1. Science 20 – Biology Ch. 2 Populations Lesson 18

2. Changes in Population Very gradual changes within a population are called gradualism –e.g. changes to the shape of a shell for a snail population over time Punctuated equilibrium – theory that states changes to organisms in a population can occur in rapid spurts followed by long periods of little change

3. Case study: Punctuated Eq. e.g. Alberta’s Bighorn Sheep population Hunters are only allowed to shoot rams if their horns have curved to almost make a circle (trophy sheep) The largest & strongest male sheep are the ones with fully curved horns

4. Since they are being removed by hunters, the male sheep left to breed are smaller & weaker (they never mature to trophy status) The male sheep in the next generations tend to have decreased body mass & shorter horns Hunting is inadvertently encouraging these characteristics in a short time

5. A change in instructions from a gene is a mutation  this is another reason why variation occurs in a species (it can be harmful, beneficial, or neutral) Mutations can sometimes be beneficial  the development of a new characteristic or trait might increase an organism’s chances for survival

7. Variation a difference in the frequency of genes & traits among individual organisms within a population e.g. the ability to roll your tongue, hitchhikers thumb, or widows peak.

8. Adaptation Any structural OR behavioral trait that improves an organism’s success at surviving & reproducing in a particular environment

9. Galapagos Finches  Charles Darwin observed a chain of volcanic islands off the Pacific coast of South America called the Galapagos Islands  There were a variety of different climatic regions, each with their own unique ecosystem along the islands with a variety of food sources  Darwin observed that the same animals had adapted differently to take advantage of the local conditions

10. E.g. Several varieties of finches had different beak types that were adapted for a diet specific to their regions Darwin suggested that all varieties of finches came from a common seed-eating finch ancestor

11. Darwin’s Theory of Evolution Published “On the Origin of Species by Means of Natural Selection” to describe his theory of evolution – theory stating that the nature of population gradually changes form over time

12. Darwin also described his theory of natural selection based on the following observations: Organisms usually produce more offspring than can survive There is a variation among individuals with respect to any trait in a population Organisms within a population compete for limited resources

13. The best adapted individuals in the population are considered to have greater Darwinian fitness because they’ll be able to survive, breed, & pass on traits Reproductive success of an organism

14. More Evidence The fossil record indicates that organisms did not remain static

15. Many organisms have vestigial structures – structures that serve no function. (i.e. appendix in humans, undeveloped hind legs in a whale.)

16. Homework Read p.494-495 first Practice Question #29-32

17. Homework Case Study in readings: James Lamark (Incorrect Hypothesis) and The Peppered Moth Assignment: p.500-503 #36-40a, 42-46