Office: LSci 315
Office hours: M F 12:00-1:00 pm

Course website:
access through Biology website
or through http://www.d.umn.edu/~arachins

How does one succeed in the 2nd half:
- attend lectures & take notes
- responsible for what’s covered in lecture
- transcribe notes
- read text
- re-write notes & re-read text
- use study guide
- review, word roots, questions
- study groups

CHAPTER 22
DESCENT WITH MODIFICATION:
A DARWINIAN VIEW OF LIFE
Lecture Outline
• Historical Context for Evolutionary Theory
• Early players
• Influence of paleontology & geology
• The Darwinian Revolution
• The voyage of the Beagle
• Evidence for Darwin’s hypotheses of evolution and natural selection

Theory of evolution
• Charles Darwin 1859
‘On the Origin of Species by Means of Natural Selection’
- synthesis of seemingly unrelated facts
- biological questions
- two major points:
• Species evolved from ancestral species
• Natural selection

What is a ‘theory’ ?
• Darwin’s ‘ theory of natural selection’
• theory in colloquial use: closer to the concept of a “hypothesis” in science
• in science, a theory is more comprehensive than a hypothesis
- accounts for many facts
- attempts to explain a great variety of phenomena
Example: Newton’s theory of gravitation

Classical Greek Philosophers Influenced Western Culture

• Plato (427-347 B.C.): one perfect real world and an illusory world of imperfection

• Aristotle (384-322 B.C.): all living forms could be arranged on a ladder (scala naturae) of increasing complexity

- perfect, permanent species.

Common views in the 18th & 19th century
• Earth only a few thousand years old
• Creator made life in a week
• Unchanging life forms
• Natural theology:
- adaptations of organisms as evidence that the Creator had designed each species for a purpose
• Carolus Linnaeus (1707-1778) develops taxonomy:
- binominal nomenclature
- Genus species (Apis mellifera)
- hierarchy of increasingly complex categories
- did not imply evolutionary relationship

Historical context of Darwin’s life and ideas

Paleontology influenced Darwin
• the study of fossils
• succession of fossil species in strata of sedimentary rock:

• Cuvier (1769-1832):
• extinction common occurrence
• catastrophism
• repopulation

Fossils in an evolutionary context
• Jean Baptiste Lamarck (1744-1829)
• identified several lines of descent
in collected fossils and current species
• chronological series of older to younger fossils leading to a modern species
• ‘use & disuse’ ? inheritable acquired characteristics
= wrong
• Credit for visionary aspects of his theory:
- great age of earth
- evolution explains fossil record & current diversity
- evolution ? adaptation

Influenced by geology
• James Hutton (1726-1797):
• diversity of land forms
could be explained by
mechanisms currently operating
• gradualism ? profound change results from slow, continuous processes
• Charles Lyell (1797-1875):
• uniformitarianism ? geological processes had not changed throughout Earth’s history
- earth must be much older than 6000 years
- slow and subtle changes lead to substantial change

CHAPTER 22
DESCENT WITH MODIFICATION:
A DARWINIAN VIEW OF LIFE
Lecture Outline
• Historical Context for Evolutionary Theory
• Early players
• Influence of paleontology & geology
• The Darwinian Revolution
• The voyage of the Beagle
• Evidence for Darwin’s hypotheses of evolution and natural selection

The Darwinian Revolution

Field research helped Darwin frame his view of life
• Darwin collected thousands of specimens of the diverse flora and fauna of South America
• South American flora & fauna different from Europe
• Species from SA tropical and temperate regions similar
• SA fossils distinctive

Fauna of Galapagos
• Many unique animal species:
• 14 finch species
• some on a single island
• Fauna similar to mainland
• Islands colonized by plants and animals from the mainland that had then diversified on the different islands.

Darwinism
- Evolution as explanation for the diversity of life
- theory of natural selection as the mechanism for adaptive evolution

• 1844: Darwin’s essay on the origin of species and natural selection
• 1858: Alfred Wallace’s theory of natural selection
• 1859: Darwin’s The Origin of Species published

Natural selection and adaptation
• Ernst Mayr (evolutionary biologist):

• Observation #1: High fertility leads
to exponential population growth.
• Observation #2: Populations tend
to remain stable in size
• Observation #3: Environmental
resources are limited.

• Inference #1: Production of more individuals than the environment can support leads to a struggle for existence among the individuals of a population, with only a fraction of the offspring surviving each generation.

• Observation #4: Individuals of a population vary extensively in their characteristics.
• Observation #5: Much of this variation is heritable.

• Inference #2: Survival is not random, but depends in part on the heredity ? i.e. transfer of traits from parents to offspring.
• Inference #3: Given the limited resources, individuals have varying abilities to survive ? only the most fit individuals will survive and reproduce ? gradual change in a population.

Summary and review of Darwin’s ideas
• Natural selection is differential success in reproduction (unequal ability of individuals to survive and reproduce).
• Natural selection occurs through an interaction between the environment and the variability among individuals within a population.
• The product of natural selection is the adaptation of populations of organisms to their environment.

Artificial selection
• Agricultural plants & domestic animals
• Modification over just a few generations
• Little resemblance to wild ancestors

Darwin’s view on artificial selection
• If artificial selection can achieve major changes in a relatively short time, then natural selection should be capable of major modifications of species over hundreds or thousands of generations.
• Darwin envisioned the diversity of life as evolving by a gradual accumulation of minute changes through the actions of natural selection operating over vast spans of time.

Populations evolve
• Population
- group of interbreeding individuals
- of one species
- sharing common geographic area
• Natural selection
- involves interactions between individuals and their environment
- amplifies or diminishes heritable variations

- change in heritable variation in a population
occurs over a succession of generations
- populations evolve, not individuals

Natural selection in action: Insecticide-resistance
• Natural selection edits existing variation.
• Natural selection favors advantageous characteristics.

Natural selection in action: drug-resistant HIV
• Natural selection favors drug-resistant virus strains
• 3TC-resistant strains become 100% of the population of HIV in just a few weeks

Evidence of evolution : homologous structures
• anatomical similarities between species grouped in the same taxonomic category
• Example: forelimbs of tetrapods

- homologous
structures

Evidence of evolution: vestigial organs
• Humans have muscles to move their ears
• Humans have a vestigial tailbone
• Vestigial toes in the horse
• Vestigial limbs in snakes
and whales

Evidence of evolution : embryological homologies
• all vertebrates have pharyngeal pouches

- gills of fish
- Eustachian tube in mammals

Evidence of evolution :
molecular homologies
• Genetic code
- shared by all life
= ancient

• Protein similarities
- shared by related species
= evolved more recently

Evidence of evolution : biogeography
• anatomical similarities between unrelated species

- different mammalian ‘brands’ in different geographic regions
- resemblance is an example for convergent evolution

Evidence of evolution : island flora & fauna
• endemic species: found nowhere else
• related species evolved from common ancestor

Evidence of evolution : the ‘missing link’
• evolutionary transitions leave signs in fossil record

The ‘Origin of Species’ 1859
• diversity of life is attributed to natural causes rather than to supernatural creation,
- Darwin gave biology a sound, scientific basis

• As Darwin said,
“There is grandeur
in this view of life.”

Key Terms 22
natural selection
descent with modification
evolutionary adaptation
artificial selection
natural theology
homology
taxonomy
homologous structures
fossil
vestigial organs
paleontology
biogeography
sedimentary rock
endemic
catastrophism
gradualism
uniformitarianism