Natural Selection

Thirteen topics on evolution — the unifying idea of biology. What natural selection actually is (and the myths it isn't), the modes of selection that reshape a trait, artificial selection as the same mechanism in human hands, the population genetics of allele pools and the difference between genetic drift and selection, Hardy-Weinberg equilibrium and its math, the many independent lines of evidence of evolution, common ancestry and how to read a phylogeny, continuing evolution you can watch in antibiotic resistance, how speciation and extinction shape diversity, why variation is the raw material for adaptation, and the separate question of the origin of life on Earth.

Topics

7.1

Introduction to Natural Selection

Natural Selection

Artificial Selection

Population Genetics

Hardy-Weinberg Equilibrium

Evidence of Evolution

Common Ancestry

Continuing Evolution

Phylogeny

Speciation

Extinction

Variations in Populations

Origin of Life on Earth

Lesson

Diag

locked

Key relationships The Hardy-Weinberg math and the conditions behind it

Allele frequencies

$$p + q = 1$$

p and q

p = frequency of the dominant allele, q = frequency of the recessive allele (these are allele frequencies)

Genotype frequencies

$$p^2 + 2pq + q^2 = 1$$

What each term is

$$p^2$$ = homozygous dominant, $$2pq$$ = heterozygous, $$q^2$$ = homozygous recessive

Working backward

the recessive phenotype gives $$q^2$$, so $$q=\sqrt{q^2}$$, then $$p = 1 - q$$; heterozygotes = $$2pq$$

Five HW conditions

no mutation, random mating, no gene flow, a large population (no drift), and no selection

What HW describes

a non-evolving population — the conditions are not arbitrary; a deviation from them is exactly what causes allele frequencies to change (evolution)

Natural selection

acts on existing heritable variation and shifts allele frequencies across generations — it does not create the variation

Drift vs selection

drift = random change in allele frequency (strong in small populations); selection = non-random, fitness-based change

Unit 7 tools

Challenge bank

1 / 60

60 open-ended problems.

Read the question, work it out, then flip the card to compare your reasoning to the worked solution. Mark each card so you can return to the ones that still bite.

Question

Tap card to reveal explanation

Worked solution

Tap card to return to question

Cumulative assessment

Test the unit.

Twenty mixed items pulled from across all 13 topics. Identifies which misconceptions still bite when you cannot see which topic the question came from.