SBI3U Unit 2: Evolution - Historical Perspective

What is evolution?

A change in inherited traits, or allele frequencies, in a population over generations.

Do individuals evolve?

No. Populations evolve over generations. Individuals are selected.

What is natural selection?

Individuals with helpful inherited traits are more likely to survive and reproduce, so those traits become more common over generations.

What four conditions are needed for natural selection?

Variation, heritability, overproduction of offspring, and differential survival/reproduction.

What causes the struggle for existence?

More offspring are produced than resources can support, so organisms compete to survive and reproduce.

What is variation?

Differences in traits among individuals of the same population.

What is heritability?

The ability of a trait to be passed from parents to offspring.

What is fitness in evolution?

Reproductive success: producing surviving offspring that can also reproduce.

What is an adaptation?

An inherited trait that increases fitness in a specific environment.

What is a selective pressure?

Any environmental factor that makes some inherited traits more helpful or harmful than others.

Does natural selection give organisms traits because they need them?

No. Variation exists first. Natural selection changes how common traits become.

What is common ancestry?

The idea that different species are related because they descended from shared ancestors.

What is an evolutionary tree?

A branching diagram showing how species are related through common ancestors.

What did early Greek thinkers contribute to evolution?

Thales proposed natural explanations for life; Anaximander suggested organisms changed over time; Empedocles suggested better-suited organisms survived more often.

What was preformation?

The incorrect belief that organisms already existed as tiny, fully formed versions inside eggs or sperm.

What was Lamarck’s theory?

Organisms changed through use and disuse and passed acquired traits to offspring. Species change was an important idea, but his inheritance mechanism was incorrect.

What did Malthus contribute?

Populations produce more offspring than can survive, creating competition for limited resources.

What did Lyell contribute?

Uniformitarianism: slow geological processes shape Earth over a very long time; Earth is old enough for gradual evolution.

What did Wallace contribute?

He independently proposed natural selection acting on variation and pushed Darwin to publish his theory.

What did Darwin contribute?

He explained the mechanism of evolution: natural selection acts on inherited variation.

Darwin vs. Lamarck?

Lamarck: acquired traits are inherited. Darwin: inherited variation already exists, and natural selection changes trait frequencies.

How do fossils support evolution?

They show extinct organisms, change over time, and transitional forms linking past and present organisms.

What are homologous structures?

Similar underlying body structures inherited from a common ancestor, even when their functions differ.

What are analogous structures?

Structures with similar functions but different evolutionary origins. They show convergent evolution, not close ancestry.

What are vestigial structures?

Reduced inherited structures that have lost most or all of their original function.

How does DNA support evolution?

Species with more similar DNA or protein sequences usually share a more recent common ancestor.

How does biogeography support evolution?

Species in nearby geographic areas are often closely related because they share common ancestors.

What is mutation?

A random change in DNA that creates new alleles. Mutation is the original source of new genetic variation.

What is gene flow?

Movement of alleles between populations through migration and reproduction.

What is genetic drift?

Random change in allele frequencies, especially important in small populations.

What is the bottleneck effect?

A population is drastically reduced, leaving less genetic diversity in the survivors.

What is the founder effect?

A small group starts a new population and carries only part of the original population’s genetic variation.

What is sexual selection?

Selection based on traits that improve mating success, even if the traits do not directly improve survival.

What is artificial selection?

Humans deliberately breed organisms for desired traits.

One benefit and one risk of artificial selection?

Benefit: improved yield, disease resistance, or useful traits. Risk: reduced genetic diversity, inbreeding, or harmful inherited traits.

How can environmental change affect natural selection?

It changes selective pressures. Traits that were helpful before may become harmful, and different traits may become advantageous.

Why is genetic diversity important for endangered species?

More variation gives a population a better chance of surviving disease, climate change, and environmental stress.

Independent vs. dependent variable?

Independent variable = factor changed. Dependent variable = factor measured.

What are controlled variables?

Conditions kept the same so a test is fair.

Reliability vs. validity?

Reliability = results are consistent when repeated. Validity = the investigation tests what it claims to test.

Correlation vs. causation?

Correlation means two variables are associated. Causation means one variable directly causes the change.

What should a strong scientific conclusion include?

A claim, specific data evidence, scientific explanation, and limitations/errors if relevant.

Genetic drift vs. natural selection?

Genetic drift changes allele frequencies by chance. Natural selection changes allele frequencies because some inherited traits improve reproductive success.

How does the fossil record support evolution?

Fossils show extinct organisms, changes in species over time, and the order that life forms appeared and disappeared.

Relative dating vs. radiometric dating?

Relative dating compares rock layers to tell older from younger. Radiometric dating uses radioactive decay to estimate an actual age.

Why do vestigial structures support evolution?

They are reduced inherited structures, such as whale pelvic bones or ostrich wings, showing descent from ancestors in which the structure had a larger function.

Directional selection?

One extreme trait is favoured, so the population shifts toward that extreme.

Stabilizing selection?

Middle traits are favoured, while both extremes are selected against.

Disruptive selection?

Both extreme traits are favoured, while the middle trait is selected against.

Divergent evolution?

Related populations become more different as they adapt to different environments.

Convergent evolution?

Unrelated species become more similar because they face similar selective pressures.

Parallel evolution?

Similar species independently evolve similar traits during a similar time because of similar selective pressures.

Coevolution?

Two closely interacting species evolve in response to each other, such as flowers and pollinators or predators and prey.

What is a species?

A group whose members can naturally interbreed and produce viable, fertile offspring.

What is speciation?

The formation of one or more new species when populations become reproductively isolated long enough to evolve separately.

Pre-zygotic barrier?

A barrier that prevents mating or fertilization before a zygote forms, such as geographic, behavioural, ecological, or timing differences.

Post-zygotic barrier?

A barrier after fertilization. A hybrid may be unhealthy, unable to survive, or sterile, like a mule.

Allopatric speciation?

A physical geographic barrier splits a population, such as a river, mountain, glacier, or island separation.

Peripatric speciation?

A small population becomes isolated at the edge of the original population’s range and evolves separately.

Parapatric speciation?

Adjacent populations experience different selective pressures and gradually become reproductively isolated, even though their ranges touch.

Sympatric speciation?

A new species forms in the same geographic area because of reproductive, ecological, or behavioural isolation.

Gradualism?

Evolution occurs slowly and continuously through many small changes over long periods of time.

Punctuated equilibrium?

Species stay mostly unchanged for long periods, then undergo relatively rapid evolutionary change during speciation. It does not mean evolution happens instantly.

Who proposed punctuated equilibrium?

Stephen Jay Gould and Niles Eldredge.