Chapter 22 Notes

Descent with Modification: A

Darwinian View of Life

Darwin made two points in The Origin of Species.- the species on the earth today descended from ancestral species- the mechanism for evolution is natural selection

Natural Selection: populations can change over time if individuals with certain traits have more offspring than other individuals

The result of natural selection is evolution- the genetic composition of a population changes over time.

Western culture resisted evolutionary views of life

In the 1700’s, biology in Europe and America was dominated by natural theology- dedicated to discovering the Creator’s plan for studying nature

Carolus Linnaeus sought to discover order in the diversity of life.- specialized in taxonomy: branch of biology that focuses on naming and classifying the diverse forms of life- his system of taxonomy became a focal point in Darwin’s arguments for evolution

The study of fossils also helped lay the groundwork for Darwin’s ideas.

Fossils: impressions from the past found in sedimentary rocks formed from the sand and rocks of seas and lakes

Gradualism helped paved the way for evolution

James Hutton: explained geologic features through gradualism- change is the cumulative product of a slow but continuous process

Charles Lyell: incorporated gradualism into uniformitarianism- geologic change occurs at a constant rate

Lamarck placed fossils in an evolutionary context

Jean Baptiste Lamarck: published his theory of evolution in 1809

Remembered for his mechanism of evolution- first idea was use and disuse- second was inheritance of acquired characteristics

Darwin study of evolution first began as a naturalist on the HMS Beagle- travel around the world observing and documenting the types of plants and animals at the various locations- he did not understand the scope of the findings until after returning to England

Darwin chose not to publish his findings until prompted by Alfred Walace in 1858

The next year Darwin published The Origin of Species

The Origin of Species developed two main points

Descent with Modification:- as populations spilled into new environments, modifications become prominent over time- helped fit organisms into ways of life

Natural Selection:- nature chose what features are beneficial and give an increased chance of survival

The history of life is like a tree.- each fork of the tree is an ancestor who is common to others from that fork

Summary of Darwin’s main ideas-Natural selection is differential success in

reproduction-Occurs through an interaction between the

environment and the variability inherent among the individual organisms making up a population

The product of N.S. is the adaptation of populations to their environment.

Connection between N.S., the struggle for existence, and the capacity of organisms to “overreproduce.”- Thomas Malthus (1798)

Artificial selection: the breeding of domesticated plants and animals

N.S occurs between individuals and the environment, but only populations (not individuals) evolve.

N.S. can amplify or diminish only heritable variations (not acquired characteristics)

Evidence of N.S. provides evidence for evolution

Insecticide-Resistant Insects- natural selection causes the evolution of resistance to insecticides

- only a few insects are resistant to the first wave insecticide

- those reproduce and pass on the gene to the second generation

- eventually the whole population will be resistant- Drug-resistant HIV

Homology: similarity of characteristics resulting from common ancestry

Anatomical Homologies- the forelimbs of mammals have the same skeletal structures (homologous structures)

- vestigial structures: structures of marginal, if any, importance to the organism

-ex. pelvis and leg bones of snakesEmbryological Homologies

- all vertebrate embryos have pharyngeal pouches some time in their development.

Molecular Homologies: all species of life use the same machinery of DNA and RNA- the more similar the animals, the more similar the genetic material

Biogeography: the geographic distribution of species- first suggested evolution to Darwin- species tend to be more closely related to others from the same area than to others with the same way of life, but from other areas

- ex. sugar glider (of Australia)

Islands often have a large amount of biodiversity

They have many endemic species found nowhere else in the world

Small changes can be seen in an island chain or archipelago

The Fossil RecordThe succession of fossil forms is compatible

with other types of evidence for evolution- ex. prokaryote fossils are older than eukaryote fossils- ex. fish fossils, amphibians, reptiles, mammals and birds

Many fossils link older fossils with modern species.- ex. change in skull shape and size