Evolution

32 problems

Eukaryogenesis

Complex cells with nuclei descended from simpler ancestors. How did their internal compartments, mitochondria, and distinctive cellular organization come together?

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?

Origin of the genetic code

Cells translate genetic sequences into proteins. How did a code and the machinery that reads it arise together?

Origin of viruses

Viruses have remarkably different genomes and structures. Did their major lineages emerge independently, and from what ancestors?

Flowering plant origins

Fossils and DNA offer different timelines for the earliest living flowering-plant lineages. Why do their estimated beginnings still disagree?

Mast seeding

Some plants produce huge seed crops together, then little for years. How do weather cues and stored resources set that rhythm?

Maintenance of sexual reproduction

Sexual reproduction can be costly compared with reproduction without a partner. Why does it persist so widely?

Genome size evolution

Closely related organisms can carry very different amounts of DNA. What determines how genomes expand or shrink?

Bacterial speciation

Bacteria exchange DNA across lineages. How do distinct evolutionary populations form and remain separate?

Cambrian explosion

Animal body plans diversified rapidly around the Ediacaran–Cambrian transition. What combination of changes drove that radiation?

Rangeomorph nutrition

Rangeomorphs were branching Ediacaran organisms. How did they obtain nutrients in the deep-sea settings where some lived?

Evolution of menopause

Some mammals live long after reproduction ends. Which evolutionary conditions make that unusual life history favorable?

Mitochondrial DNA bottleneck

A mother’s mix of mitochondrial DNA variants can change sharply between generations. What physical sampling process drives that change?

Mammalian replication origins

Mammalian DNA replication can begin at many licensed sites. What determines which sites actually start copying in a given cell?

Mitochondrial gene retention

Mitochondria keep some genes while many others reside in the nucleus. Why do different lineages retain different sets?

Meiotic homologue recognition

During egg formation in fruit flies, matching chromosomes must find one another. How do repeated DNA sequences help them recognize a match?

Insect photoperiodic timing

Insects use day length to prepare for seasonal dormancy. How do daily clock signals become a seasonal decision?

Polyploid establishment

A plant with extra chromosome sets may have few compatible mates. Which conditions let a new polyploid population persist?

Segregation Distorter mechanism

A selfish chromosome in fruit flies disables competing sperm. How does its genetic machinery cause that selective failure?

Speciation with gene flow

New species can diverge while exchanging genes. How do reproductive barriers combine to sustain separation?

Bergmann’s rule

Many birds are larger in colder places, but the pattern varies. Which inherited and developmental mechanisms create these geographic size differences?

Great Ordovician Biodiversification Event

Marine diversity expanded dramatically around the Ordovician. How did ecological change, nutrient cycling and climate interact to produce that diversification?

Oxytricha genome rearrangement

Oxytricha rebuilds its working genome from scrambled DNA segments. How do RNA instructions become correctly ordered DNA joins?