Key Concepts in Biology and Evolution

anecdotal observation

An observation based on a single instance or a small number of instances, often leading to faulty conclusions because it lacks systematic testing and controls.

biological literacy

The ability to use the process of scientific inquiry to think creatively about real-world issues having a biological component and to communicate these thoughts to others.

biology

The scientific study of life.

blind experimental design

An experimental design in which the subjects do not know what treatment they are receiving.

control group

In an experiment, the group of subjects who are treated identically to the experimental group except that they don't receive the treatment.

critical experiment

An experiment that makes it possible to decisively determine whether a particular hypothesis is correct as it enables researchers to choose between alternative hypotheses.

dependent variable

A measurable effect, outcome, or response in which the research is interested. Its value is expected to change in response to the independent variable.

double-blind experimental design

An experimental design in which neither the subjects nor the experimenters know what treatment the subjects are receiving.

empirical

Based on experience and observations that are rational, testable, and repeatable.

experimental group

In an experiment, the group of subjects who are exposed to a particular treatment.

hypothesis (pl. hypotheses)

A proposed explanation for an observed phenomenon.

independent variable

A condition or factor that is manipulated by a scientist during an experiment to observe its effect on a dependent variable.

null hypothesis

A hypothesis that states there is no statistically significant relationship between two variables. It is often the hypothesis that researchers try to disprove or nullify.

placebo

A control substance that has no therapeutic effect, used in experiments to control for the placebo effect.

placebo effect

The phenomenon in which people respond favorably to any treatment, regardless of whether it has an active chemical property or not.

positive correlation

A relationship between two variables in which both variables increase or decrease together.

pseudoscience

Scientific-sounding claims that are not supported by trustworthy, methodical scientific studies.

randomized

In an experiment, the process of making random assignments of subjects to treatment and control groups.

replication

The process of repeating a study or experiment to verify the findings.

science

A process for understanding the world.

scientific literacy

The ability to understand, interpret, and apply scientific concepts and information.

scientific method

A body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge.

scientific theory

A hypothesis that has been so strongly and persuasively supported by empirical observation that the scientific community views it as very unlikely to be altered by new evidence.

scientific thinking

A process that uses observations and experiments to draw conclusions based on evidence.

statistics

A set of analytical and interpretive methods that help us make sense of a numerical data.

superstition

A belief or practice resulting from ignorance, fear of the unknown, trust in magic or chance, or a false conception of causation.

technology

The application of scientific knowledge for practical purposes.

treatment

Any experimental condition applied to research subjects.

variable

Any characteristic or property of an object, event, or phenomenon that can vary.

adaptation

Refers both to the process by which organisms can become better matched to their environment and to the specific traits that make an organism more fit.

artificial selection

A process by which animal breeders and farmers modify their animals and crops through selective breeding, essentially making use of natural selection.

biogeography

The study of the distribution of species and ecosystems in geographic space and through geological time.

bottleneck effect

A type of genetic drift that occurs when a population's size is sharply reduced due to some random event, leading to a loss of genetic variation.

convergent evolution

The process whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.

differential reproductive success

The situation in which individuals with one version of a heritable trait have greater reproductive success than do individuals with a different version of the trait. This is a key component of natural selection.

directional selection

A type of natural selection in which the average value for a trait in a population increases or decreases over time.

disruptive selection

A type of natural selection in which individuals with extreme phenotypes have the highest fitness.

evolution

A change in allele frequencies within a population.

fitness

A measure of the reproductive output of an individual with a particular phenotype, compared with the reproductive output of individuals with alternative phenotypes.

fixation

The point at which an allele becomes the only allele for a given gene in a population.

fossil

The preserved remains or traces of animals, plants, and other organisms from the remote past.

founder effect

A type of genetic drift that occurs when a small group of individuals migrates to a new area and establishes a new population, leading to a reduction in genetic variation compared to the original population.

gene flow

The movement of alleles from one population to another due to migration.

genetic drift

A random change in allele frequencies within a population, unrelated to the alleles' influence on reproductive success.

heritability

The ability of a trait to be passed down from one generation to the next.

homologous structure

Structures in different species that are similar because of common ancestry.

inheritance

The process by which genetic information is passed from parent to offspring.

migration

The movement of individuals into or out of a population, which can lead to a change in allele frequencies.

mutation

An alteration of the base-pair sequence in an individual's DNA. It is the only way that new alleles can be created within a population.

natural selection

A mechanism of evolution that occurs when there is heritable variation for a trait, and individuals with one version of the trait have greater reproductive success than do individuals with a different version of the trait.

population

A group of individuals of the same species that live in the same area and interbreed.

