lecture 2

Natural selection is one mechanism of change natural

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Unformatted text preview: odification, or evolution, describes the changes of organisms through time. •  Natural Selection is one mechanism of change •  Natural Selection is the process that leads to adaptation 2 9/30/12 Deductive reasoning for evolution by natural selection •  Observation #1: For any species, population sizes would increase exponentially –  If all individuals that are born reproduced successfully –  This is the argument of ? •  •  •  •  •  A Lyell B Cuvier C Copernicus D Malthus E Darwin Figure 22.8 •  Observation #2: Nonetheless, populations tend to be stable in size •  Observation #3: Resources are limited –  Inference #1: Production of more individuals than the environment can support •  Leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving •  This is the inference Darwin arrived at after reading Malthus. •  Observation #4: Members of a population vary extensively in their characteristics –  No two individuals are exactly alike Figure 22.9 3 9/30/12 •  Observation #5: Much of this variation is heritable –  Experiments in plant and animal breeding prove this. •  Inference #2: Survival may depend in part on inherited traits Terminal Lateral buds bud Brussels sprouts Cabbage Flower cluster Leaves Cauliflower Kale Flower and stems Broccoli –  Individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals Stem Wild mustard Kohlrabi Figure 22.10 •  Inference #3: The unequal ability of individuals to survive and reproduce –  Will lead to a gradual change in a population, with favorable characteristics accumulating over generations •  This is the process called Natural Selection –  All that is required for this process is heritable (that is, genetic) variation that affects fitness Summary of Natural Selection •  Natural selection is diff...
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