Glossary

Clearly defined terms are vital to communicating concepts in science. Alphabetically listed, these terms play four crucial roles in science –

Clarity and Precision: Definitions provide clarity by precisely delineating the meaning of terms. Acting as a compass, a well-crafted definition helps to navigate the intellectual landscape.

Foundation for Knowledge: Scientific progress relies on shared understanding. Clear definitions establish a common language, allowing for effective communication. Without definitions, discussions become muddled, hindering progress.

Testable Explanations: Science aims to build knowledge through testable explanations and predictions. Definitions underpin these explanations. For instance, defining “gravity” allows us to formulate hypotheses and experiments with this force.

Boundary of Science: Definitions also delineate what falls within the scope of science. Anything supernatural or beyond the natural world lies outside this boundary. By defining these limits, science maintains its rigor and focus.

In summary, definitions are the bedrock upon which scientific inquiry rests, providing clarity, precision, and a shared framework for understanding the world. Understanding the terms is essential for assessing, evaluating, defining, and communicating the concepts of evolution. Extended coverage is available by clicking on the linked words.

Adaptation: Changes within an organism to adjust to a niche or survive in an environment.

Adaptive Evolution: A change or adjustment in structure or habits by which a species adjusts to its environment through natural selective changes in allele frequencies over time within a population, also known as microevolution.

Adaptive Phenotypic Plasticity: Degree to which an organism’s phenotype changes depending upon its current or past environment. Two organisms with the same genotype (e.g., identical twins) may have different phenotypes (e.g., one may be taller or heavier) if raised in different environments; those differences represent phenotypic plasticity.

Adaptive Radiation: The diversification of species to live in a specific environmental niche.

Age of Enlightenment: An intellectual and philosophical movement that dominated Europe in the 17th and 18th centuries with global influences and effects.

Alleles: One of two, or more, forms of a given gene variant.

Allopatric Speciation: A mode of speciation when some members of an original species become geographically separated. Theoretical term.

Anagenesis: Consecutive ladder-like steps in a single evolutionary lineage where one ancestral species evolves directly into a descendant species. Theoretical term.

Analogous: Similar traits or functions arriving from similar environmental exposures. Theoretical term.

Anatomy: As a subdivision of morphology, studies biological structures macroscopically or microscopically. Macroscopic anatomy, or gross anatomy, examines structures without instrumentation, also known as superficial anatomy. Microscopic anatomy uses optical instruments to study tissue structures.

Ancestral Lineage: A temporal series of populations, organisms, cells, or genes connected by a continuous line of descent from ancestor to descendant.

Animalia: The basic groups of living things.

Anthropocentric: Centering on humans and considering all other things in relation to humans.

Anthropology: The scientific study of humanity, concerned with human behavior, human biology, cultures, societies, and linguistics in both the present and past, including past human species.

Appendage: Any limb that extends from the body. Arms and legs, for example, are appendages.

Apomorphy: A trait unique to a species or group.

Archaea: One of the three domains of life composed of single-celled organisms that lack cell nuclei, also known as prokaryotes. Bacteria and Eukaryota are the other two domains. Theoretical term.

Artificial Selection: Characteristics selected by humans.

Astrobiology: The branch of science that investigates the possibility of life beyond Earth. Theoretical term.

Atavism: Modification of a biological structure whereby an ancestral genetic trait reappears after having been lost in previous generations. Theoretical term.

Atomic Clock: Measure the precise length of a second, based the time it takes a caesium-133 atom to oscillate between the two hyperfine levels.

Bacteria: Single-celled organisms’ domain lacks a few organelles and a true nucleus, also known as prokaryotes. Archaea and Eukaryota are the other two domains.

Base: A nucleic acid building block acting as a letter in the DNA and RNA genetic information code. The four bases of DNA are Adenine (A), Thymine (T) [Uracil in RNA], Guanine (G), and Cytosine (C).

Bayesian Inference: A method of statistical inference in which Bayes’ theorem is used to update the probability for a hypothesis as more evidence or information becomes available; closely related to subjective probability. .

Bayesian Probability: An interpretation of the concept of probability, in which, instead of frequency or propensity of some phenomenon, probability is interpreted as reasonable expectation.

Big Bang: The event that marked the beginning of the universe.

Bilateral Symmetry: A condition in which the right and left sides of an item (e.g., a shape or an animal) are mirror images of one another.

Biocenoses: An association of different organisms forming a closely integrated community.

Biochemistry: The study of the chemical substances and vital processes occurring in living organisms. .

Biodiversity: Variety of organisms with genetic differences in an ecosystem.

Biodiversity Hotspot: A region that provides a home to an unusually high density of different species.

Biogenic Elements: Chemical elements present in organisms required for biological molecular processes. Biogenic elements include, but are not limited to, carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorous.

Biogenetic Law: The theory of recapitulation, often expressed using Ernst Haeckel’s phrase, “ontogeny recapitulates phylogeny.” Theoretical term.

Biogeochemical: Relating to or denoting the cycle in which chemical elements and simple substances are transferred between living systems and the environment.

Biogeography: Study of species distribution across the Earth.

Biological Evolution: An inferred explanation accounting for the natural origin of all living things theoretically over time through “slight, successive” changes.

Biological Nomenclature Organizations: Organizations dedicated to naming life forms. (Click for extended coverage.)

Biological Organization: A hierarchy of complex biological structures and systems that define life using a reductionistic approach. Theoretical term.

Biological Species Concept: A species is a population of interbreeding natural populations reproductively isolated from other populations.

Biology: Study of living organisms scientifically.

Biomass: Total mass of all living organisms in a particular area.

Binomial Name: A binomial name of a species is composed of the generic (Genus) name and the specific name of the species, a two-part name. Synonyms: binomen, scientific name, Latin name.

Binomen: Synonymous with binomial name.

Biosphere: The worldwide sum of all ecosystems, integrating all living beings and their relationships.

