SCIENCE - an organized way of using evidence to learn about the natural world

EVOLUTION “descent with modification” - all life on earth shares a

common ancestorchange in gene frequencies of a population from generation

to generationObservations of the natural world from many fields of

science provide evidence of the pattern of changeEvolution by Natural Selection explains the process of

changeThis is the genius of Charles Darwin – a mechanism - natural

selection – which explains the observation that living things have and continue to change

SCIENTIFIC EVIDENCE*?

•DIRECT OBSERVATION • FOSSIL RECORD•HOMOLOGY•BIOGEOGRAPHY

*OBSERVATION OF THE NATURAL WORLD MADE WITH THE SENSES, FACTS, REPEATABLE

DIRECT OBSERVATION – guppies• Can we observe evolutionary change occurring in a changing environment?• GUPPIES – John Endler, University of California

DIRECT OBSERVATION – guppies• Can predation result in natural selection for color pattern in guppies?• Observations – guppies, Poecilia reticulate, Aripo River, Trinidad• No 2 male guppies have the same color pattern (genetic)• Females mate more frequently with brightly colored males• Being a brightly colored male increases the chance genes will pass to

the next generation but does it also increase the likelihood that the male will be eaten? Could the presence of predators influence the number of brightly colored males?

15 generations later – guppies transplanted from pike-cichlid pool to killifish pool

What if the guppies are returned to the source pool?

Can you discuss this in terms of natural selection?• Genetic variation• Overproduction of offspring• Struggle for existence• Differential survival and reproduction

What is sexual selection?

DIRECT OBSERVATION – drug resistant HIV• Can we observe evolutionary change occurring in a changing environment?

3TC LOOKS LIKE A BUILDING BLOCK OF DNA – ENZYME WILL ADD 3TC TO DNA IT IS BUILDING – STOPS DNA REPLICATION

DIRECT OBSERVATION – drug resistant HIV

3TC SHUTS THIS PROCESS DOWN

DIRECT OBSERVATION – drug resistant HIV• Is there genetic variation in virus?• 3TC resistant viruses already existed in the population of viruses• Being resistant is not an advantage until exposure to 3TC• Resistant viruses have a slightly different version of reverse transcriptase• Without 3TC they replicate more slowly than viruses with the typical version of the

enzyme

• Is there overproduction of offspring?• Is there a struggle for existence?• Is there differential survival and reproduction?

•Why does resistance develop so rapidly?• Viruses reproduce large

numbers of individuals very rapidly – even faster than bacteria• Viruses with a survival

advantage will increase in number very rapidly.

• Each year’s flu vaccine is slightly different because of this!

WHAT IS THE LESSON?• NATURAL SELECTION DOES NOT CREATE GENETIC VARIATION• IT DOES SELECT FOR INDIVIDUALS THAT HAVE A SURVIVAL

ADVANTAGE – genetic variation is inherent in populations.

• NATURAL SELECTION DEPENDS ON TIME AND PLACE•WHETHER OF NOT A GENETIC VARIATION PROVIDES AN

ADVANTAGE DEPENDS ON CURRENT, LOCAL ENVIRONMENT

FOSSIL RECORD• Fossils are physical evidence of organisms that lived in the past.• BE SURE TO READ ABOUT FOSSILS PAGE 453-453, FIGURE 22.3,

461-462

• Phil Gingrich made a whale of a discovery in 1978! Watch it here. ~ 5 minutes• http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_03

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