Ch 04 Origins of Life/ Natural Selection

Ch 04 Section 1Section 2

Animation: Stanley Miller’s Experiment

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Variety ofmulticellular

organismsform, firstin the seasand lateron land

Biological Evolution(3.7 billion years)

Chemical Evolution(1 billion years)

Small organic

moleculesform inthe seas

Large organic

molecules form in the seas

First protocells

form in the seas

Single-cell prokaryotes

form in the seas

Single-celleukaryotes

form inthe seas

Origins of LifeOrigins of Life

First was Formation of the earth’s early crust and atmosphere

Then

Then PLAY

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How Do We Know Which Organisms Lived in the Past?

4. Our knowledge about past life comes from fossils, chemical analysis, cores drilled out of buried ice, and DNA analysis.

Figure 4-4Figure 4-4

B. Natural Selection and Adaptation1. Evolution is the change in a population’s

genetic makeup over timea) Populations evolve by becoming genetically

differentb) All species descend from earlier, ancestral

species2. Microevolution describes the small

genetic changes that occur in a population over time

3. Sexual reproduction leads to random recombination of alleles from individual to individual

Natural Selection

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Gene Flow or MigrationGene Flow or Migration

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4. Over time, a population’s gene pool changes when mutations in DNA molecules are passed on to offspring.

a) Mutations are random changes in the structure/number of DNA molecules in a cell.

b) Mutations occur in two ways.• Gene DNA is exposed to external agents like X rays,

chemicals (mutagens) or radioactivity.

• Random mistakes that occur in coded genetic instructions.

c) Only mutations in reproductive cells are passed to offspring.

d) Many mutations are neutral, some are deadly; a few are beneficial.

5. For natural selection to evolve in a population, three conditions are necessary:

a) The population must have genetic variability.b) The trait must be heritable, capable of being

passed from one generation to another.c) The trait must enable individuals with the trait

to produce more offspring than individuals without the trait; this is differential reproduction.

6. Adaptations are heritable traits that help organisms to survive and reproduce better under prevailing environmental conditions.

7. Environmental changes require adaptations also. Organisms must:

a) Adapt to the new conditions.

b) Migrate to an area with more favorable environment.

c) Organisms that cannot adapt become extinct.

Animation: Moth Populations

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8. Coevolution is the interactions of species will cause them to engage in a back and forth genetic contest in which each gains a temporary genetic advantage over the othera) This often happens between predators and

prey species.

9. Hybridization can occur when individuals off two distinct species crossbreed to produce fertile offspring.

a) New species can arise. [ i.e. dog breeds]10. Horizontal gene transfer is when species (mostly

microorganisms) exchange genes without sexual reproduction

11. A population’s ability to adapt to new environmental conditions through natural selection is limited by its existing genes and how fast it can reproduce.

a) Humans have a relatively slow generation time (decades) and output (# of young) versus bacteria which can reproduce millions in hours!

Horizontal Gene Transfer

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12. Common myths about evolution through natural selection.

a) Natural selection can only act on existing genes and is limited by reproductive capacity.

b) There is no such thing as genetically perfect organism; the purpose is to leave the most descendants