The Theories of Evolution

1. The Theories of Evolution Species change over time!!!

2. Species evolve (change) over time. • Evolution is the consequence of the interactions of • (1) the potential for a species to increase its numbers • (2) the genetic variability of offspring due to mutation and recombination of genes • (3) a finite supply of the resources required for life • (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring

3. Evolutionary Foundation • Hutton and Lyell helped scientists recognize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present. • Lamarckproposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species = Adaptation • Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.

4. Introducing Evolutionary Theory • We share Earth with millions of other organisms (variety of living things) = Biological Diversity • How is everything so different? • Evolution = change over time leading to modern organisms that have descended from ancient organisms • Theory = well-supported testable explanation of phenomena that have occurred in the natural world

6. Introducing… Charles Darwin! • In 1831, Darwin set sail on the Beagle for a voyage around the world • During his travel, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time = The Theory of Evolution • Darwin used these observations to scientifically explain the diversity of life on this planet.

7. The Galapagos Islands • Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands. Pinta IslandIntermediate shell Hood Island Saddle-backed shell Isabela Island Dome-shaped shell

8. Natural Variation & Artificial Selection • Natural Variation = differences among individuals of a species • Variations can be inherited from one generation to the next • Selective breeding = humans select desirable traits and breed based on natural variation (to improve crops/farms) • Darwin called this artificial selection = nature provides variation among different organisms, and humans select variations they found useful.

9. Evolution by Natural Selection • Living things evolve as the result of: • The struggle for existence • The survival of the fittest • The descent with modification Peacock tail evolution: http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html

10. Struggle for Existence • Darwin was convinced artificial selection worked in nature as the result of overproduction and competition for resources = struggle for existence (members of each species compete regularly to obtain food, living space, and other necessities of life) • Depends on an individual’s ability to survive and reproduce = fitness • Fitness results from adaptations = inherited characteristics that increase an organism’s chance of survival • = “Survival of the Fittest!”

11. Natural Selection • Survival of the fittest = Natural Selection! • Traits are being selected and increasing over time (over many generations without human influences) • Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment.

12. Descent with Modification • Over time, natural selection produces organisms with different structures or functions resulting in species that look different from their ancestors • Each living species has descended with changes from other species over time = Descent with Modification • Then, all living things must be related! • There’s a common ancestor of all living things = Common Descent

13. Living things have been evolving on Earth for millions of years. Evidence of this process could be found in: The fossil record The geographical distribution of living species Homologous structures of living organisms Similarities in development Evidence of Evolution

14. Fossil Record • Remember: Fossils are the remains of ancientlife and different layers of rock were formed at different times. • Fossils in different layers of rock are evidence of the gradual change over time (different species appeared, lived for a time, and then vanished)

16. Geographic Distribution • Populations in different places adapted to different environments… different species descended with modification from a common ancestor. • Different species living in similar environments in different parts of the world sometimes have similar structures and functions because they experienced similar pressures of natural selection

17. Homologous Structures • Some vertebrates have similar bone structures that develop from a specific group of cells in an embryo, but the structures adapted different functions so the organism can survive in different environments providing evidence of descent with modification from common ancestors • Homologous Structures = they appear and function differently, but develop from the same embryonic tissues • Some homologous structures provide little or no function in some organisms = vestigial organs

18. Similarities in Development • Embryos of many vertebrates look very similar in the early stages of development. • The same groups of embryonic cells develop in the same order and in similar patterns producing homologous structures

19. Individual organisms in nature differ, and some variation is inherited Organisms in nature produce more offspring than can survive and reproduce Members of each species compete for limited resources Unique organisms have different advantages and disadvantages in the struggle for existence Individuals best suited to their environment survive and reproduce, passing the characteristic to their offspring. Individuals without the characteristic die Species change over time due to natural selection… new species arise and others disappear Species alive today have descended with modification from species of the past All organisms on Earth are united by a common descent Summary of Darwin’s Theory