Unit 8
Evolution.
How populations change over generations: natural selection, antibiotic resistance, fossils, and sorting life by ancestry.
Before this unit
The unit, lesson by lesson
Lessons
5 lessons · 28 practice questions · about 2 hours
Natural selection
Moths on tree bark: variation already in the population, birds that select, adaptation over generations, and why without selection almost nothing changes.
Antibiotic resistance
Natural selection within days: a few resistant mutants among a billion bacteria, a selection window that picks them out, why you finish the course, and why a low dose is dangerous.
The fossil record
Why most living things never become fossils, which conditions keep even the soft parts, and how rock layers and dated ash beds tell how old a fossil is.
Classifying life
The ranks from domain to species, the difference between sorting by looks and sorting by ancestry, shared ancestors on the tree of life, and why a whale is close to a hippo.
The clock of life
All 4.5 billion years of the Earth squeezed into one day and one year: microbes alone for most of the day, animals arriving in the evening, dinosaurs in December, and our species in the last seconds.