Glossary

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Darwin, Charles
(1809-1882) a British naturalist who authored On the Origin of Species (1859); proposed the theory of natural selection which changed many biologists' views on evolution.
Darwinism
refers to the mechanisms of evolution as proposed by Charles Darwin in his book On the Origin of Species (1859), including the theory of natural selection.
dating techniques
a method of calculating the age of an event or organism; dates may be established through relative or absolute means.
death rate
the frequency of individuals in a population dying over a set period of time.
deciduous
lost during development; an anatomical reference to primary or "baby" teeth (deciduous dentition).
deletion
when one or more base pairs is removed from a sequence in DNA as a result of replication errors or mutations.
demography
a study of the increase or decrease in population size and what may have caused these changes (i.e., survival rates, death rates, reproduction, etc.).
dens
the odontoid process located on the second cervical vertebrae (the axis).
dental formula
a standardized notation for the total number of incisors, canines, premolars, and molars in the upper and lower jaw seen in an organism. An adult human dental formula is expressed as 2.1.2.3./2.1.2.3.
dentine

the chief tissue of a tooth; a tissue in the middle of the tooth that surrounds the pulp cavity and is covered by enamel on the crown and cementum on the root of the tooth.

dentition

teeth.

deoxyribonucleic acid
a nucleic acid based on the five-carbon sugar deoxyribose in a double helix formation; found within chromosomes that carries genetic information. See also DNA.
deposition
sediments accumulating on the surface of the earth.
derived trait

a recently acquired trait.

descent with modification
genetic material, including mutations, is pass from parent to offspring; the most basic principle of evolution.
Devonian
a period in the Paleozoic era on the geologic time scale that approximately dates from 395 million years to 345 million years; marked by a mass extinction event at the end of the period that affected coral reefs and small marine organisms; the first fossils evidence of terrestrial vertebrates appears in the Devonian period.
diagenesis
the physical, chemical and biological changes affecting a fossil after deposition.
diagnostic
refers to an artifact from a distinct time period and/or tool industry; a bone that is identifiable as a particular species.
diaphysis
primary ossification center, or shaft, of long bones.
diastema
a space between teeth.
digging stick

a tool used by hominins to access below ground plant parts such as roots and tubers; can be constructed of wood, bone, horn, or antler.

diploidy
the state of cells containing two copies of each chromosome. Humans are diploids.
directional selection
when one extreme is selected against, changing the average composition of the population by removing the variants at that one extreme.
discoids
irregular, bifacially worked tools that have a working edge around their full (or greater majority) circumference.
disconformity
a break in the geologic record; a line that separates a layer of sedimentary rock deposited over a layer of previously eroded sedimentary rock.
disruptive selection
when the mean is selected against, driving the extremes of the population farther and farther from each other; may ultimately split the population into two separate populations.
distal

a relative term used to describe a part of a limb that is farther from the attachment point to the trunk of the body; the opposite of proximal.

diurnal
refers to an organism whose primary activities are during daylight hours.
divergence
[syn. divergent evolution] when genetic or character differences accumulate causing members of the same species to become increasingly different; the opposite of convergent evolution.
DNA

the abbreviation for deoxyribonucleic acid.

DNA sequence
the order of nucleotides in DNA.
domestication
the process in which humans supervise and control characteristics of plants and animals.
dominant allele
an allele that is expressed in the phenotype regardless of is recessive alternative.
dorsal
a relative term used for quadrupedal organisms (those that travel on four legs) to describe features that are closer to the spine or back of the body; opposite of ventral. The term posterior is a synonym commonly used when referring to bipedal hominin anatomy.
dorsiflexion

flexing the foot upwards towards the leg.
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