SCIENCE - an organized way of using evidence to learn about
the natural world
EVOLUTION
 “descent with modification” - all life on earth shares a
common ancestor
change in gene frequencies of a population from generation
to generation
Observations of the natural world from many fields of
science provide evidence of the pattern of change
Evolution by Natural Selection explains the process of
change
This 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
4_05.html