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Relative dating

a technique used to determine which of the two fossils is older

Absolute dating

a techinque used to determine the age of a fossil

radioactive dating

an unstable chemical element that decays, or breaks down , into a different element or elements

half life

the length of time needed for half the atoms of a radioactive isotope to decay

fossil record

the millons of fossils that scientists have collected

relative dating

- rock layers on bottom are older than rock laers on top
- organisms in deeper layers are older than organisms in shallow layers
- the actual age of an organism and/ or rock can be determined by calculating the ratio of radioactive istope to stable material present in a sample

index fossils

fossils that are easy to identify and that we know the age of (because of radioactive dating) can be used to determine the age of a rock of any fossil

geologic time scale

-based on major organisms that dominated in the past
-eras and periods are major divisions

comparative anatomy

structural similarities link related species
-structures analogous/ homologous

analogous structure

-different ancestors
-"analogy"= like
-different underlying structures
-same function
-similar environment

homologous structure

-same ancestor
-"homo" same
-same underlying structure
-different functions
-difffent environments

comparative embryology

similar embryo development in closely related spaces

comparative biochemistry

-similar DNA sequences
-similar gene segments of the DNA
-code for similar traits
-in closely related spaces

plate techtonics

-geological theory
-continental masses that were one land mass that explains
-closely related species have common ancestors on now seperated continents


group of interbreeding individuals that live in the same place at the same time and compete with each other for food, water, and shelter

gene pool

all the genes present in a population

relative frequency

precentage of individuals with a particular allele

natural selection

goverened by genetics- the change in relative frequency of a gene in a given population leads to a change in population and may result in a new species


-DNA replication mistakes
-chemicals in the environment
-gene shuffling from sexual reproduction

directional selection

when individuals at one end of the curve have higher fitness than individuals in the middle or other end

stabilizing selection

when individuals near the center of the curve have higher fitness than individuals at either end of the curve

disruptive selection

when individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle

Hardy- Weinburg Principle

the allele frequency will remain constant if:
- there is random mating
-the population is large
- no movement in or out of the population
- no mutations
- no natural selection for or against any trait

genetic drift

changes in the gene pool due to:
- random mating
- over a long period of time
-no immigration of males and females
- no migration od males and females
- no natural selection for or against any trait


-over time
-new species
-by isolation
- natural barriers

geographic isolation

separation of organisms by geographic features
- lakes, oceans, rivers
-(may result in new species over time)

reproductive isolation

when two different species cannot mate and have successful offspring
-geographic barriers
-anatomy or physiology
-social behaviors

reproductive isolation

two organisms cannot mate
- separated by geographic boundaries
-anatomical differences
- physiological differences
-social behaviors


small changes over a long time

punctuated equilibrium

large changes happen rapidly- periods of no change

adaptive radiation

evolution of many branches of organisms from a single soure


-branch off
-homologous structures
-same origin
- same underlying structure
-different funcions


-come together
-analogous features
-from different origins
- similar environments
-similar functions
-different structures

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