Chapter 16 The Theory of Evolution

What You’ll LearnWhat 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 changingHe concluded that living things also change,

or evolve over generationsHe also stated that living species descended

from earlier life-forms: descent with modification

Darwin’s Ideas1. 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.

BiogeographyClosely related but different Distantly related but similar (wolves and dogs)

Evidence for EvolutionFossils

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 anatomyAnalogous 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 AnatomyVestigial 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. Mutationoccasionally, 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 variation Selection 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 Mating2. Small Population Size3. Immigration or Emigration (introducing new

genes to the gene pool or removing them)4. Mutations5. 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