Evolution
The origins and diversification of living systems.
32 problemsBiology
Living systems, their origins, and their mechanisms.
Explore Biology
Molecular and cell biology
Cells, genes, and the mechanisms that organize living systems.
62 problemsEcology
Interactions among organisms and their environments.
21 problemsDisease mechanisms
The biological processes that cause or sustain disease.
7 problemsOrigins of life
How nonliving chemistry could give rise to living systems.
4 problemsPlant biology
Plant development, responses to light and gravity, reproduction and evolutionary history.
11 problemsCollections
Browse collectionsOrigins and complexity
From the first living systems to complex cells and multicellular organisms, explore several transitions in life’s history.
10 problemsGenes and development
How do genomes and regulatory systems shape traits, reliable development, and repair?
32 problemsInside cells
Molecular traffic, cell machinery, patterned shells and signals between cells.
14 problemsA few problems to explore
88 totalOrigin of life
Before there were cells, there were molecules. How did chemical systems begin passing useful abilities to descendants and sustaining their own reproduction?
Biological aging
Cells change, tissues lose resilience and organs age at different rates. Which changes drive the others, and how do they become a whole-body process?
Eukaryogenesis
Complex cells with nuclei descended from simpler ancestors. How did their internal compartments, mitochondria, and distinctive cellular organization come together?
Functions of sleep
Sleep is essential, but why do its benefits require a state in which an animal becomes less responsive to its surroundings?
Evolution of multicellularity
Cells have repeatedly evolved into organisms that live and reproduce together. What turns a group of cells into a coherent evolutionary individual?
Sex chromosome evolution
Some lineages keep the same sex chromosomes for vast spans of time; others replace them repeatedly. Why do their evolutionary paths differ so much?