Unit 3 - Lecture 2 - Evidence of Evolution

What are common real-world examples of natural selection in action?

Drug resistance in microorganisms, pesticide resistance, and host-switching in insects

Why do microorganisms and insects evolve so quickly?

Strong selective pressures and short generation times.

How does warfarin kill rats?

Warfarin interferes with synthesis of blood-clotting factors → bleeding → death.

What gene mutation gives rats resistance to warfarin?

Mutations in the VKORC1 gene

What happens to warfarin-resistant rats when warfarin is not being used?

Resistance alleles can be disadvantageous in poison-free environments. (Natural selection is time-and-place dependent.)

Why is the warfarin example important?

It shows that natural selection is an editing mechanism—it works on existing variation

How did soapberry bugs show natural selection?

A new flatter fruit became common → shorter beaks became favoured → population’s average beak length decreased.

What type of selection does the soapberry bug example illustrate?

Directional selection (towards shorter beaks).

What are the 3 major sources of evidence for descent with modification?

Homology, biogeography, and the fossil record

What is homology?

Similarity due to common ancestry

What are anatomical homologies?

Similar structures across species caused by shared ancestry (e.g., mammalian forelimbs)

What are vestigial structures? Give an example

Reduced structures with little/no current function, derived from ancestors.

Example: Hind-limb bones in whales/snakes.

What are molecular homologies?

Shared biochemical traits due to common ancestry (e.g., the universal genetic code).

What are pseudogenes?

nonfunctional DNA sequences that are molecular vestigial features

What pattern do homologies typically show across groups of organisms?

a nested distribution that fits a branching tree-of-life

What is an analogous structure?

Structures with similar function but NOT from common ancestry—due to convergent evolution.

What is convergent evolution?

Different lineages independently evolving similar adaptations due to similar environments.

What is biogeography?

The geographic distribution of species.

What does it mean if a taxon is endemic?

It is restricted to a specific location.

How does biogeography support evolution?

Endemic groups often descend from a common ancestor that lived in that region.

What is an adaptive radiation?

Rapid evolution of many species from a common ancestor in underexploited habitats.

Why are island chains hotspots for adaptive radiations?

They offer new habitats, low competition, and isolation → rapid diversification.

Give an example of an adaptive radiation in plants

Hawaiian Silversword Alliance (~50 species evolved from one ancestor in ~5 MYA)

what are fossils?

Preserved remains or traces of past life (mineralized remains, petrified material, casts, footprints)

Why is the fossil record important for evolution?

It gives a direct view of past life and shows transitional forms

What does descent with modification predict about fossil sequences?

Transitional forms should appear between major groups

What is the “order of appearance” principle in fossils?

Ancestor groups appear earlier in the fossil record than their descendants

Describe the fossil evidence for whale evolution.

Many transitional forms link land mammals (like Pakicetus) to modern whales (fully aquatic)

When did the first aquatic whale-like fossils appear?

~50 million years ago

When did the first eutherian land mammals appear?

~80 million years ago. (Consistent with whales evolving later.)

List the major lines of evidence supporting evolution

Natural selection in action, homology, analogy vs convergent evolution, biogeography, adaptive radiations, and the fossil record (transitional forms + order of appearance).

What is the overall conclusion of these evidence lines?

All support descent with modification and a branching tree-of-life