Biostratigraphy: A way of determining the relative ages of different fossil species by looking at how layers, or strata, of sedimentary rocks, are positioned relative to one another.

Bleeding Inheritance: The progeny inherits any characteristic as the average of the parents’ values of that characteristic. Theoretical term.

Bottleneck: Reduced inferred evolution potential. Theoretical term.

Brood: A offspring collective, also known as a progeny.

Burgess Shale: Rich deposit of fossils from the Cambrian Period located in western Canada.

Cambrian Explosion/Period: Burst of new life at the start of the Paleozoic Era. Theoretical term.

Carbon Dating: A method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.

Catastrophism: The sudden plate tectonic and flooding event reported by Moses in Genesis chapter 8.

Central Dogma of Molecular Biology: Deoxyribonucleic acid (DNA) is the absolute governor of life and inheritance. The driving mechanism of inferred evolution involves an accumulation of random DNA changes (mutations) transmitted into RNA that produces the new proteins required for a speciation event. Theoretical term.

Chirality: Non-superimposable mirror images.

Chromosomal Fission: A process leading to an increase in the number of chromosomes.

Chromosomal Fusion: A process leading to a decrease in the number of chromosomes.

Chromosome: A cellular structure made of DNA and proteins that contain all or part of an organism’s heritable, genetic information. Humans have 23 pairs of chromosomes.

Chromista: A biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles (plastids).

Clade/Clades: A group of organisms that are classified in the same taxon and share a most common recent ancestor; also known as a monophylogeny. Theoretical term.

Cladistics: Method of classifying species in groups based on ancestral relationships. Theoretical term.

Cladogenesis: Successive branching events produce many species that are closely related and therefore look similar to each other, but represent inferred evolutionary “cousins” rather than ancestors and descendants. Theoretical term.

Cladogram: Diagram of inferred evolutionary relationships between different organisms. By comparison, a phylogenetic tree shows the relationship between different organisms with respect to inferred evolutionary time and the amount of change with time. Theoretical term.

Class: A term denoting the level of classification or taxonomic rank below phylum and above order. Theoretical term.

Classical Genetics: Discovered by Gregor Mendel, classical genetics is composed of the Law of Segregation and Independent Assortment Law, also known as Mendel’s Laws of Inheritance:

Codon: A three-base unit of DNA that specifies an amino acid or the end of a protein.

Coevolution: A process in which two interacting species evolve together, with each species influencing the other’s inferred evolution. Theoretical term.

Commensalism: An association between two organisms in which one benefits and the other derives neither benefit nor harm.

Common Ancestor: Descendant’s shared ancestor of Earth’s biosphere. Theoretical term.

Common Descent: The concept of the common ancestor process. Theoretical term.

Comparative Anatomy: Study of the similarities and differences in the structures of different species

Comparative Embryology: Study of the similarities and differences in the embryos of different species.

Concept: An abstract idea that can be generalized from specific instances or occurrences.

Constraint: Limited evolution potential. Theoretical term.

Continuum: A continuous sequence in which adjacent elements are not perceptibly different, although the extremes are quite distinct.

Convergent Evolution: The development of homologous features in different species emerging from similar environments. Theoretical term.

Correlation Coefficient: A numerical measure of some correlation, meaning a statistical relationship between two variables. Theoretical term.

Coprolite: Fossilized dung.

Correlated Growth: A phrase used in the Origin of Species to describe “variation” but never defined by Darwin. Theoretical term.

Cosmic Rays: Rays consist mostly of protons or atomic nuclei moving through space at close to the speed of light not derived from the Sun, but exploding stars outside our solar system.

Cosmic Time: The time that has elapsed since the Big Bang, the event that is believed to have marked the beginning of the universe.

Cosmogenetic Dating: Dating technique using the amount of cosmic rays that hit the surface of the Earth.

Cosmology: The study of the origin and development of the universe.

Cospeciation: A term to describe how one species can dictate the speciation of another species; a term applicable to host-parasite relationships. Theoretical term.

Creation: The action or process of bringing something new into existence.

Creationism: A view to explain the origin of the universe and life compatible with the Genesis account.

Cross Breeding: Breeding between two different breeds, varieties, or populations of the same species.

Data Matrix: In phylogenetics, a data set consisting of a list of taxa and a set of those taxa’s attributes (called characters and character states). Data matrices are used to build evolutionary trees.

Darwin, Charles: Author of the Origin of Species, originator of the theory of natural selection.

Darwin Skeptics: Scientist and philosopher’s assessments of Darwin’s theory of evolution (for extended coverage, clink on the term).

Darwinian Evolution: Differential reproduction of genotypes, based on the feedback from the environment transmitted through the phenotype. Theoretical term.

Darwinism: An evolution concept to describe the origin of life “by means” of natural selection, also known as Darwinian evolution. Theoretical term.

Darwin: The darwin(d) is a a unit of measurement used to standardize evolutionary rates originally defined as an e-fold (about 2.718) change in a trait over one million years.

Darwin’s Dilemma: The geologically sudden appearance of dozens of major complex animal types in the fossil record without any trace of the gradual transitional steps.

Darwin’s Species Problem: Species is a fundamental concept in modern biology, forming the building blocks of Earth’s vast and diverse biosphere. “Darwin’s species problem” begins with the definition of species.

Dating Fossils: The estimate of the age of a fossil typically through biostratigraphy and radiometric dating (for extended coverage, clink on the term).

Deductive Reasoning: A process of reasoning that begins with general ideas to develop a specific conclusion. (Click to differentiate deductive reasoning from inductive reasoning)

Definition: A statement of the meaning of a word or a symbol.

Degradation: The lowering of a stream bed or floodplain through erosional processes.

Deleterious allele: A version of a gene that, on average, decreases the fitness of the organism carrying it.

Derived Character State: The character state present in a lineage immediately after a character state change. Theoretical term.

Descent: Passing down traits.

Development: Change in an organism over the course of its lifetime; the processes through which a zygote becomes an adult organism

Differentiation: The action or process of differentiating.

