BSC 1010 Lecture 18: CHAPTER 21,22,23 Notes

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Florida International University
Biological Science
BSC 1010
John Geiger

3 conditions of natural selection (modern evidence for Darwin's hypothesis) 1. Variation must exist in the population 2. Variation must lead to differences in reproductive success 3. Variation must be genetically transmitted to the next generation directional Artificial selection is a form of _______ selection that leads to evolutionary change Vestigial structures have no apparent function, but resemble structures their ancestors possessed. e.g. hip bones in whales, human ear wiggling muscles Convergent evolution Similar forms having evolved in different, isolated areas because of similar selective pressures in similar environments. e.g. Australian marsupials resemble placental mammals on other continents. Arguments against Darwin's theories (and reasons why they are in wrong) -Evolution is not solidly demonstrated (it is a theory just like the theory of gravity) -There are no fossil intermediates (many have been found since Darwin's time) -The intelligent design argument (too complex for a random process, natural selection is not random but it is not directed) -Evolution violates the Second Law of Thermodynamics (Earth is not a closed system and energy is constantly added from the sun) -Proteins are too improbable -Natural selection does not imply evolution -The irreducible complexity argument Sympatric species occur together in an area. Distinctive, phenotypically different, utilize different parts of the habitat, behave separately Ernst Mayr defined species as groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups Subspecies Within a single species, individuals in populations that occur in different areas may be distinct from one another. Prezygotic isolating mechanisms Geographic isolation, ecological isolation, behavioral isolation, temporal isolation, mechanical isolation, prevention of gamete fusion. Postzygotic isolating mechanisms hybrid inviability or infertility Cladogenesis One ancestral species becomes divided into two descendant species Genetic drift random changes may cause reproductive isolation. In small populations, Founder effects, bottleneck effects Speciation is a 2-part process 1. Initially identical populations must diverge. 2. Reproductive isolation must evolve to maintain these differences. Allopatric speciation Geographically separated populations appear much more likely to have evolved substantial differences leading to speciation. Sympatric speciation One species splits into two at a single locality, without the two new species ever having been geographically separated. One type occurs commonly as a result of polyploidy (individuals that have more than two sets of chromosomes) Autoploidy all the chromosomes arise from a single species, error in cell division produces tetraploids, cannot produce fertile offspring with normal diploids Allopolyploidy Two species hybridize, resulting offspring have one copy of the chromosomes of each species. Infertile, but can reproduce asexually. Can become fertile if chromosomes spontaneously doubled (polyploidy) Adaptive radiation Occurs in an environment with few other species and many resources. New trait evolves within a species allowing it to use resources that were previously inaccessible. Island archipelago example Gradualism The model that assumes that evolution proceeds with accumulation of small changes Punctuated equilibrium Long periods of stasis followed by rapid change. Stabilizing and oscillating selection is responsible for stasis. ends of a continuum Gradualism and punctuated equilibrium are two _________ Systematics the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic trees, phylogenies) "Descent with modification" Darwin - all species evolved from a single common ancestor, history of life as a branching tree Phylogeny Hypothesis about patterns of relationships among species. Monophyletic group includes the most recent common ancestor of the group and all of its descendants (clade) Paraphyletic group includes the most recent common ancestor of the group, but NOT all of its descendants. Polyphyletic group does not include the most recent common ancestor of all members of the group postzygotic A type of isolating mechanism that leads to reproductive isola
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