BIOL 1001 Chapter 3: Chapter 3.3.docx
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Evolution: gradual change in the characteristics of a population of organisms over time (can be the result of selection)
ch 17 / 18 / 19 / 20
Theory of Evolution: explains both the unity and diversity of life organisms alive today descended from a common ancestor
Common ATP DNA and plasma membrane
species change over time as a result of natural selection
Central ideas of Darwin’s theory of evolution by natural selection summarized:
individual organisms in a population vary in many heritable traits
any population has the potential to produce far more offspring than the environment can support. competition for limited
resources means that only some individuals survive
some individuals in the population have traits that give them an advantage in their local environment; these organisms are
likely to survive and reproduce.
these organisms pass on favourable traits to their offspring. Over time, the incidence of the trait(s) will change in
organisms diverged over evolutionary time in response to selection pressures of different environments
adaptive radiation example of divergence
3.3a Adaptive Radiation: Diversification of Lineages of Life
development of photosynthesis example of an organism overcoming a fundamental barrier that was crossed and opened new
opportunities for diversification.
appearance of oxygenic photosynthesis increased concentrations of O2 which led to aerobic respiration and the ozone layer.
-ozone layer: allowed organisms to colonize by blocking harmful UV rays.
paleontological evidence of relative timing of some fundamental changes in life
-eg. evolution of whales
-sometimes know the underlying factors
organism move into new adaptive zone after chance innovation allows use of environment in unique way.
examples: -plants move onto land (new opportunities for animals)
-dehydration-resistant eggs of reptiles (complete life cycle on land, opening terrestrial habitats)
-evolution of flowers (attract insect pollinators) (key innovation in history of flowering plants)
adaptive zone may open after demise of successful group
-ex. replacement of memmals multituberculata by rodentia
-beginning of Cambrian, 600 million years ago, disappearance of soft-bodied organisms and appearance of extraordinary
-change from soft to hard body reflected in fossil records (reasons for switch still not clear)
3.3b Islands: Showcases of Evolution
adaptive radiations: occur when an evolutionary breakthrough allows diversification of life
-recurring theme in development of biodiversity
-result is a mosaic of life, with many examples of parallel and convergent evolution
ex. evolution of fauna and flora of the Hawaiian Islands (arguably most isolated landmasses in the world)
1778-captain Cooke- 2000 species of higher plants, arisen from 275 ancestral stocks. Also about 6500 species of insects
from 250 ancestral stocks. 600 to 700 species in the genus Drosophila.
many plants undergone adaptive radiations. Violets shrubs, lobelias tree like
-occurred in absence of plants filling shrub and tree life styles
one ancestral insect and plant species gained access to Hawaii in each of the 25 000 to 100 000 years the islands were above water.
Galapagos Islands – Darwin – showcases of evolution and adaptive radiation
island populations of animals and plants can be very vulnerable to extinction
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