Thinking About Darwinian Thinking About Darwinian Evolution:Evolution:

What is evolution?? And what is this finch doing?!?

We owe much of our understanding of EVOLUTION to

CHARLES CHARLES DARWINDARWIN..

Darwin’s Origin of Species (1859):

1. Descent with Modification (Evolution)

2. Natural Selection as a mode of Evolution

Remember: Mendel publishes in 1866…

Darwin’s Natural Selection:Darwin’s Natural Selection:

Observation #1: Individual Variation

Observation #2: Struggle for Existence

Inference: Differential Reproductive Success or Natural Selection

ADAPTATIONSADAPTATIONS are the result of natural selection.

Darwin also proposed that natural selection, over time, could

produce new species from ancestral species.

This was his explanation for the 14

unique species of finches he

observed on the

Galapagos Islands.

Darwin’s Historical Context: The Philosophy of the Time

•Plato (427-347 BC): two worlds: a real (ideal) world, and an illusory world (imperfect) that we perceive with our senses.

•Aristotle (384-322 BC): all living forms can be arranged on a scale or ladder or increasing complexity. (All rungs taken!)

•Judeo-Christian Context: Biology in Europe and America dominated by natural theology- classifying species in order to reveal the steps of the scale of life God created.

The Historical ContextThe Historical Context"Those who which to succeed must ask the right preliminary questions." - Aristotle

FOSSILS: Paleontology (the study of fossils) is developed by Cuvier (1769-1832). He documents the succession of fossil species in the Paris Basin. He advocates catastrophism rather than evolution.

Darwin’s Historical Context: The Philosophy of the Time

GEOLOGICAL THEORIES: Hutton (1726-1797) proposes gradualism (profound change is the result of

slow continuous processes). Lyell (1797-

1875) expands to uniformitarianism

(geologic processes have not changed throughout the Earth’s long history).

Darwin’s Historical Context: The Philosophy of the Time

Other Scientists had suggested EVOLUTION, but none had proposed a MECHANISM!

First Mechanism: Jean Baptiste Lamarck

Lamarck observes several lines of descent in fossils. Suggests that use and disuse results in change in morphology. He

suggests that these acquired characteristics (adaptations!)

could be inherited.

This is wrong, but visionary!

Malthus contends Malthus contends that much of that much of

human suffering is human suffering is the unavoidable the unavoidable

consequence of the consequence of the potential for the potential for the

human population human population to increase faster to increase faster than food supplies than food supplies

and other and other resources.resources.

Darwin is heavily influenced by Darwin is heavily influenced by Thomas Thomas MalthusMalthus’ writings on ’ writings on

human population (1798)human population (1798)

Darwin’s MECHANISM = NATURAL SELECTION

•Natural selection is differential success in reproduction

•Natural selection occurs through an interaction between the environment and the variability inherent among the individual organisms making up a population

•The product of natural selection is the adaptation of populations of organisms to their environment.

Darwin’s ideas remain

unpublished until another scientist, Alfred Wallace, independently develops the

same theory of Natural

Selection.

Darwin publishes second, but in

much more detail.

Darwin illustrates his mechanism with examples from ARTIFICIAL

SELECTION, the breeding of domesticated plants and animals

If artificial selection can change so much in a relatively short time, argues Darwin, then

natural selection should be capable of considerable modifications.

Examples of Natural Selection:

•Insecticide-Resistant Insects

•Antibiotic-Resistant Bacteria

•Drug-Resistance in HIV

Other Evidence of Evolution: HomologyHomology

Similarity in characteristics resulting from common ancestry is known as

HOMOLOGY.

Homology can be:

1. Anatomical (Homologous Structures)

2. Molecular (esp. DNA)

3. Embryological- developmental structures and processes.

Anatomical Homology:Anatomical Homology:

FISH

REPTILEFISH CHICKEN HUMAN

Developmental Developmental Homology:Homology:

MOLECULAMOLECULAR R HOMOLOGYHOMOLOGY::

Some HOMOLOGIES are MISLEADING…Some HOMOLOGIES are MISLEADING…

as they result from as they result from CONVERGENT CONVERGENT EVOLUTIONEVOLUTION..

BIOGEOGRAPHYBIOGEOGRAPHY, or the geographic distribution of species, provides many

clues about their evolution.

Islands are especially good for studying biogeography as they contain many isolated, endemic

species.

The The FOSSIL RECORDFOSSIL RECORD provides the last major provides the last major line of evidence in support of Darwin’s ideas.line of evidence in support of Darwin’s ideas.

The Darwinian view of life predicts the existence of evolutionary transitions.

Bailosaurus

Thus Darwin’s views are supported by multiple, independent lines of

evidence.

Evolutionary patterns of HomologyHomology that match patterns in space

(BiogeographyBiogeography) and time (the Fossil Fossil RecordRecord).