Dimorphic: Representing two distinct forms.

Directional Selection: A type of natural selection favoring an extreme characteristic resulting in a shift of the phenotypic distribution toward that extreme. Theoretical term.

Disruptive Selection: The type of natural selection favors both extremes and selects against the average characteristics, resulting in two overlapping phenotypes at each end of the distribution. Theoretical term.

Determinism: The philosophical view that previously existing causes entirely determine all events.

Diversifying Selection: Natural selection favors different genotypes in different subenvironments. Theoretical term.

DNA (deoxyribonucleic acid): Double-stranded nucleic acid molecule, the building blocks of genes and chromosomes.

DNA Replication: Process of copying DNA before cell division domain.

Domain: A term to denote life’s highest taxonomic rank of organisms. Theoretical term.

Ecological Succession: Changes through time in the numbers and types of species that make up the community of an ecosystem.

Ecological Adaptation: Any physiological, behavioral, or morphological attribute of an organism that enables it to survive and reproduce in its respective habitat.

Ecological Speciation: Speciation resulting from different environments or resources. Theoretical term.

Ecology: Study of how living things interact with each other and with their environment.

Ecosystem: Biological community of interacting organisms and their physical environment.

Embryo: Early stage of development of a multicellular organism.

Embryology: Study of the earliest stages of development of an unborn organism.

Empirical Evidence: information acquired by observation or experimentation.

Empirical Research: Applying the principles of science to investigate a real-world phenomenon to gain insights into varying biological characteristics.

Encode: To convert (something, such as a body of information) from one system of communication into another

Endemic: Constantly maintained at a baseline level in a geographic area without external inputs.

Endosymbiotic Theory: Eukaryotic organelles (e.g., mitochondria) originated from invading ancient prokaryotes theory. Theoretical term.

Entropy: A measurable physical property commonly associated with a state of disorder, randomness, or uncertainty; a concept developed from classical thermodynamics.

Epigenetic: Non-genetic biological factors.

Epigenetic Inheritance: Inherited non-genetic biological factors.

Equivocal: Open to more than one interpretation; ambiguous.

Eukaryota: One of the three domains of life whose cells have a nucleus enclosed within a nuclear envelope. Archaea and Bacteria are the other two domains. Theoretical term.

Eukaryote: A unicellular organism with an enclosed nucleus.

Eusociality: Advanced level of social organization, in which a single female or caste produces the offspring and nonreproductive individuals cooperate in caring for the young.

Evidence: The available body of facts or information indicating whether a belief or proposition is valid.

Evolution: Inferred changes in characteristics over time. Biological evolution is divided into the subcategories of macroevolution and microevolution.

Evolutionary Development Biology (Evo-Devo): A field of biological research that compares the developmental processes of different organisms to infer the ancestral relationships between them and how developmental processes evolved. Theoretical term.

Evolutionary Rate: The speed at which some inferred evolutionary process occurs. Theoretical term.

Evolutionary Tree/Phylogenetic Tree: A representation of the hypothesized evolutionary relationships among a group of organisms. Theoretical term.

Evolvability: The capacity for adaptive evolution.

Exaptation: A feature that performs a function but that did not arise through natural selection for its current use. Theoretical term.

Exogenous: Relating to or developing from external factors.

Exon: A region of DNA that is transcribed into RNA. Exons include all the protein-coding regions of a genome, plus the regions that code for rRNA and tRNA.

Experimental Research: Experimentally tests a hypothesis for cause-and-effect relationships by systematically manipulating one or more independent variables and measuring their effect on one or more dependent variables.

Extant: Not extinct, currently living.

Extended Evolutionary Synthesis: A set of theoretical concepts argued to be more comprehensive than the earlier modern synthesis of inferred evolutionary biology between 1918 and 1942.

Extension: The capacity to recruit additional variables that can be utilized to sustain the system and the ability to exclude variables that could destabilize the system.

Extinction: The complete loss of a species with no remaining members alive on Earth.

Extremophile: An organism that lives in an environment of extreme temperature, pressure, acidity, alkalinity, or other physical conditions normally not tolerated by other forms of life.

Fact: An occurrence in the real world. The usual test for a statement of fact is verifiability—whether it corresponds to experience. Verified scientific facts are repeatable observations and measurements.

Facultative Trait: A trait in which the phenotypic expression of the genotype has been shaped by natural selection such that environmental variation triggers the production of different adaptive phenotypes well-suited to that environment — i.e., a trait with adaptive phenotypic plasticity. Theoretical term.

Falsification: A testing procedure to assess the validity of a theory by withstanding rigorous attempts to falsify the theory; also known as placebo testing.

Falsifiability: Property of a theory, hypothesis, or statement that can be logically contradicted by an empirical test or a fact.

A theory or hypothesis is falsifiable (or refutable) if it can be logically contradicted by an empirical test to ensure the theory is predictive and testable. Valid scientific theories generate testable predictions.

Family: One of the eight major hierarchical taxonomic ranks in Linnaean taxonomy, it is classified between order and genus. Theoretical term.

Family Tree: A branching pattern retracing an organism’s inferred evolutionary history; also known as a phylogenetic tree, with common ancestors appearing at the base and nodes of the tree.

Fauna: All of the animal life present in a particular region or time.

Fitness: An organism’s ability to survive and reproduce in a particular environment.

Fossil: Preserved life form that once lived on Earth.

Fossil Preservation: The process of preserving life forms that once lived on Earth.

Fossil Record: The collective remains or imprints of preserved forms of life that once lived on Earth.

Fossilization: The process of becoming a fossil.

Fossiliferous: Fossil containing object.

Frequency Gaps: Dynamical variables split among distinct levels of organization separated by sufficiently wide frequency gaps.

Fungi: Any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms.

Gene: The unit of heredity. Generally, it means a region of DNA with a particular phenotypic effect.

Gene Cloning: Process of isolating and making copies of a gene.

