NATURAL SELECTION

EVOLUTIONEVOLUTION

the mechanism of evolution

organisms that are better suited to survive in a given organisms that are better suited to survive in a given environment are more likely to survive & reproduceenvironment are more likely to survive & reproduce

determines the differential survival of groups of organisms

creates biodiversity & variationbiodiversitybiodiversity = sum of diff kinds of ALL organisms in an ecosystem

Process of natural selection over time; Process of natural selection over time; genetic change (variety and diversity) combined with constantly changing environments

NATURAL SELECTIONNATURAL SELECTION

NATURAL SELECTIONElements required: Population is growing Variation among individuals in population That individual variation is heritable Stress or competition for resources (“struggle for

survival”)

ADAPTATION

Traits = GENETIC characteristic that helps an organism survive

Adaptive traits are helpful:they are “selected FORselected FOR” Ex/ Camouflage

Disadvantageous traits are NOT helpful; they are “selected AGAINSTselected AGAINST”Ex/ coloration that stands out

A feature produced or preserved by natural selection

ADAPTATION

Structural adaptations

•features of the organism;

•Ex/camouflage

Can be structural or behavioral

Behavioral adaptations

things the organism does to survive;

Ex/ migration

MORE ON ADAPTATIONMore diversity = increased chance that at least some individuals will adapt to survive future environmental change

1. diverse bacteria

2. ecological opportunity for antibiotic-resistant bacteria

3. new population of antibiotic-resistant bacteria

How are organisms “favored?”The organisms that are well-suited have advantageous traits (adaptations)

They are better at surviving and reproducing – so the traits (genetic change) is passed on

“selected FOR” example: camouflage

NATURAL SELECTION REVISTIED

Over time, populations evolve to have traits that are adapted to their environments.

The organisms that are not well-suited are not as well adapted,

and may die before they can pass their traits on to the next

generation

As an environment changes, the selection for

the adaptive traits is realigned with the change

NATURAL SELECTION CLASSIC EXAMPLE:Industrial Revolution & the Peppered Moth

2 varieties of moth: dark and light Pre-Industrial Revolution dark moth was rare During the Industrial Revolution light moth became rare WHY? Some moths had an adaptive advantage that fitness

Those adaptations were passed on and that trait was selected FOR.