Mader Biology Ch 17 and 18 (and a little of 19) Evolution Mader Biology Ch 17 and 18 (and a little of 19)

Natural Selection Obs. 1: Individuals of a population vary phenotypically; no 2 are exactly alike Obs. 2: Much of this variation is heritable Inference #1: Those individuals whose heritable traits best fit them for the environment are likely to leave more offspring than less fit individuals Inference#2: This differential reproductive success will lead to a gradual change in a population

Summary of Darwin’s ideas Natural selection is differential success in reproduction It occurs through an interaction between the environment and the variability among individuals within a population The product of natural selection is the adaptation of populations to their environment

Natural Selection in Action

Natural Selection in Action Evolution of antibiotic-resistant strains of bacteria Industrial melanism in the peppered moth

Basic Vocabulary Natural Selection-a population of organisms can change over generations if individuals having certain heritable traits leave more offspring than others Adaptation- trait shaped by natural selection that increases an organism’s reproductive success (“fitness”). Ex- camouflage, mimicry Evolution- change in the genetic composition of a population over time

History of Evolutionary thought

Paleontology & Evolution Older layers of sedimentary rock (the layers on the bottom) contain fossil species very dissimilar from modern Each layer (stratum) is characterized by a unique group of fossil species As you move upward through the layers, you find species more and more similar to modern life

Based on paleontology, Lamarck proposed a theory of evolution Based on 2 mechanisms (1809) Use and disuse: the idea that parts used the most grow stronger; the parts that don’t get used deterioate Inheritance of acquired characteristics: the modification that an organism acquires during its lifetime can be passed along to its offspring Helped set stage for Darwin by proposing that species evolve as a result of interaction with environment

Charles Darwin (1809-1882) Born in England, he had a consuming interest in nature that his dad did not like His dad sent him to medical school (at 16). Charles was bored and left He then enrolled at Christ College at Cambridge with the intent to become a clergyman He was invited along on a voyage to chart the South American coastline on board the HMS Beagle that lasted 5 years

The Origin of Species (1859) developed 2 main points Descent with modification The history of life is like a tree, with multiple branching and re-branching from a common trunk all the way to the tips of it youngest twigs; most branches are dead ends Natural selection and adaptation The concept of natural election is based on 5 observations made by Darwin and can be summarized in 3 inferences made from those observations

Evidence for evolution

Bacterial Resistance We can see evolution through antibiotic resistance The population of bacteria can change over time to be resistant to many different drugs

The Fossil Record Older and older fossilized organisms deeper into crust Found in sedimentary rock We can determine the age of fossils with carbon dating

Biochemistry Similarities in genes and proteins show relatedness Scientists can determine the evolutionary relatedness based on the DNA sequence

Embryology Many animal embryos (in the womb) look similar This suggests common ancestry

Comparative Anatomy Homologous Structures: Analogous Structures: Structures that are anatomically similar because the organisms share a common ancestor Analogous Structures: Structures that are anatomically similar but the organisms do not share a common ancestor Vestigial Structures: Physical features that are reduced and unused Were once used by ancestors but evolved to not need them

Mechanisms for Evolution (aka: how does it occur?)

Mechanisms for Evolution Mutations Gene Flow Genetic Drift Nonrandom Mating Bottleneck Effect Founder Effect Natural Selection

Mutation Changes in DNA introduce variation in a population

Natural Selection Stabilizing: Directional: Disruptive: Middle phenotype favored Population moves toward norm Directional: Extreme phenotype is favored Population shifts in that direction Disruptive: 2 or more extreme phenotypes favored Population splits

Reminder: INDIVIDUAL ORGANISMS DO NOT EVOLVE! Natural selection does not act on individuals, but only in the sense that it affects one individual’s ability to survive and reproduce The smallest unit that can evolve is a population, a collection of individuals of the same species living in an area together

Mechanisms of speciation How do new species occur?

Geographic Isolation Species occur in different areas Ammospermophilus spp Species occur in different areas physical barrier prevents gene flow Harris’s antelope squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related white-tailed antelope squirrel

Reproductive Isolation