Gene Conversion: A mechanism of mutation associated with recombination in which a cell’s DNA repair systems “convert” the sequence on a section of one chromosome to a sequence that is found on the homologous chromosome.

Gene Expression: Use of a gene to make a protein.

Gene Flow: Transfer of genetic material from one population to another.

Gene Frequency: Proportion of genes/alleles in a population that are of a particular type. Also called allele frequency.

Gene Pool: All of the genes in a population.

Gene Theory: Inheritable genes control the characteristics of living things theory.

Gene: Unit of DNA on a chromosome encoded with the instructions for a single protein.

General Relativity: The geometric theory of gravitation.

Generations: The average period, generally considered to be about thirty years, includes newborns becoming adults and delivering newborns.

Genetic Drift: Random change in allele frequencies that occurs in a small population.

Genetic Recombination: The process of exchanging genetic material between different organisms, also known as genetic recombination. Theoretical term.

Genetic Shuffling: The process of exchanging genetic material between different organisms, also known as genetic reshuffling. Theoretical term.

Genetic Trait: Characteristic encoded by DNA.

Genetic Transfer: Method of increasing genetic variation in prokaryotes that involves cells “grabbing” stray pieces of DNA from their environment or exchanging DNA directly with other cells.

Genetic Variation: Differences in DNA among individuals or the differences between populations.

Genetics: Study of genes, genetic variation, and heredity in organisms.

Geobiology: Applies the principles and methods of biology, geology, and soil science to study interactions between living organisms and non-living elements of Earth.

Genome: DNA or RNA information storage unit of an organism.

Genomics: Genomics is the study of all of a person’s genes (the genome), including interactions of those genes with each other and with the person’s environment.

Geochronology: The study of Earth’s history from the perspective of time in rocks, fossils, and sediments.

Genotype: An organism is its complete set of genetic material.

Genus (Kind): The level of classification or taxonomic rank below family and above species.

Geographic Isolation: Separation of two populations by a physical barrier.

Geological Age: A system of chronological dating that classifies geological strata (stratigraphy) in time.

Geographic Speciation: Speciation resulting from spatial separation. Theoretical term.

Geologic Column: A columnar diagram of rock formations arranged, indicating their relations to geologic time. Theoretical term.

Geologic Time Scale: Timeline of Earth based on a synthesis of geological and paleontological observations.

Germ Line Mutation: Mutation that occurs in reproductive cells and ends up being carried by gametes (e.g., eggs and sperm).

Germinal Vesicle: The fluid-filled nucleus of an oocyte toward the end of the prophase of its meiotic division.

Ghost Lineages: Hypothesized ancestor in a species lineage that has left no fossil evidence, but inferred to exist or have existed because of gaps in the fossil record or genomic evidence. Theoretical term.

Gradualism: Changes developing over long periods.

Gravity: The mutual attraction between all things that have mass, determines the motion of planets, stars, galaxies, and light. .

Habitat: Physical environment in which a species lives.

Habitat Loss: Destruction or disruption of Earth’s natural habitats.

Habitable Zone: The region surrounding a star in which planets with liquid water on their surfaces may exist.

Haploid: Individual or cell that carries one set of its chromosomes. Human eggs and sperm are haploid. They usually carry one copy of each of our 22 regular chromosomes and either an X or a Y sex chromosome.

Herbivore: An organism that eats almost entirely plants (herb = plant, vorare = to swallow up).

Heredity: A property of systems in which intrinsic characteristics are passed from parent(s) to offspring.

Heritable Characteristics: A measure of how well differences in people’s genes account for differences in their traits, e.g., height, eye color, intelligence, and disorders like schizophrenia and autism spectrum disorder.

Heterochrony: An inferred evolutionary change in the timing of a developmental event. Theoretical term.

Heterozygote: An individual carrying two different gene versions for a particular gene.

Hierarchical Organization: A structure where all the entities except the topmost are subordinate to another entity. Theoretical term.

Hierarchical Scales: Multiple dynamical variables that change on different temporal scales.

Historical Science: Data is provided primarily from past events and for which there is usually no direct experimental data. Paleontology, archaeology, geology, astronomy, cosmology, philology, and history are historical sciences.

HMS Beagle: British naval vessel aboard which Charles Darwin served as naturalist on a voyage to South America and around the world (1831–36).

Homeobox Gene: Clusters of regulatory genes spatially and temporally used during embryological development.

Hominid: Humans and their extinct relatives. Some scientists use the term hominid to refer to a larger group: humans, other great apes (gorillas, chimpanzees, bonobos, and orangutans), and their extinct relatives. Theoretical term.

Hominin: Clade that includes all humans, human ancestors, and human relatives. Theoretical term.

Homologous Structures: Similarities of body parts on different species from a shared ancestor. Theoretical term.

Homology: The state of having the same or similar relation, relative position, or structure.

Homoplasious: Similar but not because of inheritance from a common ancestor. Homoplasious characters may be explained by inferred convergent evolution in two different organisms or character reversals. Theoretical term.

Horizontal Gene Transfer: A process that results in the transfer of genetic material between members of different species.

Host: Organism that serves as a habitat for another organism.

Host-Switching: Change of the host specificity of a parasite or pathogen.

Hox Gene: A gene that regulates the development and organization of the major body units.

Hybrid: Offspring of two different types of parents.

Hydrothermal Vents: Extremely high-temperature water flowing into the ocean from the Earth’s Core.

Hypothesis: A tentative conjecture explaining an observation, phenomenon, or scientific problem that can be tested by further observation, investigation and/or experimentation.

Inbreeding: A pattern of mating in which mates are more closely related than two individuals selected at random from the population.

Incipient Species: A group of organisms that is about to become a separate species from other, related individuals. Theoretical term.

Independent Assortment Law: Different genes and their alleles are inherited independently, one of the two fundamental aspects of Mendel’s classical genetics theory.

