Glossary
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Glossary Terms for letter: S
sagittal keel A slight ridge of bone found along the midline sagittal suture of the cranium, which is typically found on H. erectus skulls.
Sahelanthropus tchadensis The earliest pre-australopithecine species found in central Africa with possible evidence of bipedalism.
scientific law A theory that becomes absolutely true.
scientific method An empirical research method in which data is gathered from observations of phenomena, hypotheses are formulated and tested, and conclusions are drawn that validate or modify the original hypotheses.
sectorial (premolar) Refers to a premolar adapted for cutting.
secular trend A phenotypic change, such as an increase in height, due to multiple factors.
sedimentary Rock formed when the deposition of sediments creates distinct layers, or strata.
senescence Refers to an organism's biological changes in later adulthood.
sex chromosomes The pair of chromosomes that determine an organism's biological sex.
sexual dimorphism A difference in a physical attribute between the males and females of a species.
sexual selection The frequency of traits that change due to those traits' attractiveness to members of the opposite sex.
shovel-shaped incisors A dental trait, commonly found among Native Americans and Asians, in which the incisors' posterior aspect has varying degrees of concavity.
sickle-cell anemia A genetic blood disease in which the red blood cells become deformed and sickle-shaped, decreasing their ability to carry oxygen to tissues.
single nucleotide polymorphisms (SNPs) Variations in the DNA se-quence due to the change of a single nitrogen base; also known as point mutations.
sivapithecids Early Miocene apes found in Asia.
Sivapithecus A genus of Miocene sivapithecids, proposed as ancestral to orangutans.
skin reflectance Refers to the amount of light reflected from the skin that can be measured and used to assess skin color.
sociolinguistics The science of investigating language's social contexts.
somatic cells Diploid cells that form the organs, tissues, and other parts of an organism's body.
species A group of related organisms that can interbreed and produce fertile, viable offspring.
spontaneous mutation Random changes in DNA that occur during cell division.
stabilizing selection Selection against the extremes of the phenotypic distribution, decreasing the genetic diversity for this trait in the population.
Steno's law of superposition The principle that the lower the stratum or layer, the older its age; the oldest layers are at the bottom, and the youngest are at the top.
strata Layers of sedimentary rock, representing various periods of deposition.
stratigraphic correlation The process of matching up strata from several sites through the analysis of chemical, physical, and other properties.
stressors Any factor that can cause stress in an organism, potentially affecting the body's proper functioning and its homeostasis.
structural genes Genes coded to produce particular products, such as an enzyme or hormone, rather than for regulatory proteins.
structural proteins Proteins that form an organism's physical attributes.
sun protection factor (SPF) The rating calculated by comparing the length of time needed for protected skin to burn to the length of time needed for unprotected skin to burn.
superfoods Cereal grains, such as rice, corn, and wheat, that make up a substantial portion of the human population's diet today.
synonymous point mutation A neutral point mutation in which the substituted nitrogen base creates a triplet coded to produce the same amino acid as that of the original triplet.
systematics The study and classification of living organisms to determine their evolutionary relationships with one another.
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