radiometric dating

A method of dating geological or archeological specimens by determining the relative proportions of particular radioactive isotopes present in a sample.

sexual selection

A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.

stabilizing selection

A type of natural selection in which the average value of a trait remains the same while extreme versions are selected against.

trait

A characteristic or feature of an organism.

vestigial structure

A feature that an organism has that is no longer useful, but was useful to its ancestors.

adaptive radiation

Brief periods of time during which a small number of species diversify into a much larger number of species, often triggered by mass extinctions, colonizations of new habitats, or evolutionary innovations.

allopatric speciation

A form of speciation that occurs when two populations of the same species become geographically isolated from one another, preventing gene flow and eventually leading to reproductive isolation.

analogous trait

A trait that is shared by two or more species, not because of common ancestry, but because of convergent evolution.

archaea

One of the three domains of life. They physically resemble bacteria but are more closely related to eukarya, and many are adapted to life in extreme environments.

background extinction

The rate at which species become extinct due to ordinary environmental changes or competition, as opposed to mass extinction events.

biological species concept

A definition of species as populations of individuals that either do or could interbreed, and that cannot interbreed with organisms from other such groups.

class

A taxonomic rank used in the classification of organisms, below phylum and above order.

domain

The highest taxonomic rank in the hierarchical classification of organisms, divided into Bacteria, Archaea, and Eukarya.

extinction

The complete disappearance of a species from Earth.

family

A taxonomic rank used in the classification of organisms, below order and above genus.

genetic divergence

The process by which two or more populations of an ancestral species accumulate independent genetic changes (mutations) through time, often leading to reproductive isolation.

genus (pl. genera)

A taxonomic rank used in the classification of organisms, below family and above species. It is the first part of the binomial name for a species.

homologous feature

A structure or trait that is shared by two or more species because it was inherited from a common ancestor.

horizontal gene transfer

The movement of genetic material between unicellular and/or multicellular organisms other than by descent.

hybrid

Offspring resulting from the interbreeding of two different species or two different varieties of the same species.

hybridization

The process of interbreeding individuals from genetically distinct populations or species to produce a hybrid.

kingdom

A taxonomic rank used in the classification of organisms, below phylum and above class.

life

Defined by the presence of self-replicating molecules and metabolism.

macroevolution

Evolutionary change at or above the species level, including the origin of new taxonomic groups and major evolutionary transformations.

mass extinction

Periods during which a large number of species on earth become extinct over a short period of time.

microbe

A microorganism, especially a bacterium causing disease or fermentation.

microevolution

Change in allele frequencies in a population over generations.

microsphere

A spherical aggregation of molecules, often made of lipids, that can form spontaneously in water and may have been precursors to the first cells.

monophyletic

A group of organisms that includes an ancestor and all of its descendants.

morphological species concept

A definition of species in terms of measurable anatomical criteria. It can be used for asexual and fossil species where the biological species concept is difficult to apply.

node

In an evolutionary tree, the point at which a single ancestral lineage splits into two or more descendant lineages.

order

A taxonomic rank used in the classification of organisms, below class and above family.

phylogeny

The evolutionary history of a group of organisms.

phylum

A taxonomic rank used in the classification of organisms, below kingdom and above class.

polyploidy

A condition in which an organism has more than two sets of chromosomes. It can lead to rapid speciation, especially in plants.

postzygotic barrier

A reproductive isolating mechanism that acts after fertilization, such as hybrid inviability or hybrid sterility.

prezygotic barrier

A reproductive isolating mechanism that prevents mating or fertilization from occurring.

protist

Any eukaryotic organism that is not an animal, plant, or fungus.

punctuated equilibrium

A hypothesis holding that the evolution of species proceeds in a characteristic pattern of long periods of little or no change (stasis), interrupted by brief periods of rapid change, often associated with speciation events.

reproductive isolation

The inability of individuals from two populations to interbreed and produce fertile offspring. It is a key factor in speciation.

ring species

A species that has a range that forms a ring around a geographical barrier, where adjacent populations can interbreed, but populations at the ends of the ring cannot.

speciation

The process by which one species splits into two distinct species that are reproductively isolated.

speciation event

A point in evolutionary history at which a given species splits into two or more distinct species.

species

Generally defined as populations of individuals that either do or could interbreed, and that cannot interbreed with organisms from other such groups. They are the basic units of biodiversity.

specific epithet

The second part of the binomial name for a species, unique to each species within its genus.

sympatric speciation

The process through which new species evolve from a single ancestral species while inhabiting the same geographic region.

systematics

The study of the diversification of living forms, both past and present, and the relationships among living things through time.

virus

A tiny, nonliving particle that invades and then reproduces inside a living cell.