evidence for evolution by natural selection

Evolution

Change in allele frequencies in a population over generations.

Allele frequency

How often a particular allele occurs within a population.

Gene pool

All alleles of all genes within a population.

Natural selection

A mechanism of evolution where heritable traits affect survival and reproductive success.

Fitness

An individual's relative reproductive success.

Heritable variation

Genetic differences between individuals that can be passed to offspring.

Trait

A specific feature or characteristic of an organism.

Phenotype

The observable characteristics of an organism.

Genotype

An organism's genetic makeup.

Adaptation

An inherited characteristic shaped by natural selection that improves fitness.

Speciation

The evolutionary process through which new species arise.

Palaeontology

The scientific study of fossils and ancient life.

Fossil

Preserved remains, impressions or traces of organisms from the past.

Transitional fossil

A fossil showing a mixture of ancestral and derived characteristics.

Geological period

A division of geological time characterised by geological and biological events.

Mass extinction

An event in which a large proportion of Earth's species become extinct.

Vestigial structure

A reduced or modified structure inherited from an ancestor.

Imperfect adaptation

A characteristic that is not perfectly designed because evolution modifies existing structures.

Recurrent laryngeal nerve

A branch of the vagus nerve supplying muscles involved in controlling the larynx.

Plica semilunaris

A small fold of tissue in the inner corner of the human eye, associated with the ancestral third eyelid.

Vagus nerve

A cranial nerve that supplies structures including the larynx through its branches.

Pharyngeal arch

An embryonic structure that contributes to the development of structures in the head and neck.

Biogeography

The scientific study of how organisms are distributed across Earth.

Continental drift

The movement of Earth's continents over geological time.

Endemic

A species naturally restricted to a particular geographical area.

Oceanic island

An island formed away from continental land masses, often geographically isolated.

Divergent evolution

When related lineages accumulate differences over time from a common ancestor.

Convergent evolution

When similar adaptations evolve independently in distantly related lineages.

Carcinisation

The repeated evolution of a crab-like body shape in different crustacean lineages.

Decapod crustaceans

A group of crustaceans including crabs, lobsters and prawns.

Molecular evidence

Evidence for evolution obtained by comparing DNA, RNA or protein sequences.

DNA

The molecule that stores genetic information in most living organisms.

Genetic code

The rules by which nucleotide codons specify amino acids or stop signals.

Synonymous substitution

A DNA change in a coding sequence that does not change the encoded amino acid.

Genetic redundancy

The ability of different codons to encode the same amino acid.

Non-coding DNA

DNA that does not encode proteins; some sequences have regulatory or structural functions.

Neutral Theory

The theory that much molecular variation is selectively neutral and changes through genetic drift.

Neutral mutation

A mutation that has no significant effect on reproductive fitness.

Genetic drift

Random changes in allele frequencies between generations.

Molecular clock

A technique using genetic differences to estimate when evolutionary lineages diverged.

Phylogenetic tree

A branching diagram representing a hypothesis of evolutionary relationships.

Evolutionary lineage

A sequence of populations connected through descent from common ancestors.

Genetic divergence

The accumulation of genetic differences between populations or lineages.

Lactase

An enzyme that breaks down lactose in milk.

Lactose

The sugar naturally found in milk.

Lactase persistence

Continued production of lactase into adulthood.

Pastoralism

The keeping and breeding of livestock for products such as milk and meat.

Gene-culture coevolution

When cultural practices influence genetic evolution and genetic traits influence culture.

Olfactory receptor genes

Genes involved in detecting and recognising smells.

Olfactory receptors

Proteins that detect odour molecules.

Cetaceans

Aquatic mammals including whales, dolphins and porpoises.

Pseudogene

A gene sequence that has lost its original function.

Relaxed selection

A reduction in selective pressure maintaining a particular trait or gene.

Positive selection

Selection that increases the frequency of beneficial genetic variants.

Purifying selection

Selection that removes harmful genetic variants from a population.

Selection pressure

An environmental factor that affects survival or reproductive success.

Phenotypic variation

Differences in observable characteristics between individuals.

Genetic variation

Differences in DNA sequences or alleles between individuals.

Common ancestor

An ancestral organism or population from which two or more lineages descended.

Natural selection in action

Observable differences in survival or reproduction caused by inherited or phenotypic variation.

What did Comte de Buffon suggest about evolution?

Species can vary and change over time.

What did George Cuvier contribute to evolutionary theory?

He demonstrated that species can become extinct.

What did Jean-Baptiste Lamarck propose?

Evolution occurs through the inheritance of acquired characteristics.

What are acquired characteristics?

Traits acquired during an organism's lifetime that Lamarck proposed could be inherited.

What three conditions are required for natural selection?

Heritable variation, variation between individuals and differences in fitness.

Why must characteristics be heritable for natural selection to cause evolution?

They must be passed to offspring so their frequency can change across generations.

Why must traits vary between individuals?

Selection requires differences between individuals to favour some traits over others.

What is fitness in evolutionary biology?

An individual's relative reproductive success.

What does fitness include?

Survival and successful reproduction.

What is evolution?

A change in allele frequencies in a population over generations.

Does all evolution occur through natural selection?

No. Genetic drift, mutation and gene flow can also cause evolution.

What does natural selection act directly on?

Phenotypes rather than genotypes.

How does natural selection affect allele frequencies?

It favours inherited genetic variants associated with greater reproductive success.

What is an adaptation?

An inherited characteristic shaped by natural selection that improves fitness.

Why can natural selection not produce perfect organisms?

It modifies existing variation and is constrained by evolutionary history.

What is speciation?

The evolutionary process through which new species arise.

Why is evolution described as a branching process?

Species diverge from common ancestors rather than progressing along one straight ladder.

What is the main mechanism responsible for adaptations?

Natural selection.

What is a fossil?

Preserved remains, impressions or traces of organisms from the past.

What is palaeontology?

The scientific study of fossils and ancient life.

How do fossils provide evidence for evolution?

They show how organisms and their characteristics change through geological time.

What is a transitional fossil?

A fossil showing a mixture of ancestral and derived characteristics.

Why is the term missing link misleading?

Evolution is branching rather than a straight line with one missing step.

What are geological periods?

Divisions of Earth's history characterised by geological and biological events.

What can cause mass extinctions?

Major environmental changes, climate change and events such as asteroid impacts.

What is a mass extinction?

An event in which a large proportion of Earth's species become extinct.

What were trilobites?

An extinct group of marine arthropods.

When did trilobites disappear?

Approximately 250 million years ago.

For approximately how long did trilobites exist?

About 280 million years, according to the lecture.

How do trilobite fossils demonstrate evolution?

They show changes in physical characteristics across geological time.

Over what relatively short period can trilobite fossils show evolutionary change?

Approximately 3 million years, according to the lecture.

What does the whale fossil record demonstrate?

The evolutionary transition from terrestrial mammals to fully aquatic whales.

What was Pakicetus?

An early whale relative with adaptations associated with life on land.

What was Basilosaurus?

An ancient fully aquatic whale with small vestigial hind limbs.

What do Basilosaurus' small hind limbs demonstrate?

Whales retain remnants of their terrestrial evolutionary ancestry.

How did whale hind limbs change during evolution?

They became greatly reduced as whales adapted to aquatic life.

What is Tiktaalik roseae?

A transitional fossil with fish-like and early tetrapod-like characteristics.

Who discovered Tiktaalik?

Neil Shubin and colleagues.

Where was Tiktaalik discovered?

Ellesmere Island in the Canadian Arctic.