Independent Variable: The independent variable is “independent” because its variation does not depend on the variation of another variable in the experiment/research project. The independent variable is controlled or changed only by the researcher.

Inductive Reasoning: A process of reasoning that begins with specific known factors to develop general rules or hypotheses. (Click to differentiate deductive reasoning from inductive reasoning)

Information-Flow: Slower-changing levels absorb information from faster-changing levels during learning and pass information down to the faster levels.

Information-Processing Units (IPUs): Changing the form of information to another form of information, e.g., changing from genome to phenotype.

Inheritance of Acquired Characteristics: Inheritance of traits that an organism develops in its lifetime.

Intelligent Design: View that the universe and life are the work of an intelligent designer.

Interbreeding: Breeding between different species.

Intermediate Forms: Organisms that are intermediate between an ancestor and descendants; also referred to as transitional forms. Theoretical term.

International Atomic Time (IT1): Time scale calculated by a network of atomic clocks.

Invertebrate: Animals that neither possess nor develop a vertebral column (commonly known as a backbone or spine) derived from the notochord.

Kind (Genus): The level of classification or taxonomic rank below family and above species.

Kingdom: The second highest taxonomic rank, just below domain. Theoretical term.

Last Universal Common Ancestor (LUCA): The original shared form of life for related species; also called the last universal ancestor (LUA), or the most recent common ancestor (MRCA). Theoretical term.

Latin Name: Synonymous with species’ binomial name.

Law of Correlation: A phrase used in the Origin of Species to describe “variation,” but the phrase was never defined by Darwin. Theoretical term.

Law of Nature: Stated regularity in the relations or order of phenomena in the world.

Law of Segregation: A diploid individual possesses a pair of alleles for any particular trait. Each parent passes one of these randomly to its offspring, one of the two fundamental aspects of Mendel’s classical genetics theory. Theoretical term.

Laws: Unchanging principles.

Laws of Nature (Scientific Laws, Scientifically Valid Theory): Empirically testable and falsifiable statements and/or equations that predictably describe unchanging principles in nature.

Life History: An organism’s history of changes.

Lineage: A continuous line of descent; a series of organisms, populations, cells, or genes connected by ancestor/descendent relationships.

Lineage Splitting: An event in which a species gives rise to two or more descendent lineages. Every node on a phylogeny is a lineage-splitting event. Theoretical term.

Linnaean System of Classification: Standard system of classification in which every organism is assigned a kingdom, phylum, class, order, family, genus, and species. This system groups organisms into smaller and smaller groups (like a series of boxes within boxes, called a nested hierarchy).

Locus: Gene location in the DNA structure.

Logic: A way of thinking about or understanding something using a reasoning process; the study of the laws of thought using inferences or arguments.

Loss of Function: The loss of function of time-dependent variables.

Lowest Common Ancestor: An ancestor shared between related species closest to the tree’s root. Theoretical term.

Macroevolution: Inferred process generating the development of distinct reproductive population units from preexisting forms through successive generations driven by natural selection. Theoretical term.

Major Transition in Evolution (MTEs): Inferred biological transition leading to the emergence of a distinct new species. Theoretical term.

Mammal: A group of vertebrate animals constituting characterized by mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or hair, and three middle ear bones.

Mass Extinction: Event in which large numbers of species ultimately die – become extinct.

Mechanism: A process, technique, or system for achieving a result.

Mechanistic: Determined by physical processes alone.

Mendelian Inheritance (Mendelism): The system of particulate inheritance acting through units or genes. Theoretical term.

Mendel’s Laws of Inheritance (Classical Genetics): First Law: Genes are transferred as separate and distinct units from one generation to the next; Second Law: The allele pairs separate during the formation of gametes and are transmitted independently of one another. Theoretical term.

Mesozoic Era: The age of dinosaurs that lasted from 245–65 million years ago. Theoretical term.

Methodology: Rules employed for performing a procedure.

Microbiome: The collection of microbial organisms that live internally and externally upon larger organisms.

Microevolution: A change in allele frequencies that occurs over time within a population, also known as adaptation.

Microevolution: Change in allele frequencies in a population of organisms under selection and random genetic drift. Synonymous with adaptation. Theoretical term.

Migration: Movement to another place.

Mismatch: The lack of fit between an organism’s traits and environment.

Mitochondrion: An organelle in eukaryotic cells where cellular respiration takes place.

Modern Synthesis: The 20th-century synthesis theory of biological evolution reconciling Charles Darwin’s natural selection theory with Gregor Mendel’s laws of inheritance. Theoretical term.

Model: A research method using a mathematical model of equations to indirectly represents a real system. Theoretical term.

Molecule: an electrically neutral group of two or more atoms held together by chemical bonds.

Molecular: Relating to or consisting of molecules.

Molecular Biology: The branch of biology that studies the molecular basis of biological activity intersecting biochemistry and genetics.

Molecular Clock: Measures time interval between inferred evolutionary changes using molecular biology. Theoretical term.

Molecules: A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.

Molting: A process in which an animal sheds all or part of its outer covering, which is then regenerated in some way.

Monophyletic (monophylogeny): A group of organisms that are classified in the same taxon and share a most common recent ancestor; also known as a clade. Theoretical term.

Morphology: The field of biology that characterizes the relationship of structures in terms of shape, structure, color, pattern, size, rigidity, and other physical properties.

Most Recent Common Ancestor (MRCA): The youngest common ancestor that two taxa share. Theoretical term.

Multicellular: An organism that consists of multiple cells.

Multilevel Hierarchy: A hierarchy encompassing levels from small molecules to macromolecules; from macromolecules to functional complexes, subcellular compartments, and cells; from unicellular organisms to communities, consortia, and multicellularity; from simple multicellular organisms to highly complex forms with differentiated tissues; and from organisms to communities and eventually, to eusociality and to complex biocenoses involved in biogeochemical processes on the planetary scale. Theoretical term.

Multilevel Selection (MLS): Levels of selective mechanisms driving major inferred evolutionary transitions (MTE). Theoretical term.

