Chapter 16 The Theory of EvolutionThe Theory of Evolution What You’ll Learn What did Charles Darwin Contribute to Science? What are the Patterns of biodiversity Darwin noted?

Evolution: process of change through time  The change in characteristics of populations through generations. Thus, existing life forms have evolved from earlier life forms  A unifying principle for biology.  Provides an explanation for the difference in structure, function, and behavior among organisms

Fossils shape ideas about evolution Fossils: direct or indirect remains of organisms preserved in media such as sedimentary rock, amber, ice, or tar Ammonite casts –Fossilized organic matter in a leaf Ice Man”

Fossils shape ideas about evolution  When geologists provided evidence indicating that Earth was much older than many people had originally thought, biologists began to suspect that species change over time, or evolve

 A sea voyage helped Darwin frame his theory of evolution  The voyage of the Beagle 1831, ship’s naturalist

 Charles Darwin observed Species vary globally ○ Different, yet ecologically similar, animal species inhabited separated, but ecologically similar habitats. Species vary Locally ○ Different, yet related, animal species often occupied different habitats within a local area. Species vary over time ○ Some fossils of extinct animals were similar to living species

Ideas Influencing Darwin  Hutton and Lyell concluded that Earth is extremely old and the processes that changed Earth in the past are the same processes of the present – Uniformitarianism  Lamarck suggested that organisms could change by selectively using or not using traits and passing those acquired traits to their offspring. This caused them to change over time.

Malthus  Reasoned that if the human population grew unchecked, there wouldn’t be enough living space and food for everyone.  Darwin applied this idea to other organisms.

Artificial Selection  Darwin studied changes produced by plant and animal breeders.  Some of these variations can be passed from parents to offspring to improve crops and livestock.  Humans select the useful traits.

Evolutionary theory  Darwin became convinced that the Earth was old and continually changing He concluded that living things also change, or evolve over generations He also stated that living species descended from earlier life-forms: descent with modification

Darwin’s Ideas 1. The Struggle for existence If more individuals are produced than can survive, a population must compete for food, living space, and other resources. 2. Variation and Adaptation Some traits enable a species to survive better than others. Those species survive and pass those desirable traits to their offspring. 3. Survival of the Fittest The more fit and organism is for the environment it lives in, the better it’s fitness or survival

DARWIN’S THEORY AND THE MODERN SYNTHESIS  Darwin also saw that humans choose organisms with specific characteristics Breeding organisms with specific traits in order to produce offspring with identical traits is called artificial selection.  Darwin hypothesized that there was a force in nature that worked like artificial selection.

Natural selection - the mechanism of evolution  Darwin hypothesized that there was a force in nature that worked like artificial selection.  Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted As a result, the proportion of individuals with favorable characteristics increases Populations gradually change in response to the environment  Organisms without these variations are less likely to survive and reproduce.

Darwin explains natural selection  In nature, organisms produce more offspring than can survive.

 In any population, individuals have variations. Fishes, for example, may differ in color, size, and speed.

 Individuals with certain useful variations, such as speed, survive in their environment, passing those variations to the next generation.

 Over time, offspring with certain variations make up most of the population and may look entirely different from their ancestors.

Structural adaptations arise over time  The ancestors of today’s common mole-rats probably resembled African rock rats.

Structural adaptations arise over time  Some ancestral rats may have avoided predators better than others because of variations such as the size of teeth and claws.

Structural adaptations arise over time  Ancestral rats that survived passed their variations to offspring.  After many generations, most of the population’s individuals would have these adaptations.

Structural adaptations arise over time  Over time, natural selection produced modern mole-rats.  Their blindness may have evolved because vision had no survival advantage for them.

Structural adaptations arise over time  Mimicry is a structural adaptation that enables one species to resemble another species.  Predators may learn quickly to avoid any organism with their general appearance

Structural adaptations arise over time  camouflage, an adaptation that enables species to blend with their surroundings.  Because well- camouflaged organisms are not easily found by predators, they survive to reproduce.

