Chapter 11 and 12 Vocab 2

Important Evolution Vocab

Gene pool

The combined alleles of all of the individuals in a population. Different combinations of alleles in a gene pool can be formed when organisms mate and have offspring.

Allele frequency

A measure of how common a certain allele is in the population.

Normal distribution

Type of distribution in which the frequency is highest near the mean value and decreases toward each extreme end of the range.

Microevolution

The observable change in the allele frequencies of a population over time.

Directional selection

A type of selection that favors phenotypes at one extreme of a trait's range.

Stabilizing selection

During this, the intermediate phenotype is favored and becomes more common in the population.

Disruptive selection

Occurs when both extreme phenotypes are favored, while individuals with intermediate phenotypes are selected against by something in nature.

Gene flow

The movement of alleles from one population to another.

Genetic drift

Changes in allele frequencies that are due to chance.

Bottleneck effect

Describes the effect of a destructive event that leaves only a few survivors in a population.

Founder effect

Genetic drift that occurs after a small number of individuals colonize a new area. The gene pools of these populations are often very different from those of the larger populations.

Sexual selection

Occurs when certain traits increase reproductive success. There are two types of sexual selection.

Hardy-Weinberg equilibrium

Populations that meet these conditions are not evolving: • Very large population No genetic drift can occur. • No emigration or immigration No gene flow can occur. • No mutations No new alleles can be added to the gene pool. • Random mating No sexual selection can occur. • No natural selection All traits must equally aid in survival.

Reproductive isolation

Occurs when members of different populations can no longer mate successfully.

Speciation

The rise of two or more species from one existing species.

Behavioral isolation

Isolation caused by differences in courtship or mating behaviors.

Geographic isolation

Involves physical barriers that divide a population into two or more groups. These barriers can include rivers, mountains, and dried lakebeds.

Temporal isolation

Exists when timing prevents reproduction between populations.

Convergent evolution

Evolution toward similar characteristics in unrelated species.

Divergent evolution

When closely related species evolve in different directions, they become increasingly different through this.

Coevolution

The process in which two or more species evolve in response to changes in each other.

Extinction

The elimination of a species from Earth. This often occurs when a species as a whole is unable to adapt to a change in its environment.

Punctuated equilibrium

States that episodes of speciation occur suddenly in geologic time and are followed by long periods of little evolutionary change, or stasis.

Adaptive radiation

The rapid evolution of many diverse species from ancestral species.

Relative dating

Estimates the time during which an organism lived by comparing the placement of fossils of that organism with the placement of fossils in other layers of rock.

Radiometric dating

A technique that uses the natural decay rate of unstable isotopes found in materials in order to calculate the age of that material.

Isotope

Atoms of an element that have the same number of protons but a different number of neutrons. Most elements have several of these.

Half-life

The amount of time it takes for half of the isotope in a sample to decay into a different element, or its product isotope.

Index fossil

Fossils of organisms that existed only during specific spans of time over large geographic areas.

Geologic time scale

A representation of the history of Earth. It organizes Earth's development by major changes or events that have occurred, using evidence from the fossil and geologic records.

Era

Last tens to hundreds of millions of years and consist of two or more periods.

Period

The most commonly used units of time on the geologic time scale, lasting tens of millions of years. Each of these is associated with a particular type of rock system.

Epoch

The smallest units of geologic time and last several million years.

Nebula

A cloud of gas and dust in space.

Ribozyme

RNA molecules that can catalyze specific chemical reactions.

Cyanobacteria

Bacteria that can carry out photosynthesis. Like all early life forms, each of these were a single prokaryotic cell.

Endosymbiosis

A relationship in which one organism lives within the body of another—with both organisms benefitting.

Paleozoic

Multicellular organisms first appeared during this era, which began 542 million years ago. The era ended 251 million years ago with a mass extinction. More than 90 percent of marine species and 70 percent of land species of that time became extinct. In between these remarkable events, multicellular animals radiated, the first vertebrates evolved, and early plants moved onto land.

Cambrian explosion

During this, a huge diversity of animal species evolved.

Mesozoic

This era began 251 million years ago and ended 65 million years ago. Called the Age of Reptiles because the dinosaurs roamed Earth during this era, this era also featured birds and flowering plants. The oldest direct ancestor of mammals first appeared during this era. This era is also divided into three periods: the Triassic- the Jurassic- and the Cretaceous.

Cenozoic

This era began 65 million years ago and continues today. It is divided into two periods, the Tertiary (65-1.8 million years ago), and the Quaternary (1.8 million years ago until today). The earliest ancestors of modern humans evolved near the end of the Tertiary. However, anatomically modern humans did not appear until very recently in Earth's history, nearly 200,000 years ago.

Primate

These make up a category of mammals with flexible hands and feet, forward-looking eyes— which allow for excellent three-dimensional vision—and enlarged brains relative to body size. These also have arms that can rotate in a circle around their shoulder joint, and many have thumbs that can move against their fingers.

Prosimian

These make up the oldest living primate group, and most are small and active at night.

Anthropoid

These are the humanlike primates, which are further subdivided into the New World monkeys, Old World monkeys, and hominoids.

Hominid

Include orangutans, chimpanzees, gorillas, and humans, but not gibbons. The term hominin refers only to modern humans and their immediate ancestors.

Bipedal

Animals that can walk on two legs. This trait has important adaptive advantages for higher primates. It allows higher reach into tree branches while foraging, and perhaps most importantly, it frees the hands for foraging, carrying infants and food, and using tools.