Mutation: Change in DNA or RNA sequence of bases.

Mutualism: Symbiotic relationship in which both species benefit.

Nascent: Just coming into existence and displaying signs of future potential.

Natural Law: A universal explanation that predicts a natural phenomenon validated by repetitive objective observation.

Natural Resources: Natural beneficial elements.

Natural Selection: A speciation and extinction process; acceptable favorable characteristics are preserved while undesirable characteristics are rejected, resulting in extinction. A cornerstone of Charles Darwin‘s theory. Theoretical term.

Naturalism: The view that only natural laws and forces (as opposed to supernatural or spiritual ones) operate in the universe.

Neo-Darwinism: A modern version of Darwin’s theory of evolution by natural selection, incorporating the findings of genetics. Theoretical term.

Neutral Theory: The idea that most of the molecular variation within populations is not being selected for or against — changes in the nucleic acid sequences are random. Theoretical term.

Niche: Habitat in an ecosystem.

Niche Construction: The process by which an organism alters its own (or another species’) local environment.

Node: A point on a phylogeny where a single ancestral lineage breaks into two or more descendent lineages. Theoretical term.

Norm of Reaction: The way in which a genotype is expressed as a trait under different environmental circumstances.

Non-Random Mating: A mating system in which at least some individuals are more or less likely to mate with individuals of a particular genotype than with individuals of other genotypes. Theoretical term.

Nucleotide: The basic structural unit and building block for DNA hooked together to form a chain of DNA that is composed of 3 parts – 1) a five-sided sugar, 2) a phosphate group, and 3) nitrogenous bases, including Adenine (A), Cytosine (C), Guanine (G), and Thymine (T).

Obligate Trait: A non-adaptive phenotypic expression of the genotype. Theoretical term.

Observation: The action or process of observing something or someone carefully or in order to gain information:

Ontogeny: The developmental history of an organism within its own lifetime, also known as life history.

Order: The level of classification or taxonomic rank below class and above family. Theoretical term.

Organelle: Subunit within a cell that has a specific function.

Organic: Relating to or derived from living matter.

Organic Compound: In chemistry, chemical compounds contain carbon-hydrogen bonds.

Organic Matter: Substance from a once-living organism is capable of decay or is the product of decay, or is composed of organic compounds.

Organism: A living system functioning as an individual entity.

Origin of Life: Transition from inorganic matter to an organized self-sustaining mechanism of organic molecules collaborating within a cellular structure to perpetually reproduce.

Origin of Species: Charles Darwin’s most influential book proposes a natural process for the origin of species. Click for extended coverage.

Orthogenesis: Organisms have an innate tendency to evolve in a definite direction towards some goal (teleological) due to some internal mechanism or “driving force.” Also known as orthogenetic evolution, progressive evolution, evolutionary progress, or progressivism. Theoretical term.

Orthologous: Diverging after a speciation event. Theoretical term.

Paleo: Ancient; often used as a suffix meaning ancient, e.g., paleobiology, paleogeography.

Paleoanthropologist: A paleontologist that studies fossils of humans and their closest relatives.

Paleontology: Study of life that once existed on Earth.

Paleozoic Era: Age of “old life” from 544–245 million years ago, beginning with the Cambrian explosion and ending with the Permian extinction. Theoretical term.

Pangenesis. Charles Darwin’s hypothetical mechanism for heredity, in which he proposed that each part of the body continually emitted its type of small organic particles called gemmules that aggregated in the gonads. Theoretical term.

Panspermia: View that life on Earth originated in outer space delivered by meteors. Theoretical term.

Paralogous: Divergence within a species. Theoretical term.

Paraphyletic (paraphyly): A group consisting of a last common ancestor of all of its members, but does not include all of the descendants of that most recent common ancestor. and most of its descendants, Theoretical term.

Parasite: Organism that lives on or within another organism [host organism] on which it feeds.

Parapatric Speciation: A mode of speciation in which two subpopulations of a species evolve reproductive isolation from one another while continuing to exchange genes. Theoretical term.

Parsimony: The problem-solving principle in which the simplest explanation accounting for the observations is the preferred explanation; a principle of phylogenetic tree reconstruction in which the phylogeny of a group of species or genes is inferred to be the branching pattern. Theoretical term.

Peripatric Speciation: A mode of speciation in which a new species is formed from an isolated peripheral population. Theoretical term.

Permian Extinction: Largest known extinction event occurring at the end of the Paleozoic Period. Theoretical term.

Phenetic Species: Organisms classified based on overall similarities. Theoretical term.

Phenomics: The systematic measurement and analysis of qualitative and quantitative traits, including clinical, biochemical, and imaging methodologies, for the refinement and characterization of a phenotype.

Phenotype: The observable characteristics of an organism.

Phenotypic Plasticity: The ability to change its phenotype in response to biospheric changes.

Phenotypic Variation: The differences in phenotype among individuals of the same species.

Philosophy: The study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language.

Phylogenetic Tree: A diagram or description of a tree portraying inferred evolutionary relationships between different organisms over time; the inferred common ancestor(s) as the trunk and nodes, species on branch ends, Theoretical term.

Phylogenetic: Inferred evolutionary history of a group of organisms based on based on similarities and differences; often used interchangeable with phylogeny. Theoretical term.

Phylogenetic Classification: A system of classification that names groups of organisms according to their inferred evolutionary history. Theoretical term.

Phylogenetic Species Concept (PSC): A distinctive reproductive group of inferred descendants from a common ancestor possessing a specific combination of defining traits. (see apomorphy).

Phylogeny: Inferred evolutionary relationships of a group of similar organisms; often used interchangeable with phylogenetic. Theoretical term.

Phyletic Speciation: One lineage gradually changes over time into a new and distinct form without increasing the number of resultant species. Theoretical term.

Phylum: The level of classification or taxonomic rank below kingdom and above class. Theoretical term.

Physiology: The scientific study of functions and mechanisms in a living system.

