2026 Honors Biology Evolution Study Guide

Vocabulary flashcards covering fossils, comparative anatomy, biochemistry, embryology, and the mechanisms of natural selection and evolution.

Relative Dating

A method of determining the age of a fossil by comparing its placement in rock layers (A-M) with that of fossils in other layers.

Absolute Dating

A technique used to determine the actual age of a rock or fossil by measuring the decay of radioactive isotopes, such as $C-14$.

Half-life

The amount of time it takes for half of a radioactive isotope in a sample to decay; for $C-14$, this period is $5700\,years$.

Homologous Structures

Body parts in different organisms that are similar in structure, providing evidence of a common ancestor even if they do not have the same function.

Analogous Structures

Structures in different organisms that lead to similar functions but are not derived from a common ancestor and therefore are not evidence for evolution.

Vestigial Structures

Remnants of organs or structures that had a function in an early ancestor but no longer serve a purpose, such as the pelvis and leg bones in whales or optic nerves in cavefish.

Comparative Biochemistry

The study of evolutionary relationships by comparing similarities in DNA and proteins, such as the amino acid sequences in Cytochrome C.

Cytochrome C

A protein involved in cellular respiration in all eukaryotic organisms, containing $104$ amino acids in humans, used to measure genetic relatedness.

Comparative Embryology

The comparison of early stages of development across different species to identify common ancestry and evolutionary patterns.

Natural Selection

The mechanism for evolution where organisms with favorable traits for their environment are more likely to survive and reproduce.

Variation

Differences in traits within a population, which serves as a necessary principle for natural selection and is primarily sourced from mutations.

Overproduction

A principle of natural selection where organisms produce more offspring than the environment can support, leading to a struggle for existence.

Adaptation

A specific trait that makes an organism better suited for surviving and producing offspring in its particular environment.

Descent with Modification

The process by which, over time, more individuals in a population will possess desirable adaptations as they are passed down to offspring.

Fitness

A measure of an organism's ability to survive and produce more offspring relative to other members of the population in a given environment.

Stabilizing Selection

A type of natural selection that occurs when intermediate phenotypes are more likely to survive and blend into the environment than extreme phenotypes.

Directional Selection

Natural selection that favors one extreme phenotype over another, causing the population's trait distribution to shift in that direction.

Disruptive Selection

Natural selection that favors individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes.

Gene Pool

The combined genetic information (all the alleles) of all the members of a particular population.

Allele Frequency

A measure of how common a specific allele is in a population, calculated by determining the ratio of that allele to the total number of alleles for that gene.

Hardy-Weinberg Principle

A principle describing five conditions (large population, no mutation, no migration, random mating, and no natural selection) required for a population to never evolve.

Genetic Drift

A change in allele frequencies due to chance events, which has a more significant impact on small populations than on large ones.

Gene Flow

The movement of alleles between populations, typically through the migration of individuals.

Sexual Selection

A process where certain traits increase an organism's mating success, thereby altering the gene pool.

Speciation

The evolutionary process by which one species separates and develops into two or more distinct species that can no longer interbreed.