, ability to find food, resistance to disease, etc.).
These variations can be inherited by offspring.
Occasionally new traits appear in the population.
Traits that increase an individual’s ability to survive may be passed on to offspring.

13. 10.3 Theory of Natural Selection
Adaptation: Individuals must compete in the “struggle for existence”, where some variations improve the chance to survive and reproduce and other variations reduce this chance.
Variations that improve an individual’s chances to survive are called adaptations.

14. 10.3 Theory of Natural Selection
Descent with Modification: Darwin concluded that organisms with the best adaptations are most likely to survive and reproduce.
Through inheritance, those adaptations become more frequent in the population.
Populations may begin to differ as the adapt to different environments, even if they descended from a common ancestor.
This conclusion is the core idea of Darwin’s theory.

15. 10.3 Theory of Natural Selection
“Survival of the Fittest”
Darwin sometimes used this phrase to describe the struggle for existence/survival.
It does not mean “the fastest, strongest, biggest” survives!
Fitness is the measure of an individual’s hereditary contribution to the next generation.
A “fit” individual is one that has offspring that also live long enough to reproduce in a given environment.

16. 10.4 Evidence of Evolution The Fossil Record
Superposition is the geologic principle that states if the rock strata (layer) has not been disturbed, the lowest stratum was formed before the strata above.
A fossil found in a lower layer will be older than one found in a higher layer.
Using this principle we can infer:
Different organisms lived at different times.
Today’s organisms are different from those in the past.
Fossils found in adjacent layers will be more similar.

17. 10.4 Evidence of Evolution Anatomy and Embryology
Looking at the bones in the forelimbs of humans, penguins, alligators, and bats shows they all share a common theme.
1 bone (humerus), 2 bones (radius & ulna), small bones (carpals & metacarpals), many bones (phalanges).

18. 10.4 Evidence of Evolution Anatomy & Embryology (contd.)
Homologous Structures: are features that are similar in structure but appear in different organisms.
Analogous Structures: perform similar functions, but are not similar in origin.
Example: Bats and dragonflies both have wings to fly, but the structures of each are very different.

19. 10.4 Evidence of Evolution

20. 10.4 Evidence of Evolution
Analogous Structures

21. 10.4 Evidence of Evolution
Vestigial Structures: “transitional structures” or remnants of organs or structures that had a function in an early ancestor.
Example: the human coccyx, or “tailbone”, is made of four fused vertebrae that resemble bones in an animal’s tail. Other examples include pelvic bones in whales and the human appendix.