Pigment: Substance that absorbs light. Pigments absorb light of particular wavelengths, which gives the pigment a characteristic color.

Placenta: The organ that connects a fetus to the wall of its mother’s uterus.

Plasticity: The quality of being easily shaped or molded

Plate Tectonics: The massive-scale geological subduction and lifting movement of Earth’s plates resulting in the release of massive-scale subterranean water, volcanic lava, volcanic ash, and gases. Evidence compatible with the Genesis chapter 7 account written by Moses.

Pleiotropy: A single gene affects more than one trait.

Ploidy: The number of copies of each chromosome an organism carries.

Point Mutation: Change in a single nucleotide base in the genetic material.

Polygenic Characteristic: A phenotype influenced by more than one gene.

Polymorphic: Occurring in several different forms, in particular concerning species or genetic variation.

Polyphyletic: A group of organisms arising from multiple ancestral sources and therefore not suitable for placing in the same taxon:. Theoretical term.

Polytomy: A node on a phylogeny where more than two lineages descend from a single ancestral lineage. Theoretical term.

Population: All the organisms of the same species living in the same area.

Population Genetics: Genetic differences within and between populations.

Population Bottleneck: An event in which a population’s size is greatly reduced.

Population Growth Rate: the increase in the number of individuals in a population.

Populations: Inhabitants of a defined space.

Predator: An organism that hunts and eats other organisms.

Prediction: Forecast of what will happen.

Presupposition: A thing tacitly assumed beforehand at the beginning of a line of argument or course of action.

Prey: Organism killed for food by a predator.

Primordial: Having a chemical composition close to the original composition of the material from which the Solar System formed.

Primordial Soup: A nickname for the theory that life originated from synthesizing organic molecules in the ocean. Theoretical term.

Probability: Numerical description of how likely an event will occur.

Progeny: An offspring collective, also known as a brood.

Prokaryote: A single-celled (unicellular) organism without a nucleus and classified into bacteria and archaea.

Protein: A molecule made of a string of amino acids, folded into a complex three-dimensional structure. Proteins are coded for by DNA and are essential molecules for life.

Protozoa: A group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris.

Punctuated Equilibrium: Long periods of stasis interrupted by bursts of rapid change. Theoretical term.

Quantitative Genetics: The study of the genetic basis of traits that vary continuously (in characters such as height or mass)—as opposed to discretely identifiable phenotypes and gene-products (such as eye color, or the presence of a particular biochemical).

Race: A way of classifying humans into large groups based on inherited characteristics. Theoretical term.

Radial Symmetry: A property of an item (e.g., a shape or an animal) that can be divided into two matching halves by many different lines, which all intersect one another at a single point in the center. Theoretical term.

Radiocarbon Dating: A method for determining the age of an object using a radioactive isotope of carbon.

Radiometric Dating: A method of dating geological or archeological specimens by determining the relative proportions of particular radioactive isotopes present in a sample (for extended coverage, clink on the term).

Random: Made, done, happening, or chosen without method or conscious decision.

Range: The region throughout which a kind of organism or ecological community naturally lives or occurs.

Realized Niche: Range of environmental conditions in which a species live.

Reason: The capacity of applying logic using information to draw conclusions.

Reasoning: A process of extrapolating reason to generate new understandings.

Recessive Gene: Gene version with an effect that is only observed when it is found paired with an identical version in the same individual.

Recombination: A process in which pairs of chromosomes swap DNA with one another.

Reductive evolution: Inferred process by which microorganisms remove genes from their genome. Theoretical term.

Regulatory Element: Region of DNA where a regulatory protein binds.

Regulatory Gene: A gene that controls when protein-coding genes are turned on or off.

Regulatory Protein: A protein that regulates gene expression.

Relative Dating: Method of dating fossils by their location in rock layers; determines which fossils are older or younger but not their age in years.

Relativity: Encompasses two interrelated physics theories by Albert Einstein: special relativity and general relativity,

Renormalization: A statistical description of faster-changing (higher-frequency) variables is feasible through the slower-changing (lower-frequency) variables.

Replication: Reproductive process using integrated metabolic and information networks to develop building blocks, repair, and elimination mechanisms of the corresponding information-processing units (IPUs) on every level of organization.

Replicator Theory: Inferred coevolution of genes and memes. Theoretical term.

Reproduction: Process giving rise to the next generation.

Reproductive Isolation: Prevent members of different species from producing offspring, or ensure that any offspring are sterile. Theoretical term.

Retrogression: The process of returning to an earlier state.

Ribosomal RNA: Type of RNA that helps form ribosomes and assemble proteins.

Ribosome: A macromolecular machine that performs biological protein synthesis (mRNA translation).

RNA (ribonucleic acid): Single-stranded nucleic acid produces proteins to perform various biological roles in coding, decoding, regulating, and expressing genes.

RNA World Hypothesis: Life on Earth began with self-replicating RNA molecules. Theoretical term.

Royal Society: Established in 1660 by King Charles II, the Royal Society of London has served as the oldest continuously existing society to advance the principles of science – known as the scientific method.

Royal Medal: Award was created by George IV in 1826 by the Royal Society, two for “the most important contributions to the advancement of natural knowledge” and one for “distinguished contributions in the applied sciences”, done within the Commonwealth of Nations.

Rudimentary: an immature, undeveloped, or basic form. Theoretical term.

Saltationism: A sudden and large mutational change from one generation to the next, potentially causing single-step speciation.

Science: A systematic enterprise that builds and organizes knowledge.

Scientific Investigation: A systematic enterprise to characterize causal relationships.

Scientific Law: A universal statement and/or mathematical equations that precisely predicts a natural phenomenon validated by repetitive and testable objective observations.

Scientific Method: An empirical method of observation, measurement, and experimentation to formulate, test, and inductively develop hypotheses on the principles of nature.

Scientific Name: Synonymous with species’ binomial name.

