Chapter 2 and Lecture 2 - Darwin's Big Idea and How It Changed Biology

What were the two open questions in biology before Darwin?

Where do species come from?; How do we explain complex adaptations with clear function?

What was the dominant explanation for adaptation before Darwin?

The argument from design: organisms' purposeful traits were thought to reflect God's creation

Who was William Paley and what was his argument?

Anglican theologian. He argued that complex adaptations (like a watch) imply a designer (God). This analogy suggested that organisms, like machines, require a creator

What was David Hume's critique of Paley's argument?

He showed the analogy between machines and organisms is logically flawed — appearance of design doesn't prove actual design

If we found a highly complex molecular machine in a cell (like ATP synthase), how would Paley vs. Darwin interpret it?

Paley → evidence of a divine designer; Darwin → product of natural selection over time

Who was Jean-Baptiste Lamarck and what was his evolutionary idea?

First to use the term "evolution." Proposed the inheritance of acquired characteristics — traits modified in an organism's lifetime could be passed on

Example Lamarck used?

Giraffe neck elongation from stretching daily, passed on to offspring

Why was Lamarck wrong?

Weismann's germplasm theory (1889): only germ cells (gametes) carry heredity. Somatic changes (body changes) aren't inherited

What is the modern molecular interpretation of why Lamarck was wrong?

Genetic information flows one way: DNA → protein, never reversed. Soma → gamete transfer is impossible

If a bodybuilder has a child, will the child be born muscular?

No — somatic changes don't affect germline DNA (Weismann's principle)

What two themes define Darwin's theory?

Descent with modification from common ancestors; Natural selection acting on variation

What did Wallace independently discover?

Natural selection as the mechanism for evolution, though Darwin had developed the idea earlier

Why do we focus more on Darwin?

He developed the theory more comprehensively and supported it with vast evidence

What did Lyell's "Principles of Geology" teach Darwin?

Uniformitarianism: the Earth is shaped by slow, continuous processes (erosion, volcanoes, earthquakes). Implies a dynamic, gradually changing world

How did Malthus influence Darwin?

His essay on population showed that populations grow faster than food supply → struggle for existence → only favorable variations persist

How did Wallace describe his own realization after reading Malthus?

He concluded that the "fittest" survive — those best adapted (strongest, healthiest, smartest) persist while others die

What are Darwin & Wallace's four key arguments for natural selection?

Overproduction of offspring → struggle for existence; Variation among individuals; Heritability of traits; Cumulative effect: advantageous traits spread over generations

Define natural selection in modern terms.

Heritable variation in fitness (some individuals reproduce more successfully because of heritable traits)

What does "survival of the fitter" mean?

Evolution favors traits that improve reproductive success relative to others, but does not produce perfection

If bacteria in a hospital are exposed to antibiotics, how would Darwin explain the rise of resistance?

Variation in resistance already exists → resistant bacteria survive & reproduce → resistance spreads

What is the raw material for evolutionary change?

Mutations — stable heritable changes in genetic material

What kinds of effects can mutations have?

Neutral: no detectable effect; Small: minor trait changes (e.g., eye color); Large: drastic developmental changes (e.g., homeotic mutations)

Frequency of mutations per gene per generation?

About 1 in 100,000 (rare)

Why do genetic diseases like cystic fibrosis still exist if mutations can be harmful?

Deleterious alleles can persist if recessive, if maintained by drift, or if balanced by heterozygote advantage

Define genetic drift.

Random fluctuations in allele frequencies due to chance events

When is drift strongest?

In small populations

What outcomes can drift cause?

Fixation (allele reaches 100% frequency), or total loss of alleles, regardless of fitness

Why are small endangered populations more vulnerable to harmful mutations spreading?

Drift overwhelms selection, allowing even harmful alleles to persist or fix

What are the three forces of evolution and their roles?

Mutation: introduces variation; Natural selection: filters variation by adaptive value; Genetic drift: randomizes allele frequencies, esp. neutral traits

What do these forces together cause over time?

Long-term genetic change, population divergence, and eventually speciation

Define the biological species concept (BSC).

A species = group of interbreeding populations reproductively isolated from others

What is the role of gene flow in speciation?

Prevents divergence within a species; absence of gene flow allows populations to diverge

What are the steps in speciation?

Barrier forms (geographic, temporal, behavioral, genetic); Populations evolve independently under mutation, selection, and drift; Genetic divergence accumulates until reproductive isolation is complete

Why are island populations often new species?

Geographic isolation cuts off gene flow → independent evolution

How did Darwin's theory replace old views?

Static → dynamic universe; Purposeful design → natural selection as unplanned process; Fixed species → evolving populations

Why is natural selection considered revolutionary?

It showed complex adaptations can arise without a designer, through gradual accumulation of small differences

How does Darwin's theory help us fight antibiotic resistance today?

By predicting that bacteria evolve under selective pressure, we can rotate drugs or use multi-drug strategies to slow resistance