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The General Principles of the Theory of Natural Selection

The General Principles of the Theory of Natural Selection. 1. There is natural variation in the populations of all organisms. Individual variation in the Grevy’s Zebra ( Equus grevyi) look closely at the patterns of each individual zebra, they are all different .

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The General Principles of the Theory of Natural Selection

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  1. The General Principles of the Theory of Natural Selection

  2. 1. There is natural variation in the populations of all organisms

  3. Individual variation in the Grevy’s Zebra (Equus grevyi)look closely at the patterns of each individual zebra, they are all different Check out this cute gluteal tattoo

  4. Plains Zebra (Equus quagga) How many differences in color pattern can you find between these two zebras?

  5. What about the facial patterns in this group? Notice that all are different. If you can see the difference, what do you think the zebras can determine? Yep, everyone is identifiable as a unique individual.

  6. Plains Zebra Grevy’s Zebra

  7. 2. Much of this variation is genetically inherited, roughly 50% from each parent, on average

  8. 3. More individuals are born to each generation than can survive- populations are kept at particular levels by natural “checks”- the Malthusian Principle

  9. 4. Certain forms of a character may be better suited for a particular environment or for a certain set of circumstances within that environment. A leopard that hunts using a “sit-and-wait” strategy (dropping down from a tree onto a passing impala) has little need for the speed of a cheetah, but does need powerful muscles and bone structure, especially to carry the prey back up the tree.

  10. Pepper Moth (Biston betularia) Classic example of a moth species with two color morphs, each adaptive under a different set of environmental circumstances. The principle predators of this moth are birds, which hunt using visual cues.

  11. Oopsie! Not such a good idea to be a white moth on a dark tree, such as this one which is covered with coal soot.

  12. Demoiselle Crane (Anthropoides virgo) A trait is said to be “adaptive” if it increases the likelihood that the offspring of the individual possessing it will survive. This is known as reproductive fitness. An individual is said to be “more fit” if it passes more individuals to the next generation. This crane has a single offspring (chick). Generally speaking, if it makes it to the next generation, the fitness value would be calculated as “1”.

  13. Another concept of “adaptiveness”: a trait which minimizes expended energy or risk and maximizes gain. This enhances individual survival, which, in turn, enhances reproductive fitness

  14. The Concept of “Sexual Selection”, a major contribution of Darwin to evolutionary theory A little tail never hurt anyone Widowbird (Euplectes progne)

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