Chapter 15 Evolution 15 1 Darwins Theory of

Chapter 15: Evolution 15. 1 Darwin’s Theory of Evolution by Natural Selection 1

Charles Darwin • Charles Darwin was a naturalist, and explored the Galapagos islands, collecting rocks, fossils, plants, and animals – Entire voyage of The HMS Beagle: Dec 1831 - Oct 1836 • When and where he started thinking about what was to become his theory of evolution by natural selection. • He did not publish his thoughts until the 2 publication of The Origin of Species in 1859.

Charles Darwin’s Ideas • Biological evolution is change in species over time. – This was not a new idea at the time – But there were no good mechanisms to explain how these changes occurred • Natural selection is just such a mechanism, and this is what Darwin contributed. 3

The Galapagos Islands • Located approximately 1000 km from the coast of Ecuador, South America. • This is just a little closer than the distance between Chicago and Philadelphia. – Mostly ground between the two U. S. cities. – Mostly deep water between the Galapagos Islands and the coast of South America. 4

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Implications • Terrestrial species on these islands won’t have many relatives nearby. • Neighboring islands will have close relatives – but new terrestrial species won’t arrive on these islands from the South American mainland very often. – most of the island species have had plenty of time to differentiate from their nearest living relatives. • Another way of saying this is that there is very little gene flow between the islands and the mainland. 7

Q 1: Limited gene flow means: A: Birds rarely move between the mainland the islands. B: Birds on the island have the same genes as birds on the mainland. C: Birds on the mainland don’t like birds from the islands. D: Birds on the mainland won’t evolve, but birds on the islands might. 8

Peter and Rosemary Grant • Scientists Peter and Rosemary Grant have studied many of the various Finch species for the past thirty years. – Spend months at a time on the islands – Often know every finch on an island • Let’s look at some of their data. 9

Graph showing the distribution of beak depths for medium ground finches in Year 1 10

Q 2: What is the average depth of the finches’ beaks in Year 1? A: about 7 mm B: about 8 mm C: about 9. 5 mm D: about 10 mm E: about 11 mm 11

A Change in the Weather • Year 2 • Like most years, some rain fell the first week of January. – The rest of January, there was one small shower. – The total rainfall for the entire year: 24 mm. • In a normal year, 130 mm of rain would fall. • In Year 1, 137 mm of rain fell. 12

Weather effects on Finch population • The ground finches feed on seeds. • In the drought, the plants conserved their resources and did not produce new seeds. • Similarly, the finches did not mate and did not produce eggs in Year 2 13

Prediction? • What do you think will happen to the size of the finch population between Years 1 and 3? (Remember, Year 2 is a drought year. ) • Talk with your group and sketch a graph on your whiteboard of what the finch population will look like 14

Q 3: What do you think a graph of population size would look like for Year 1 to Year 3? B: A: Time C: Time D: Time 15

Year 3 Data 16

Q 4: What was the average beak depth in 1978? (Remember that the average beak depth in 1976 was 9. 5 mm. ) A: Just under 7 mm B: About 8 mm C: About 9 mm D: Just under 10 mm E: Just under 11 mm 17

Evolution Defined Evolution is a change in the frequency of an allele, such as an allele for beak depth, is the basic definition of evolution. 18

Q 5: Did the finch population evolve from 1976 to 1978? A: Yes B: No C: Maybe D: I don’t know 19

Evolution by natural selection • The Grants first went to the Galapagos to take a quick snapshot of finch diversity. • Within only a few years, they saw natural selection. – In the course of one season, the beaks got 0. 54 mm deeper and 0. 39 mm longer. 20

Any Surprises? Evolution can occur at very small scales. The Grants’ measurements were very careful. • The birds weren’t used to humans, and so they were unusually easy to catch and measure • They couldn’t see a difference in even 1 mm between two finches, but their measurements could • And due to those measurements, they could find that 0. 5 mm was enough to make a difference between survival and death in a drought year 21

Heritability • It’s important to note that beak size and shape is heritable in these finches. – A bird with a large, deep beak will have offspring with large and deep beaks. • Natural selection can occur without heritability, but evolution by natural selection cannot! – (think about that for a minute…) 22

Q 6: If beak depth increased during the drought, primarily due to selective mortality, can we really say that this natural selection was driven by environment favoring the survival of birds with deeper beaks? A: No. Beak depth changed due to birds dying, not to birds surviving. B: Yes. Birds with deeper beaks survived at a higher rate than birds with shallower beaks. C: I’m really confused. 23

Evolution by Natural Selection (4 Principles) 1. Variation Individuals in a population differ from one another. I. e some sunflowers are taller than others Individuals vary in some traits. 2. Heritability Some of the differences in traits are passed along to offspring. This requires a genetic basis to the trait. The trait is thus heritable. i. e Tall sunflowers produce tall sunflowers, and short sunflowers produce short sunflowers. (more…) 24

Evolution by Natural Selection • 3. Overproduction-Populations produce more offspring than can survive. i. e. each sunflower has hundreds of seeds, most of which will not germinate. • 4. Reproductive Advantage- Some variations allow the organism that possess them to have more offspring then the organism that does not possess them. i. e. In different habitats shorter sunflowers reporduce more successfully. 25

Artificial Selection • Artificial Selection-the process of directed breeding to produce offspring with desired traits. (also proposed by Darwin. ) • This can be implemented by humans i. e new dog breeds or new strains of crop plants, and also naturally by nature (natural selection. ) 26

Artificial Selection • in the beef industry- beef producers “select genes” and phenotypic traits that produce them winning results and a better beef product. 27