Darwinian Evolution Chapter

Slide 2 of 20 Galapagos Islands  Darwin visited the Galapagos Islands  He formed his ideas about natural selection here  Why were the Galapagos Islands a good place to study natural patterns?  Variation – difference in physical traits of an individual from those of the other members in the group  Darwin took note of the variation of organisms via each island in the Galapagos

Slide 3 of 20 Different environments  Long necked and legged tortoises lived in areas with mostly tall plants.  Tortoises with a short neck and legs, lived in areas with short plants and mosses.  Animals could adapt to their environment?

Slide 4 of 20 Adaptation  Adaptation – feature that allows an organism to better survive in its environment  Adaptations can lead to a genetic change in a population over time  Evolution – genetic change in a population over time  So adaptations can lead to ______ ?

Slide 5 of 20 Ancient Earth?  Darwin found fossil evidence of ancient & extinct organisms that were similar but different than currently living (extant) forms.

10.3 – How does Evolution occur?

Slide 7 of 20 Selection  Darwin observed that domesticated plants and animals displayed variation that was not found in their wild counterparts  Through selection of animals with particular traits, breeders could produce a great amount of diversity  Artificial selection – humans select for certain traits, and preferentially breed those animals in possession of those traits  Called artificial selection since humans are selecting for certain traits that they deem desirable

Slide 8 of 20 Heritability  In order for a trait to be selected for, artificial or natural, trait must be inherited  Heritability – the ability of a trait to be passed down from one generation to the next 

Slide 9 of 20 Natural Selection  Natural Selection – mechanism by which individuals that have inherited favorable adaptations produce MORE offspring on average than do other individuals  Environment is the selective agent  Characters are selected only if they confer some advantage to those who have it

Slide 10 of 20 Conditions for Natural Selection  Struggle for survival  Resources are limited  Space, food, mating opportunities  Wants are Unlimited  Organisms can produce more offspring than the environment can provide for  Certain adaptations seemed well-suited for their environment

Slide 11 of 20 4 Principles for Theory of Natural Selection  1. Variation  the heritable differences are the basis for natural selection  2. Overpopulation  If the population is supported by the environment, no selection will occur  3. Adaptation  Certain individuals have favorable variation that enables them to be better suited to their environment  4. Descent with Modification  Natural selection will result in populations that are better suited to survival and reproduction in an environment

Slide 12 of 20 VARIATION OVERPRODUCTION ADAPTATION

Slide 13 of 20 Imperfect Organisms  Why are organisms not perfectly adapted to their environment?  Natural selection works on EXISTING variation  Natural selection can only modify what is there, so perfect structures are not always possible  Could a human ever be able to lift 18 tons (36,000 pounds)?  Could a human ever be able to develop gills for underwater existence?

Slide 14 of 20 Evidence for Evolution  Fossils  Okay  Biogeography  Good  Embryology  Excellent  Anatomy  Excellent  Genomics

Slide 15 of 20 Fossils provide evidence of evolution. Fossils in older layers are more primitive than those in the upper layers.

Slide 16 of 20 The study of geography provides evidence of evolution. –island species most closely resemble nearest mainland species –populations can show variation from one island to another

Slide 17 of 20 Embryology provides evidence of evolution. Larva Adult barnacle Adult crab –identical larvae, different adult body forms –similar embryos, diverse organisms

Slide 18 of 20

Slide 19 of 20 The study of anatomy provides evidence of evolution. Human hand Bat wingMole foot –Homologous structures are similar in structure but different in function. –Homologous structures are evidence of a common ancestor.

Slide 20 of 20 Human hand Bat wing Mole foot Fly wing Analogous structures are not evidence of a common ancestor. Analogous structures have a similar function.

Slide 21 of 20 Vestigial structures are remnants of organs or structures that had a function in an early ancestor. Ostrich wings are examples of vestigial structures. Vestigial Structures

Slide 22 of 20 Paleontology provides evidence to support evolution.

Slide 23 of 20 Molecular and genetic evidence support fossil and anatomical evidence.  Two closely-related organisms will have similar DNA sequences.