Organ (biology)

In biology, an organ is a group of tissues that work together in an organism. They specialise in particular vital functions. They create an organ system which, as a whole, is an organism.

These are examples of organs:

Classification

Organelles > Cells > Tissues > Organs > Organ systems > Organism

v t e Evolutionary biology
Evolution	Abiogenesis Adaptation Adaptive radiation Cladistics Coevolution Mutualism Common descent Convergence Divergence Earliest known life forms Evolutionary arms race Exaptation Extinction Event Homology Last universal common ancestor Macroevolution Microevolution Origin of life Panspermia Parallel evolution Signalling theory Handicap principle Speciation Species Species complex Species problem Altruism Cheating Reciprocal Baldwin effect Evidence of evolution Evolutionary pressure Mismatch Non-adaptive radiation Taxonomy Unit of selection Gene-centered view of evolution
Population genetics	Artificial selection Biodiversity Evolutionarily stable strategy Fisher's principle Fitness Inclusive Gene flow Genetic drift Kin selection Parental investment Parent–offspring conflict Mutation Population Natural selection Sexual dimorphism Sexual selection Mate choice Social selection Trivers–Willard hypothesis Variation
Development	Canalisation Evolutionary developmental biology Genetic assimilation Inversion Modularity Phenotypic plasticity
Of taxa	Birds origin Dinosaurs Fish Mammals canids wolves dogs hyenas dolphins and whales horses primates humans lemurs cats Kangaroos sea cows Bacteria Brachiopods Molluscs Cephalopods Fungi History of life Insects butterflies Plants pollinator-mediated Reptiles Spiders Tetrapods Viruses
Of organs	Cell DNA Flagella Eukaryotes symbiogenesis chromosome endomembrane system mitochondria nucleus plastids In animals eye hair auditory ossicle nervous system brain
Of processes	Aging Death^{[broken anchor]} Programmed cell death Avian flight Biological complexity Cooperation Color vision in primates Emotion Empathy Ethics Eusociality Immune system Metabolism Monogamy Morality Mosaic evolution Multicellularity Sexual reproduction Gamete differentiation/sexes Life cycles/nuclear phases Mating types Meiosis Sex-determination Snake venom
Tempo and modes	Gradualism/Punctuated equilibrium/Saltationism Micromutation/Macromutation Uniformitarianism/Catastrophism
Speciation	Allopatric Anagenesis Catagenesis Cladogenesis Cospeciation Ecological Hybrid Non-ecological Parapatric Peripatric Reinforcement Sympatric
History	Renaissance and Enlightenment Transmutation of species David Hume Dialogues Concerning Natural Religion Charles Darwin On the Origin of Species History of paleontology Transitional fossil Blending inheritance Mendelian inheritance The eclipse of Darwinism Neo-Darwinism Modern synthesis History of molecular evolution Extended evolutionary synthesis
Philosophy	Darwinism Alternatives Catastrophism Lamarckism Theistic Orthogenesis Mutationism Saltationism Structuralism Spandrel Vitalism Teleology in biology
Related	Ecological genetics Evolutionary medicine Group selection Cultural evolution Cultural group selection Dual inheritance theory Molecular evolution Astrobiology Phylogenetics Tree Systematics Hologenome theory of evolution Missing heritability problem Polymorphism Protocell Transgenerational epigenetic inheritance