Evidence of Evolution

Voyage of the Beagle  Charles Darwin’s observations on a voyage around the world led to new ideas about species

Voyage of the Beagle

Darwin, Wallace, and Natural Selection  In 1858, Charles Darwin and Alfred Wallace independently proposed a new theory, that natural selection can bring about evolution

Descent with Modification  Darwin compared the modern armadillo with the extinct glyptodont

Variations in Traits  Darwin observed that variations in traits influence an individual’s ability to secure resources – to survive and reproduce

Theory of Natural Selection  Natural selection The differential in survival and reproduction among individuals of a population that vary in details of their shared traits Can lead to increased fitness  Fitness An individual’s adaptation to an environment, measured by its relative genetic contribution to future generations

Fossil Evidence  Fossils Physical evidence of life in the distant past  Found in stacked layers of sedimentary rock Younger fossils in more recently deposited layers Older fossils underneath, in older layers

Stratification

Fossilization

Interpreting the Fossil Record  The fossil record is incomplete  Favors species with hard parts, dense populations with wide distribution, and that persisted a long time

Plate Tectonics Theory  Movements of Earth’s tectonic plates rafted land masses to new positions  Pangea: First ancient supercontinent Gondwana (later southern supercontinent)  Movements had profound impacts on the directions of life’s evolution

Evidence of Drifting Continents  Evidence for plate tectonics theory Distribution of global land masses Global fossil distribution Magnetic rocks Seafloor spreading from mid-oceanic ridges

Drifting Continents

Biogeographical Evidence

Morphological Divergence  Homologous structures: Similar body parts that became modified differently in different lineages  Evidence of descent from a common ancestor

Comparative Morphological Evidence

Homologous Structures

Analogous Structures

DNA, RNA, and Proteins  Comparisons of DNA, RNA, and proteins reveal and clarify evolutionary relationships

Processes of Evolution

Rise of the Super Rats

Populations Evolve  Population Individuals of the same species in the same area Generally the same number and kinds of genes for the same traits  Gene pool All the genes of a population

Variation in Alleles  Individuals who inherit different combinations of alleles vary in details of one or more traits  Mutations are the original source of new alleles Lethal mutations result in death Neutral mutations neither help nor hurt

Phenotypic Variation in Populations

Microevolution  Changes in allele frequencies of a population Mutation Natural selection Genetic drift Gene flow

Natural Selection  Natural selection Differential survival and reproduction among individuals of a population that show variations in details of their shared traits (alleles)  Allele frequencies Maintained by stabilizing selection Shifted by directional or disruptive selection

Modes of Natural Selection

Peppered Moth

Pocket Mice

Stabilizing Selection: Birth Weight

Sexual Selection

Balanced Polymorphism

Genetic Drift  Genetic drift Random change in a population’s allele frequencies over time, due to chance Can lead to loss of genetic diversity  Most pronounced in small or inbred populations Bottleneck: Drastic reduction in population Founder effect: Small founding group

Gene Flow  Gene flow Movement of alleles into or out of a population by immigration or emigration Helps keep populations of same species similar  Counters processes that cause populations to diverge (mutation, natural selection, genetic drift)

Gene Flow Between Oak Populations

Reproductive Isolation  Individuals of a sexually reproducing species can produce fertile offspring, but are reproductively isolated  Reproductive isolating mechanisms evolve when gene flow between populations stops  Divergences may lead to new species

Mechanical Isolation

Behavioral Isolation

Allopatric Speciation  A geographic barrier stops gene flow between two or more populations of a species Example: Isolated continents or archipelagos  Genetic divergence and reproductive isolation give rise to new species

Allopatric Speciations

An Isolated Archipelago

Patterns of Macroevolution  Coevolution Close ecological interactions cause two species to act as agents of selection upon one another  Extinction Irrevocable loss of species Mass extinctions and recoveries have occurred several times in the history of life Most species that ever existed are now extinct

Coevolution

Adaptation to What?  Evolutionary adaptation Heritable traits that improve an individual’s chance of surviving and reproducing (under conditions that prevailed when genes evolved)