Second Law of Thermodynamics: The entropy of isolated systems cannot decrease with time, as they always arrive at a state of thermodynamic equilibrium, where the entropy is highest.

Sedimentary Rocks: The accumulation or deposition of mineral or organic particles followed by cementation.

Segregation: The process in which pairs of chromosomes separate and are shuttled off to different gametic daughter cells.

Sexual Selection: A mode of natural selection Darwin included in the Origin of Species to describe how members of the same sex compete for access to members of the opposite sex. Theoretical term.

Signal Detection: The ability of individuals to detect signaling behavior from other individuals.

Single Cell: An organism consisting of one cell, such as bacteria, protozoa, and some algae, fungi, and yeasts; also known as a prokaryotic organism.

Single Nucleotide Polymorphism: A variation at a single, specific location in the genome

Sister Groups: Clades that are each other’s closest relatives. Theoretical term.

Somatic Mutation: Mutations that occur in non-reproductive cells of the body.

Spacetime: A mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum.

Special Relativity: The relationship between space and time.

Specialization: An organ or part to serve a special function.

Speciation: A process by which a single species evolves into two or more distinct sustaining life-forms; a major transition in evolution (MTE). Theoretical term.

Species: Distinct life-forms that rank next below the genus group; the basic rank of zoological classification defined by the International Code of Zoological Nomenclature

Species Concept: A biological principle distinguishing distinct life-forms in Earth’s biosphere.

Stabilizing Selection: Type of natural selection that favors the average of the characteristics. Theoretical term.

Stratigraphy: The geological study of strata’s order and relative position and their relationship to a geological time scale.

Stratum: A layer of sedimentary rock.

Subspecies: Groups within a species that have distinct forms and live in a restricted area. Theoretical term.

Superposition: The idea that older rock layers or strata were deposited earlier and so will generally be found beneath younger strata.

Symbiont: An organism that lives in close contact with another organism (usually with an organism of a different species).

Symbiosis: Any close and long-term biological interaction between two different biological organisms that are mutualistic, communalistic, or parasitic.

Sympatric Speciation: Two subpopulations of a species evolve reproductive isolation within the same geographical region. Theoretical term.

Synthetic Biology: Create new biological parts, devices, and systems or redesign systems found in nature. Theoretical term.

Taxon: A group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Theoretical term.

Taxonomic Rank: The biological classification by species, family, order, class, phylum, kingdom, and domain. Theoretical term.

Taxonomy: The classification and naming of organisms based on shared biological characteristics. Theoretical term.

Terminal Taxon: A clade, species, or lineage that appears at the tip of a phylogenetic tree. Terminal taxa may be extant or extinct. Theoretical term.

Testing: Observing and measuring values to compare with the expected values predicted by a hypothesis or theory.

Tetrapod: The animal clade containing vertebrates with sturdy legs (as opposed to fins).

Theory: For a hypothesis to be a scientifically valid theory, all evidence tested must be compatible with the hypothesis.

Theory of Evolution: A natural explanation for the origins of life on Earth and how new species have emerged over time while other species have become extinct.

Thermodynamics: The physics dealing with heat, work, and temperature and their relation to energy, radiation, and physical properties of matter.

Time: The universe’s fourth dimension of space, consisting of a continuous succession of moments of space streaming irreversibly from the beginning in one direction.

Timeframe: A specified time period in which some action or project happens.

Timeline: A chronological arrangement of events in the order of their occurrence:

Timescale: An arrangement of events used as a measure of the relative or absolute duration or antiquity of a period of history or geologic or cosmic time. The length of time during which it happens or develops. Several events marked in a broad span of time.

Timing: The specific moment or point in time when something happens.

Transcription: The sequential process of copying a segment of DNA into RNA.

Transfer RNA (tRNA): Carries amino acids to ribosomes for protein synthesis.

Transitional Links: An organism with intermediate features between its ancestor and offspring. Theoretical term.

Translation: The synthesis of specific proteins in ribosomes from DNA to RNA instructions – ribosomes and associated molecules are the translational apparatus.

Tree Thinking: Thinking of biodiversity emerging as a tree resulting from inferred evolution. Theoretical term.

Unicellular: A single-celled organism, unlike a multicellular organism that consists of multiple cells.

Uniformitarianism: View that all of Earth’s natural geological processes have continuously operated slowly and in the same manner as observed today – in contrast to catastrophic.

Universal Time (UT1): Time standard based on the average speed of the Earth’s rotation.

Use and Disuse: The view that animals acquire characteristics after using certain physical traits. Theoretical term.

Validity:

Variation: Any difference between cells, individual organisms, or groups of organisms of any species caused either by genetic differences (genotypic variation) or by the effect of environmental factors on the expression of the genetic potentials (phenotypic variation).

Vertebrate: Distinguished by the possession of a backbone or spinal column.

Vestigial Structures: Body parts that seemingly no longer have a purpose. Theoretical term.

Vicariance: A process in which a species’ range is divided even though the species has remained in place. Theoretical term.

Weismann Barrier: Demonstrated the difference between somatic and germ cells, undermined Lamarckian concepts of use and disuse.

Yeast: A eukaryotic, single-celled microorganisms classified as members of the fungus kingdom.

The first five editions of The Origin of Species did not include a glossary of terms. However, for only the 6^th edition published in 1872, Darwin approved the addition of a glossary written by W.S. Dallas.

Darwin entitled Dallas’ Glossary as –

“GLOSSARY OF THE PRINCIPAL SCIENTIFIC TERMS USED IN THE PRESENT VOLUME, SIXTH EDITION, 1872, in “THE ORIGIN OF SPECIES BY MEANS OF NATURAL SELECTION, OR THE PRESERVATION OF FAVOURED RACES IN THE STRUGGLE FOR LIFE.”

The practice of using vague terms is evidence of Enlightenment influences on Darwin’s approach to studying nature.

Darwin Then and Now is an educational resource on the intersection of evolution and science and the challenges facing the theory of evolution.

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