 1) How old is the earth?  2) What is evolution?  3) How do you think all the species present on the earth got here?

 Comparative morphologists study body plans and structures among groups of organisms  Some organisms are outwardly similar, but different internally; others differ outwardly, but have similar internal structures  Some organisms have vestigial parts with no apparent function

 By the 1800s, many scholars realized that life on Earth had changed over time  Catastrophism  Georges Cuvier proposed that many species that once existed became extinct due to catastrophic geological events unlike those known today.

 Born in England – 1809  Sailed on the HMS Beagle’s five-year voyage mapping the coastline of South America.  Observed and recorded characteristics of species on the trip  Developed a scientific theory of biological evolution - explains how modern organisms evolved over long periods of time through descent from common ancestors.  Wrote On the Origin of Species  Darwin's Finches Darwin's Finches

 Species vary globally  Species vary locally  different, yet related, animal species often occupied different habitats within a local area  Species vary over time

 Different, yet ecologically similar, animal species inhabited separated, but ecologically similar, habitats around the globe ▪ found flightless, ground-dwelling birds that were similar on different continents. ▪ South America = rheas ▪ Africa = ostriches ▪ Australia = emu.

 Different, yet related, animal species often occupied different habitats within a local area ▪ Galapagos Islands – the shape of the tortoises’ shells corresponds to different habitats. ▪ Isabela Island has high peaks, is rainy, and has abundant vegetation that is close to the ground. A tortoise from Isabela Island has a dome-shaped shell and short neck. ▪ Hood Island, in contrast, is flat, dry, and has sparse vegetation. A long neck and a shell that is curved and open around the neck and legs allow the Hood Island tortoise to reach sparse, high vegetation.

 Darwin collected fossils = the preserved remains or traces of ancient organisms.  Darwin noticed that some fossils of extinct animals were similar to living species.  He discovered fossils of Glyptodont where armadillos currently live. ▪Why did Glyptodont disappear? ▪Why did they resemble armadillos?

 Hutton and Lyell - geologists  The earth is extremely old  Processes that changed the past are the same that operate in the present

 Lamarck – Although his ideas were FLAWED they shaped Darwin’s thinking  Organisms could change during their lifetimes by selectively using or not using various parts of their bodies  Individuals could pass these acquired traits on to their offspring, enabling species to change over time.  Organisms have an inborn urge to become more complex and perfect, and to change and acquire features that help them live more successfully in their environments.

 Malthus = if the human population grew unchecked, there wouldn’t be enough living space and food for everyone ▪ War, famine and disease would work against population growth  Darwin realized that most organisms don’t survive and reproduce, he wondered which individuals survive…and why?

 Natural selection  Differential survival and reproduction among individuals of a population that vary in details of shared, inherited traits  Adaptive trait  Any trait that enhances an individual’s fitness (ability to survive and reproduce in a particular environment)

 Natural selection = the process by which organisms with variations most suited to their environment survive and leave more offspring  Natural selection occurs when there is  1) A struggle for existence – more offspring are produced than can survive  2) Variation and adaptation  3) Survival of the fittest

 Grasshoppers can lay more than 200 eggs at a time, but only a small fraction of these offspring survive to reproduce.

 Adaptation = heritable characteristic that increases an organism’s ability to survive and reproduce in its environment ▪ EX. Green color is an adaptation: The green grasshoppers blend into their environment and so are less visible to predators.

 Fitness = the ability of an organism to survive and reproduce ▪ Because their color serves as a camouflage adaptation, green grasshoppers have higher fitness and so survive and reproduce more often than yellow grasshoppers do.

 Green grasshoppers become more common than yellow grasshoppers in this population over time.  More grasshoppers are born than can survive  Individuals vary in color and color is a heritable trait  Green grasshoppers have higher fitness in this particular environment

 Natural selection does not make organisms “better”.  It is a process that enables organisms to survive and reproduce in a local environment.  If local environmental conditions change, some traits that were once adaptive may no longer be useful  Salamander Evolution Salamander Evolution

18.1 Individuals Don’t Evolve, Populations Do  Evolution starts with mutations in individuals; mutation is the source of new alleles  Sexual reproduction can quickly spread a mutation through a population  Population  Individuals of the same species in the same area

Variation In Populations  All individuals of a species share certain traits  Individuals of a population vary in the details of their shared traits

The Gene Pool  Gene pool  All genes found in one population  Alleles  Different forms of the same gene  Determine genotype and phenotype  Dimorphism (2 alleles) and polymorphism (many alleles)

Key Events in Inheritance

 Mutations are the source of new alleles that give rise to differences in details of shared traits  Lethal mutations usually result in death  Neutral mutations have no effect on survival or reproduction  Beneficial mutations convey an advantage

Stability and Change in Allele Frequencies  Allele frequencies  Relative abundance of alleles of a given gene in a population  Natural populations are never in genetic equilibrium  A theoretical state which occurs when a population is not evolving

Microevolution  Four processes of microevolution (small-scale changes in a population's allele frequencies) prevent genetic equilibrium  Mutation  Natural selection  Genetic drift  Gene flow

Genetic Equilibrium  Five conditions required for a stable gene pool:  Mutations do not occur  Population is infinitely large  No gene flow  Random mating  All individuals survive and reproduce equally

The Hardy-Weinberg Formula  The Hardy-Weinberg formula can be used to determine if a population is in genetic equilibrium p 2 (AA) + 2pq (Aa) +q 2 (aa) = 1.0  The frequency of the dominant allele (A) plus the recessive allele (a) equals 1.0 p + q = 1.0

A Population in Equilibrium

 The number of phenotypes produced for a trait depends on how many genes control the trait.  A single-gene trait is a trait controlled by only one gene ▪ Single-gene traits may have just two or three distinct phenotypes.  Polygenic traits are traits controlled by two or more genes. ▪ A single polygenic trait often has many possible genotypes and even more different phenotypes.

18.4 Directional Selection  Directional selection  Changing environmental conditions can shift allele frequencies in a consistent direction  Forms of traits at one end of a range of phenotypic variation become more common

Predation and Peppered Moths  Light color is adaptive in areas of low pollution; dark color is adaptive in areas of high pollution

Predation and Rock-Pocket Mice  In rock-pocket mice, two alleles of a single gene control coat color  Night-flying owls are the selective pressure that directionally shifts the allele frequency

Antibiotic Resistant Bacteria  A typical two-week course of antibiotics can exert selection pressure on over a thousand generations of bacteria  Antibiotic resistant strains are now found in hospitals and schools

Stabilizing Selection: Body Weight of Sociable Weavers  Stabilizing selection  Natural selection that favors an intermediate phenotype and eliminates extreme forms

Disruptive Selection  Disruptive selection  Natural selection that favors extreme forms of a trait and eliminates the intermediate forms