|AP Biology Lecture Ch. 22
Descent with Modification: A Darwinian View of Life
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
They leave more offspring than others (differential reproductive success)
Evolutionary adaptations: a prevalence of inherited characteristics that enhance organisms’ survival and reproduction
Historical Context for Evolutionary Theory
Aristotle-all species can be arranged on a ladder of increasing complexity. Species are permanent and do not evolve. Humans at the top of the ladder.
Carolus Linnaeus-specialized in taxonomy.
Developed naming system-binomial nomenclature.
genus and a species
characterized by different fossils.
Thought catastrophes were responsible for the changes. Strong opponent against evolution.
James Hutton-gradualism -Forces he saw today, water, wind, ice, were the same “The present is a key to the past.”
Lyell- Uniformitarianism - geologic change results from slow, continuous actions. Believed earth was much older than 6,000 yrs.
Lamarck- Theory of acquired traits and theory of use and disuse. He stated that Individual organisms change in response to their environment.
Wallace-published an essay identical to Darwin’s.
Darwin- theory of natural selection Published “On the Origin of the Species” in 1859 - spurred on by appearance of Wallace’s essay.
Linnaeus: taxonomy Lyell: uniformitarianism Wallace: evolution
Hutton: gradualism Cuvier: paleontology
Lamarck: evolution Darwin: evolution
Malthus: populations Mendel: inheritance
Descent with Modification
1- Exponential fertility
2- Stable population size
3- Limited resources
4- Individuals vary
5- Heritable variation
1- Struggle for existence
2- Non-random survival
3- Natural selection (differential success in reproduction)
Darwin’s theory of natural selection
Overpopulation-populations grow exponentially and exceed their resources.
Overpopulation results in competition and a struggle for existence.
Reaches a stable population
Variation in population
Best-Fit individuals survive and pass their traits on to their offspring.
Evolution occurs as advantageous traits accumulate in a population.
Evidence for Evolution
Biogeography-geographic distribution of species. First suggested by Darwin
Species tend to be more closely related to other species from the same area than to other species with the same way of life but living in different areas.
Fossil record-shows the existence of species that have become extinct or have evolved
into other species. Earth is about 4.6 billon years old.
Prokaryotes first organisms to develop on earth and oldest fossils.
Comparative anatomy-study of different structures help scientists understand the
evolution of anatomical structures and of evolutionary relationships.
Homologous structures-have a common origin and reflect a common ancestry.
Forelimbs of humans, cats, whales, bats all similar due to a common ancestry.
Analogous structures-different structure, same function. Bat’s wing and a fly’s wing.
It reflects an adaptation to similar environments, not descent from a recent common ancestor.
Vestigial structures-evidence that structures have evolved. Homologous structures that
don’t really have any function in the organism any more.
Comparative embryology-closely related organisms go through similar stages in their
Molecular Biology-similar DNA, protein, genes, gene products.
Geographical distribution of species
Examples: Islands vs. Mainland
The Fossil Record
Succession of forms over time
Homologous structures (homology)
Descent from a common ancestor
Vestigial organs Ex: whale/snake hind limbs;
wings on flightless birds
tails’ as embryos
Similarities in DNA, proteins, genes, and gene products
Common genetic code