Evolution by Natural Selection explains the process of change 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