Evolution

• Definitions:

• “genetic change in a population”

• “change in gene frequencies within the gene pool”

I. Historical Background

A. Georges Cuvier (1769-1832)--catastrophism and paleontology

B. James Hutton (1795)--gradualism

C. Jean Baptiste Lamarck (1809)

1. Innate tendency toward perfection

2. Use and disuse = Use an organ and it develops; do not use it and it deteriorates.

3. Inheritance of acquired characteristics

http://thinks.com/puzzles/hidden1.htm

D. Charles Darwin (1809-1882)

1. Major influences

a. Voyage of the HMS Beagle (1831-1836)

b. Charles Lyell , friend, wrote Principles of Geology (1830) (uniformitarianism)

c. Thomas Malthus, “Essay on the Principles of Population” (1797) --geometric

population increases are countered by environment factors i.e. starvation, war, disease

d. artificial selection--pigeons, dogs, roses

2. Mechanism of natural selection

a. Variation exists among all living things.

b. There is an overproduction of offspring. (exponential growth)

c. This leads to competition for resources and space.

d. Those best adapted to the environment due to their genetic makeup survive and reproduce, passing on their favorable adaptations.

II. The Evidence of EvolutionA. Paleontology--fossil studies

1. Types of fossils--petrified copies, carbon copies, casts, footprints, amber

2. Fossil series – bones of ancestors are put in a sequence – Example: horses

(danger of oversimplification here)

3. Index fossils are used to correlate rock strata and organize geological column

An Ammonite. By permission of Emporia State University Geology Museum, Emporia, KS.

B. Comparative anatomy

1. Homologous structures, i.e. features that are similar based upon structure, these similarities indicate common ancestry.

2. Analogous structures, i.e. features that similar based upon function, these similarities do not indicate common ancestry

C. Vestigial Structures – structures with no current known functions

-human ear muscles, wisdom teeth, body hair, limb bones in pythons and whales

D. Embryology - closely related organisms go through similar development stages as embryos

E. Biogeography (geographical distribution)1. Australia2. Galapagos Islands3. Hawaiian Islands

F. Biochemistry1. Amino acid sequences - cytochrome c2. Nucleotide sequences in DNA – cytochrome b

G. Microevolution – change within a species that has not yet led to species formation1. Insecticides and insects2. Antibiotics and pathogenic bacteria3. Finch’s beak

Play Game

III. Speciation (Chapter 19)

A. Definition of species

1. Group of organisms with a common gene pool

2. Group characterized by reproductive isolation (gene pool is isolated)

3. Group sharing morphological similarities

B. Reproductive Barriers -- restrict gene flow, but are not geographical

1. Prezygotic barriers

2. Postzygotic barriers -- usually chromosomal problems

C. Speciation -- when two populations of a species become so different that there is no gene flow between them when they are brought together, i.e. they demonstrate reproductive isolation

1. Allopatric speciation -- caused by geographical separation

a. Galapagos Islands -- small isolated groups form, genetic drift (founder effect) in action

b. Barrier formation -- rivers, mountains, glaciers, land slides, etc., gene flow is interrupted, different habitats are sometimes formed, usual result is extinction

What is Phylogeny?Biologists estimate that there are about 5 to 100 million species of organisms living on Earth today. Evidence from morphological, biochemical, and gene sequence data suggests that all organisms on Earth are genetically related, and the genealogical relationships of living things can be represented by a vast evolutionary tree, the Tree of Life. The Tree of Life then represents the phylogeny of organisms, i. e., the history of organismal lineages as they change through time. It implies that different species arise from previous forms via descent, and that all organisms, from the smallest microbe to the largest plants and vertebrates, are connected by the passage of genes along the branches of the phylogenetic tree that links all of Life (Figure 1).

                                                                                                     

Figure 1: All organisms are connected by the passage of genes along the branches of the phylogenetic Tree of Life.

The organisms that are alive today are but the leaves of this giant tree, and if we could trace their history back down the branches of the Tree of Life, we would encounter their ancestors, which lived thousands or millions or hundreds of millions of years ago (Figure 2).

From: http://tolweb.org/tree/learn/concepts/whatisphylogeny.html

                                                                                                                          Figure 2: Living organisms sit like leaves at the tips of the branches of the Tree of Life. Their evolutionary history is represented by a series of ancestors which are shared hierarchically by different subsets of the organisms that are alive today.

The notion that all of life is genetically connected via a vast phylogenetic tree is one of the most romantic notions to come out of science. How wonderful to think of the common ancestor of humans and beetles. This organism most likely was some kind of a worm. At some point this ancestral worm species divided into two separate worm species, which then divided again and again, each division (or speciation) resulting in new, independently evolving lineages. Little did these worms know, those hundreds of million years ago, that some of their number would end up evolving into beetles, while their brothers and sisters would end up as humans or giraffes.Organisms have evolved through the ages from ancestral forms into more derived forms. New lineages generally retain many of their ancestral features, which are then gradually modified and supplemented with novel traits that help them to better adjust to the environment they live in. Studying the phylogeny of organisms can help us explain similarities and differences among plants, animals, and microorganisms. The Tree of Life thus provides a rigorous framework to guide research in all biological subdisciplines, and it is therefore an ideal model for the organization of biological knowledge.

2. Sympatric speciation -- new species within same geographical area as parent species (common in plants, rare in animals)

[polyploidy = 2n 4n]

a. Autopolyploidy -- self-fertilizing plant become tetraploid, thus cannot interbreed with parents

b. Allopolyploidy -- a new species forms from a normally sterile hybrid

V. Patterns of speciation

A. Anagenesis -- phyletic evolution1. transformation of a single ancestral

species into a single descendant species

B. Cladogenesis -- branching evolution1. transformation of one ancestral species

into more than one descendant species

2. a type of speciation

C. Adaptive radiation

D. Convergent Evolution

VI. Pace of EvolutionA. Gradualism (Darwin) -- change occurs

stepwise or gradually

-no stasis

-many intermediate forms

B. Punctuated equilibrium (Stanley, Gould)

-rapid change, then stasis

-few transitional forms

[Fossil record manifests repeated mass extinctions followed by mass speciation. (26 million year cycle)]