Ap biology Lecture Ch. 22 Descent with Modification: a darwinian View of Life

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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.

Evolutionary history
Linnaeus: taxonomy Lyell: uniformitarianism Wallace: evolution
Hutton: gradualism Cuvier: paleontology
Lamarck: evolution Darwin: evolution
Malthus: populations Mendel: inheritance

Descent with Modification
5 observations:
1- Exponential fertility
2- Stable population size
3- Limited resources
4- Individuals vary
5- Heritable variation
3 Inferences:
1- Struggle for existence
2- Non-random survival
3- Natural selection (differential success in reproduction)
Darwin’s theory of natural selection

  1. Overpopulation-populations grow exponentially and exceed their resources.

  1. Overpopulation results in competition and a struggle for existence.

  1. Reaches a stable population

  1. Variation in population

  1. Best-Fit individuals survive and pass their traits on to their offspring.

  1. 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

embryonic development.

Molecular Biology-similar DNA, protein, genes, gene products.
Evolution evidence:


Geographical distribution of species

Examples: Islands vs. Mainland

The Fossil Record

Succession of forms over time

Transitional links

Vertebrate descent

Comparative Anatomy

Homologous structures (homology)

Descent from a common ancestor

Vestigial organs Ex: whale/snake hind limbs;

wings on flightless birds

Comparative Embryology

Pharyngeal pouches‘

tails’ as embryos
Molecular Biology

Similarities in DNA, proteins, genes, and gene products

Common genetic code

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