Evolution and Natural Selection
Grade 10 · Science · Study Guide
Discover how life on Earth has changed over billions of years through the mechanisms of evolution and natural selection.
Evolution is the change in the inherited traits of a population over successive generations. Charles Darwin's theory of natural selection, proposed in 1859, provides the primary mechanism for evolution. Natural selection occurs when individuals with heritable traits that improve survival and reproduction pass those traits to offspring at higher rates, gradually changing the makeup of the population.
Darwin identified four key components of natural selection: variation (individuals within a population differ in their traits), heredity (traits are passed from parents to offspring), differential reproductive success (some traits lead to better survival and reproduction), and overproduction (populations tend to produce more offspring than can survive). Together, these components mean that advantageous traits become more common over time — the population evolves.
Evidence for evolution comes from multiple independent sources: the fossil record (showing change over time), comparative anatomy (homologous structures in different species showing common ancestry), embryology (similar developmental stages in related species), biogeography (distribution of species related to geography), and molecular biology (DNA similarities between related species). Speciation — the formation of new species — occurs when populations become reproductively isolated and diverge over time.
| Evidence Type | What It Shows | Example |
|---|---|---|
| Fossil record | Change in species over time | Progression of horse fossils |
| Homologous structures | Common ancestry | Human arm, whale flipper, bat wing |
| Molecular biology | DNA similarity between related species | 98% DNA similarity: humans and chimps |
| Biogeography | Species distribution matches geography | Marsupials concentrated in Australia |
| Embryology | Similar early development in related species | Fish and human embryos look alike early on |
Key terms
- Natural selection
- The process by which individuals with favorable heritable traits survive and reproduce more successfully.
- Adaptation
- A heritable trait that increases an organism's fitness (survival and reproductive success) in its environment.
- Fitness
- An organism's ability to survive and reproduce in its environment; the measure of evolutionary success.
- Speciation
- The formation of new and distinct species through evolutionary processes, often involving reproductive isolation.
- Homologous structures
- Anatomical structures in different species that share a common evolutionary origin, even if they now serve different functions.
- Fossil record
- The collection of all known fossils; provides evidence of how life has changed over geological time.
Flashcards
- Evolution
- The change in heritable traits of a population over successive generations.
- Variation
- Differences in traits among individuals in a population; raw material for natural selection.
- Reproductive isolation
- When populations can no longer interbreed; leads to speciation over time.
- Vestigial structure
- A structure that has lost its original function through evolution (e.g., human tailbone, whale hip bones).
- Common ancestor
- An ancestral species from which two or more modern species descended.
- Genetic drift
- Random changes in allele frequencies in a population, especially pronounced in small populations.
Practice questions
Which of the following is NOT a component of Darwin's natural selection?
- Variation in traits
- Heredity of traits
- Deliberate adaptation by organisms
- Differential reproductive success
Show answer
Answer: Deliberate adaptation by organisms
Natural selection is not intentional — organisms do not 'choose' to adapt. It operates on random heritable variation; individuals don't change to suit their environment.
Homologous structures in different species provide evidence of common ancestry.
Show answer
Answer: True
Homologous structures (like the bones in human hands, whale flippers, and bat wings) share the same basic bone structure, indicating descent from a common ancestor.
The formation of a new species through evolutionary processes is called ___.
Show answer
Answer: speciation
Speciation occurs when populations become reproductively isolated (geographically, behaviorally, or genetically) and diverge enough to be considered separate species.
A population of beetles lives on green leaves. A random mutation produces some brown beetles. Birds eat the brown ones more easily. Over time the population becomes mostly green. This illustrates:
- Genetic drift
- Natural selection
- Artificial selection
- Mutation only
Show answer
Answer: Natural selection
The brown beetles have lower survival due to predation — a form of selection pressure. Green coloration is a favorable adaptation; over generations, the green trait becomes more common.
Evolution can occur in a single generation.
Show answer
Answer: False
Evolution describes changes in allele frequencies across generations in a population — it occurs over many generations, not within a single individual's lifetime.
Fun facts
- Humans and chimpanzees share about 98.7% of their DNA — and we're more closely related to chimps than chimps are to gorillas.
- Darwin was initially reluctant to publish his theory and only did so after Alfred Russel Wallace independently developed the same idea.
- The peppered moth is a classic real-world example of natural selection: dark-colored moths became more common in industrial England as pollution darkened tree bark.
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