1. Objectives: 1)Describe how natural variation is used in artificial selection. 2)Explain how natural selection is related to species’ fitness. 3)Identify evidence Darwin used to present his case for evolution. 4)State Darwin’s theory of evolution by natural selection.

2.  Publication of On the Origin of Species  Darwin’s ideas challenged fundamental scientific beliefs  Discussed his work with friends  Shelved his manuscript for years  Told his wife to publish it when he died

3.  Publication of On the Origin of Species (cont’d)  1858  Alfred Russel Wallace wrote an essay summarizing his thoughts on evolutionary change and sent it to Darwin  This caused Darwin to want to publish his findings

4.  Publication of On the Origin of Species (cont’d)  1859  Darwin published On the Origin of Species  Suggested a mechanism for evolution (natural selection)  Caused a sensation

5.  Blue Ticket Question  What event motivated Darwin to publish his ideas?

6.   Darwin received Wallace’s essay  Play: http://www.sciencechannel.com/games-and- interactives/charles-darwin-game/http://www.sciencechannel.com/games-and- interactives/charles-darwin-game/ Blue Ticket Answer

7.  Inherited Variation and Artificial Selection  1 of Darwin’s most important insights was that members of each species vary from 1 another in important ways

8.  Inherited Variation and Artificial Selection (cont’d)  Variation exists both in nature and on farms  Heritable variation— differences that are passed from parents to offspring  Happened in the wild  Revolutionary idea

9.  Inherited Variation and Artificial Selection (cont’d)  Animal breeders use heritable variation (genetic variation) to improve crops and livestock  Selected only the organism that had the desirable traits to reproduce (artificial selection)

10.  Inherited Variation and Artificial Selection (cont’d)  In artificial selection, nature provided the variation, and humans selected those variations that they found useful  Has produced many diverse domestic animals and crop plants

11.  Evolution by Natural Selection  Darwin compared processes in nature to artificial selection  Developed a scientific hypothesis to explain how evolution occurs  Greatest contribution

12.  The Struggle for Existence  Struggle for existence: members of each species compete regularly to obtain food, living space, and other necessities of life  Predators—catch more prey if they are faster, etc.  Prey—survive if they are better protected

13.  Survival of the Fittest  A key factor in the struggle for existence is fitness  Fitness: the ability of an individual to survive and reproduce in its specific environment

14.  Survival of the Fittest (cont’d)  Darwin suggested that fitness is the result of adaptations  Adaptations: any inherited characteristic that increases an organism’s chance of survival  Successful adaptations allow organisms to become better suited to their environment to survive and reproduce

15.  Survival of the Fittest (cont’d)  Adaptations can be  Anatomical (structure)  Characteristics  Physiological processes (functions)  Behavior  Live  Hunt

16.  Survival of the Fittest (cont’d)  The concept of fitness was central to the process of evolution by natural selection  Survival of the fittest  Organisms that are not well suited to their environment  Die  Leave few offspring  Organisms that are better suited to their environment  Survive  Reproduce more successfully

17.  Survival of the Fittest (cont’d)  In natural selection  Only certain individuals of a population produce new individuals  The traits being selected contribute to an organism’s fitness in its environment  Takes place without human control or direction

18.  Survival of the Fittest (cont’d)  Over time, natural selection results in changes in the inherited characteristics of a population  These changes increase a species’ fitness in its environment

19.  Survival of the Fittest (cont’d)  Cannot be seen directly  Observed as changes in a population over many successive generations

20.  Blue Ticket Question  What did Darwin mean when he described certain organisms as “more fit” than others?

21.   Organisms that are better suited to survive in their environment and pass their traits on to the next generation Blue Ticket Answer

22.  Descent with Modification  Darwin suggested that over long periods of time, natural selection produces organisms that have different structures or occupy different habitats  Species today look different from their ancestors

23.  Descent with Modification (cont’d)  Descent with modification: each living species has descended, with changes, from other species over time  Implies that all living organisms are related to one another

24.  Descent with Modification (cont’d)  Common descent: all species—living and extinct—were derived from common ancestors

25.  Evidence of Evolution  Darwin argued that living things have been evolving on Earth for millions of years.  Evidence for this process  Fossil record  Geographical distribution of living species  Homologous structures of living organisms  Embryology (similarities in early development)

26.  The Fossil Record  Darwin suggested that Earth was many millions of years old  Countless species had come into being, lived for a time, and then vanished

27.  The Fossil Record (cont’d)  Scientists document the fact that life on Earth has changed over time by comparing fossils from older rock layers with fossils from younger layers  Fossils point out uncertainties in our understanding of exactly how some species evolved

28.  Geographic Distribution of Living Species  Darwin’s theory of descent with modification made scientific sense of why he sometimes saw different animals that had similar anatomies and behaviors

29.  Geographic Distribution of Living Species (cont’d) 1)Species now living on different continents had each descended from different ancestors 2)Some animals on each continent were living under similar ecological conditions and were exposed to similar pressures of natural selection 3)Different animals ended up evolving certain striking features in common

30.  Homologous Body Structure  Homologous structures: structures that have different mature forms but develop from the same embryonic tissues  Provides strong evidence that all 4-limbed vertebrates have descended, with modifications, from common ancestors

31.  Homologous Body Structure (cont’d)  Similarities and differences help biologists group animals according to how recently they last shared a common ancestor

32.  Homologous Body Structure (cont’d)  Vestigial organs: organs so reduced in size that they are traces of homologous organs in other species  The presence of a vestigial organ may not affect an organism’s ability to survive and reproduce  Natural selection would not cause the elimination of that organ

33.  Similarities in Embryology  The early stages (embryos) of many animals with backbones are very similar  The same groups of embryonic cells develop in the same order and similar patterns to make the tissues and organs of all vertebrates  Make homologous structures

34.  Blue Ticket Question  What are homologous structures?

35.   Homologous structures are structures that have different mature forms but develop from the same embryonic tissue Blue Ticket Answer

36.   Organisms  Differ, and some variation is heritable  Make more offspring than can survive and many that do survive do not reproduce  Compete for limited resources  Have different advantages and disadvantages in the struggle for existence  Pass their heritable traits to their offspring (natural selection)  Are descended with modification from ancestral species that lived in the distant past  Evolved from common ancestors (tree of life) Summary of Darwin’s Theory

37.  Strengths and Weaknesses of Evolutionary Theory  Scientific advances have confirmed and expanded most of Darwin’s hypotheses  Evolutionary theory continues to change as new data are gathered and new ways of thinking arise

38.  15-3 Exit Ticket