Biology
Evolution Basics
Evolution is the slow change in a population’s traits over time. Over long periods, this can lead to new species forming from existing ones.
A population is a group of the same species living in one area.
A species is a group of organisms that can interbreed and produce fertile offspring.
2. Evidence of Evolution
Scientists use multiple types of evidence to support evolution:
Convergent evolution: Different species develop similar traits because they live in similar environments, not because they share a common ancestor.
Vestigial structures: Leftover traits that have little or no function today but were useful in ancestors (like the appendix).
Imperfect structures: Traits that are not well-designed for their current function (like the human eye).
Comparative embryology: Early embryos of different species look similar, suggesting shared ancestry.
Comparative biochemistry: All life shares similar DNA, proteins, and chemical processes.
3. Theories of Evolution
Early scientists had different ideas about how evolution works:
Jean-Baptiste Lamarck believed in use and disuse and that acquired traits could be inherited.
August Weismann proved acquired traits cannot be passed on.
Charles Darwin developed the theory of natural selection and wrote On the Origin of Species.
4. Origin of Life Theories
There are several explanations for how life began:
Intelligent design: Life was created by a higher being.
Panspermia: Life (or its building blocks) came from space.
Chemical evolution: Life formed gradually from simple inorganic molecules to complex organic ones.
5. Fossils and Dating
Fossils are preserved remains of organisms and provide a record of life over time.
Relative dating: Determines age based on rock layers (deeper = older).
Absolute dating: Uses radioactive decay (like carbon-14) to determine exact age.
6. Comparative Anatomy
Comparing body structures helps show evolutionary relationships:
Homologous structures: Same structure, different function → common ancestry.
Analogous structures: Same function, different structure → similar environment.
Divergent evolution: Species evolve differently from a shared ancestor.
7. Natural Selection
Natural selection explains how evolution happens:
Overproduction
Variation
Limited resources
Competition
Survival of the fittest
Reproduction
Speciation or extinction
8. Types of Natural Selection
Stabilizing: Favors average traits
Directional: Favors one extreme
Disruptive: Favors both extremes
9. Adaptations
Adaptations help organisms survive:
Morphological: Physical traits
Physiological: Internal processes
Behavioral: Actions or behaviors
10. Rates of Evolution
Gradualism: Slow, steady change over time
Punctuated equilibrium: Rapid changes in short periods
11. Speciation
New species form through:
Isolation → Genetic changes → Reproductive isolation
Allopatric: Geographic separation
Sympatric: Same location
12. Reproductive Isolation
Prevents species from interbreeding:
Geographic
Ecological
Temporal
Behavioral
Mechanical
13. Genetics and Evolution
Gene pool: All genes in a population
Allele: Different form of a gene
Evolution occurs when allele frequencies change
14. Hardy-Weinberg Principle
Describes when evolution is NOT happening:
Large population
Random mating
No mutation
No migration
If these are met, allele frequencies stay constant.
15. Genetic Changes
Genetic drift: Random changes in genes
Gene flow: Movement of genes between populations
16. Early Earth and Life
Earth is about 4.5 billion years old
Early atmosphere had methane, ammonia, hydrogen, and water vapor
Life likely formed through chemical evolution
17. Key Experiment
The Miller-Urey experiment showed that amino acids can form under early Earth conditions.
18. First Life Forms
First organisms were anaerobic prokaryotes
First photosynthetic organisms were cyanobacteria
19. Eukaryotes
The endosymbiotic theory explains that cells engulfed others and formed organelles like mitochondria.
20. Geologic Time
Cenozoic Era: Age of mammals (current)
Mesozoic Era: Age of dinosaurs
21. Mass Extinction
Dinosaurs likely went extinct due to a meteor impact (supported by iridium evidence).
22. Adaptive Radiation
Rapid evolution of many species after a mass extinction due to open niches.
23. Human Evolution
Key traits: walking upright, intelligence, teeth structure
Origin: East Africa
Homo sapiens have existed for about 50,000 years
What causes speciation?
Speciation happens when populations become reproductively isolated (they can no longer interbreed). This is usually caused by things like:
Geographic isolation (physical barriers like mountains or water)
Behavioral differences (different mating habits)
Genetic changes over time (mutations, natural selection)
2. What is artificial selection?
Artificial selection is when humans choose which organisms reproduce based on desired traits.
Example: breeding dogs for specific features.
3. What is gradualism?
Gradualism is the idea that evolution happens slowly and steadily over long periods of time, with small changes adding up.
4. What is brought about by changes in the frequencies of alleles in a population over many generations?
That is evolution.
5. According to the Hardy-Weinberg Equation, what conditions must occur for evolution NOT to occur?
For a population to stay in equilibrium (no evolution), these 5 conditions must be met:
No mutations
No natural selection (all individuals survive/reproduce equally)
Very large population (no genetic drift)
Random mating
No migration (no gene flow in or out)
Intelligent design (creationism) – relative age of Earth is 6-10,000 years and all life was
placed here by a higher being and haven’t changed since that time
Chemical evolution – from simple inorganic compounds arose simple organic
compounds which led to complex organic compounds; relative age of Earth is 4.5 billion
years and life is constantly changing over time