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fossil

any preserved evidence of an organism

paleontologist

A scientist who studies fossils

relative dating

a method used to determine the age of rocks by comparing them with those in other layers

law of superposition

states that younger layers of rock are deposited on top of older layers

radiometric dating

Dating using decay of radioactive isotopes.

half-life

the amount of time it takes for half of the original isotope to decay

geological time scale

a record of Earth's history

epochs

last several million years, are the smallest units of geologic time

periods

last tens of millions of years, divisions of geologic time consisting of two or more epochs

era

lasts hundreds of millions of years, unit of geological time consisting of two or more periods

eon

longest unit of time in the geologic time scale and can include billions of years

Cambrian explosion

rapid diversification of most major animal groups marking the start of the Paleozoic era

K-T boundary

layer of iridium-rich material between rocks of the Cretaceous period and rocks of the Paleogene period that provides evidence of a meteorite impact

plate tectonics

describes the movement of several large plates that make up the surface of the earth

spontaneous generation

the idea that life arises from nonlife

theory of biogenesis

states that only living organisms can produce other living organisms

endosymbiont theory

the ancestors of eukaryotic cells lived in association with prokaryotic cells

artificial selection

the process of directed breeding to produce offspring with desired traits

natural selection

A natural process resulting in the evolution of organisms best adapted to the environment.

derived traits

newly evolved features, such as feathers, that do not appear in the fossils of common ancestors

ancestral traits

more primitive features, such as teeth and tails, that do appear in ancestral forms

evolution

cumulative changes in groups of organisms through time

homologous structures

anatomically similar structures inherited from a common ancestor

vestigial structures

structures that are the reduced forms of functional structures in other organisms

analogous structures

structures that can be used for the same purpose and can be superficially similar in construction but are not inherited from a common ancestor

embryo

an early, pre-birth stage of an organism's development

biogeography

a field of study of the distribution of plants and animals around the world

fitness

a measure of the relative contribution that an individual trait makes to the next generation

camouflage

adaptations that allow organisms to blend in with their environments

mimicry

one species evolves to resemble another

Hardy-Weinberg Principle

when allelic frequencies remain constant, a population is in genetic equilibrium

genetic drift

any change in the allelic frequencies in a population that results from chance

founder effect

change in allele frequencies as a result of the migration of a small subgroup of a population

bottleneck

process in which a large population declines in number, then rebounds

stabilizing selection

it operates to eliminate extreme expressions of a trait when the average expression leads to higher fitness

directional selection

occurs when natural selection favors one of the extreme variations of a trait

disruptive selection

a process that splits a population into two groups

sexual selection

change in frequency of a trait is based on the ability to attract a mate

prezygotic isolating mechanisms

operate before fertilization occurs

postzygotic isolating mechanisms

operate after fertilization has occurred to ensure that the resulting hybrid remains infertile

allopatric speciation

a physicals barrier divides one population into two or more populations

sympatric speciation

a species evolves into a new species without a physical barrier

adaptive radiation

An evolutionary pattern in which many species evolve from a single ancestral species very quickly

gradualism

The theory that evolution occurs slowly but steadily

punctuated equilibrium

Pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change

opposable first digit

either a thumb or a great toe, is set apart from the other digits

binocular vision

forward-looking overlapping fields of vision

diurnal

active during the day

nocturnal

active at night

arboreal

tree-dwelling

anthropoids

large brained, diurnal monkeys and hominoids

prehensile tail

a tail that functions like a fifth limb

hominins

humanlike primates that appear to be more closely related to present-day humans than they are to present-day chimpanzees and bonobos

Hominoids

all nonmonkey anthropoids

bipedal

the ability to walk upright on two legs

australopithecines

small apelike brains and jaws with teeth and limbs that were humanlike

homo

living and extinct humans

Neanderthals

Homo sapiens neanderthalensis, a European variant of Homo sapiens that died out about 25,000 years ago.

cro-magnons

first fully modern humans

classification

the grouping of objects or organisms based on a set of criteria

taxonomy

a discipline of biology primarily concerned with identifying, naming, and classifying species based on natural relationships

bionomial nomenclature

gives each species a scientific name that has two parts

taxon

a named group of organisms

genus

a group of species that are closely related and share a common ancestor

family

Group of genera that share many characteristics

order

contains related families

class

contains related orders

phylum or division

contains related classes

phylogeny

Evolutionary history of a species

characters

inherited features that vary among species

molecular clock

a model that is used to compare DNA sequences from two different species to estimate how long the species have been evolving since they diverged from a common ancestor

cladistics

method that classifies organisms according to the the order that they diverged from a common ancestor

cladogram

a branching diagram that represents the proposed phylogeny or evolutionary history of

archaea

the species classified in domain archaea

protists

eukaryotic organisms that can be unicellular, colonial, or multicellular

fungus

Saprophytic and parasitic spore-producing eukaryotic organisms that lack chlorophyll and include molds, rusts, mildews, smuts, mushrooms, and yeasts.