Chapter 22~ Descent with Modification: A Darwinian View of Life

Evolution

Evolution : the change over time of the genetic composition of populations

Natural selection : populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success)

Evolutionary adaptations : a prevalence of inherited characteristics that enhance organisms’ survival and reproduction

Evolutionary history

Historical Context for Evolution

Plato: [427-347 B.C.] 2 worlds

Real world, ideal, eternal

Perceived world, seen via senses

Aristotle: [384-322 B.C.] scala naturnae

Living forms arranged on a scale (ladder)

Each form had a rung, all rungs occupied

1700’s: natural theology

Adaptations were designs of the Creator

Historical Context for Darwin

Linnaeus : taxonomy (classification of organisms based on enduring traits), binomial nomenclature

Hutton : gradualism; changes in earth due to slow, continuous changes accumulating

Lamarck : evolution; inheritance of acquired traits, use and disuse

Malthus : populations overproduce, catastrophes the result of human population increasing faster than supplies

Cuvier : paleontology, succession of fossils in strata of sediments, change due to catastrophism (local)

Historical Context for Darwin

Lyell : uniformitarianism, consistent change over time (rate of gradualism is constant

Darwin : evolution via natural selection

Mendel : inheritance of traits from parent to offspring

Wallace : evolution by natural selection, published first, less evidence than Darwin

Descent with Modification, I

5 observations :

1- Exponential fertility

2- Stable population size

3- Limited resources

4- Individuals vary

5- Heritable variation

Descent with Modification, II

3 Inferences :

1- Struggle for existence

2- Non-random survival

3- Natural selection (differential success in reproduction)

DARWIN SUMMARY

Natural selection is differential success in reproduction

Natural selection occurs through an interaction between the environment and the variability inherent among individuals in a population

The product (result) of natural selection is the adaptations of organisms to their environment.

REMEMBER:

Individuals are selected;

populations evolve.

Evolution evidence: Biogeography

Geographical distribution of species

Examples: Islands vs. Mainland Australia Continents

Evolution evidence: The Fossil Record

Succession of forms over time

Transitional links

Vertebrate descent

Evolution evidence: Comparative Anatomy

Homologous structures (homology)

Descent from a common ancestor

Vestigial organs Ex: whale/snake hindlimbs; wings on flightless birds

Analogous structures: evidence of change

Evolution evidence: Comparative Embryology

Pharyngeal pouches, ‘tails’ as embryos

Patterns of similarity in closely related species

Evolution evidence: Molecular Biology

Similarities in DNA, proteins, genes, and gene products

Common genetic code

Same amino acids

Final words…...

“Absence of evidence is not evidence of absence.”