 In general, most structural adaptations develop over millions of years.  However, there are some adaptations that evolve much more rapidly.  The evolution of insecticide resistance is an example of natural selection in action Rapid Adaptations

Evidence for Evolution  Physiological resistance in species of bacteria, insects, and plants is direct evidence of evolution.  Biogeography Closely related but different Distantly related but similar (wolves and dogs)

Evidence for Evolution Fossils  provide a record of early life and evolutionary history.  Although the fossil record provides evidence that evolution occurred, the record is incomplete  As the fossil record becomes more complete, the sequences of evolution become clearer

Comparative anatomy Homologous structures: Structural features with a common evolutionary origin Can be similar in arrangement, in function, or in both

Comparative anatomy Analogous Structures :  The body parts of organisms that do not have a common evolutionary origin but are similar in function  Although analogous structures don’t shed light on evolutionary relationships, they do provide evidence of evolution  For example, insect and bird wings probably evolved separately when their different ancestors adapted independently to similar ways of life.

Comparative Anatomy Vestigial Structure  a body structure in a present-day organism that no longer serves its original purpose, but was probably useful to an ancestor.  Vestigial structures, such as pelvic bones in the baleen whale, are evidence of evolution because they show structural change over time.

Comparative Embryology  developmental patterns are similar in organisms with similar evolutionary relationships  The embryos of a fish, a reptile, a bird, and a mammal have a tail and pharyngeal pouches.

Comparative Biochemistry  Nearly all organisms share DNA, ATP, and many enzymes among their biochemical molecules.  biologists use RNA and DNA nucleotide sequences to construct evolutionary diagrams.  Organisms that are biochemically similar have fewer differences in their amino acid sequences.

Chapter 17 Evolution of Populations

Populations, not individuals, evolve If an organism has a feature—called a phenotype in genetic terms—that is poorly adapted to its environment, the organism may be unable to survive and reproduce.

Populations, not individuals, evolve Natural selection acts on the range of phenotypes in a population. Picture all of the alleles of the population’s genes as being together in a large pool called a gene pool. The percentage of any specific allele in the gene pool is called the allelic frequency. Any factor that affects the genes in the gene pool can change allelic frequencies, which results in the process of evolution.

Mechanisms for genetic change  1. Mutation occasionally, a mutation results in a useful variation, and the new gene becomes part of the population’s gene pool by the process of natural selection.  2. genetic drift the alteration of allelic frequencies by chance events.

Natural selection acts on variations There are three different types of natural selection that act on variation: stabilizing, directional, and disruptive.

Stabilizing Selection a natural selection that favors average individuals in a population. Selection for average size spiders Normal variation

Directional Selection occurs when natural selection favors one of the extreme variations of a trait. Normal variation

Disruptive Selection individuals with either extreme of a trait’s variation are selected for. Selection for light limpets Normal variationSelection for dark limpets

Genetic Drift  In small populations, individuals that carry a particular allele may leave more descendants than other individuals leave, just by chance.  Over time, a series of chance occurrences can cause an allele to become more or less common in a population  This is called GENETIC DRIFT

Genetic Bottlenecks  A change in allele frequency following a dramatic reduction of the population size.  Can greatly reduce a population’s genetic diversity.

The Founder Effect  Allele Frequencies change as a result of the migration of a small subgroup of a population.

Genetic Equilibrium  population is not evolving, the allele frequencies in the gene pool do not change.

Hardy-Weinberg Principle  Predicts 5 conditions that disrupt genetic equilibrium and cause evolution to occur. 1. Nonrandom Mating 2. Small Population Size 3. Immigration or Emigration (introducing new genes to the gene pool or removing them) 4. Mutations 5. Natural Selections

The Evolution of Species Significant changes in the gene pool could lead to the evolution of a new species over time. The evolution of new species, a process called speciation occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment.

Isolating Mechanisms  Geographic isolation ○ A new species can evolve when a population has been geographically isolated.  Behavioral Isolation ○ Two populations that are capable of interbreeding develop differences in courtship rituals and other behaviors.  Reproductive Isolation ○ Populations become reproductively isolated when they evolve into two separate species  Temporal Isolation ○ When two or more species reproduce at different times