15.3 Darwin Presents his Case. Biology Mr. Hines

Transcription

1 15.3 Darwin Presents his Case Biology Mr. Hines

2 Darwin returned to England with a wealth of new data. He brought many specimens from the Galapagos to further his studies and to present his data to others.

3 After further study, he discovered that the tortoises, finches, and marine iguanas were found no where else in the world. However, many of these species were similar to those found on the West coast of South America

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5 Publication of the Origin of Species Because Darwin s ideas clashed with the ideals of his time, he was hesitant to publish his findings he waited 25 years 25 years later, Darwin read a short essay by a scientist named Wallace, who used some of Darwin s findings as evidence for evolutionary change. Darwin was inspired by this essay and decided to publish his own work.

6 In 1859, Darwin published On the Origin of Species. In this book, he proposed the mechanism for natural selection. He presented his evidence that natural selection has been going on for millions of years. Many thought of his work as brilliant while others strongly opposed his message (noncritical thinkers)

7 Inherited Variation and Artificial Selection One important observation is that individuals within a species are slightly different from one another this is called genetic variation. For example humans all have 2 arms, 2 legs, 1 head, 2 eyes, and a small brow above the eyes. Still, no two humans look the same this is genetic variation within a species. This is true of all species (have you ever seen 2 trees grow the same way?)

8 Variation can exist in 2 places 1. Farms 2. Nature On farms, farmers can select which animals will breed. Some cows will produce more milk than others. So when the cows are selected for mating, those that produce more milk will be mated while low producing cows will not.

9 Eventually, all cows will be producing lots of milk. Therefore the trait for high milk production is inherited by the offspring. This is called artificial Selection the farmer selected who would mate Artificial Selection Nature provides the genetic variation, humans select the traits they find useful. Farmers do this with all products including crops to yield greater amounts.

10 Today we know that variation among species is due to variations located in the genes (chromosomes) Again, this is called genetic variation. Darwin argued that this variation found in nature mattered a great deal. Artificial selection has produced many diverse domestic animals and crop plants.

11 Did you know that all of these vegetables were bred from one common ancestor

12 Evolution by Natural Selection If farmers could control evolution, how about the natural world? Darwin was convinced that selection also worked in nature.

13 The struggle for existence Darwin realized that most animals produced several offspring most of which would not survive. These offspring would have to Struggle for existence. Since there is not enough food and living space for them all, the stronger offspring would out-compete the weak. Therefore the stronger will live and the weak will die.

14 Example Lions must be fast enough to catch their prey a deer. If the lion is not fast enough, it will die. There will not be enough deer for all Lions, therefore, fast lions live, slow lions die. Nature has selected the faster lion to live and the slower lion to die Natural selection.

15 Survival of the Fittest A factor in the struggle for existence is how well suited an animal is to its environment. The ability of an individual to survive and reproduce in its specific environment is called FITNESS. In other words, an animal that survives and reproduces successfully in its environment it FIT. Or fit to survive.

16 Fitness is a result of adaptations. Adaptation any inherited characteristic that increases an organism s chance of survival. Successful adaptations enable organisms to become better suited to their environment and thus better able to survive and reproduce.

17 Here are some examples of camouflage animals that have adapted to their environment Example with photo.

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23 There are several types of adaptations here are 3 1. Structural porcupines sharp quills 2. Physiological chemical manner in which a plant processes photosynthesis 3. Behavioral lions hunt in groups instead of individuals.

24 Fitness is central to the process of evolution by natural selection. Generation after generation for millions of years individuals compete for existence. Change is inevitable. Survival of the fittest Those organisms that are best suited for their environment will survive and reproduce passing on the needed adaptation to the offspring.

25 This process is called Natural Selection. This is similar to the farmer and his crops only nature selects who lives and who dies based on fitness. Natural selection insures that each generation is fit to the environment. Fitness increases over time. Natural selection cannot be seen directly; it can only be observed over many generations.

26 Descent with modification Darwin proposed that, over long periods of time, natural selection will produce animals with different structures which will establish new habitats. As a result, species will look different today as they did in the past (their ancestors) This principle is known as descent with modification.

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29 Descent with modification implies that all living things are related to one another - The fossil record shows how fish adapt legs and lungs (rib cage) and eventually crawl on to land.

30 these animals are no longer living, but their offspring are they are called amphibians.

31 Life cycle of frog This is evidence that amphibians evolved from fish. This is an example of descent with modification

32 As you follow the trail of descent backwards, you end up finding that all living things are related. Common descent the concept that all living things are related.

33 Evidence for Evolution There are 4 main bodies of evidence for evolution 1.The fossil record 2. Geographic distribution of living species 3. Homologous body structures 4. Similarities in embryology (the study of embryos) We will take a close look at these 1 by 1.

34 The fossil record Fossils are the remains of ancient life. They can be found all over the earth buried within the layers of rock and soil which was deposited as the earth changed. This is evidence that the earth is millions of years old, not thousands as once believed.

35 During this time span, the fossil record indicates that countless species had come into being, lived for a time, and then vanished. By comparing the different fossils from older rock layers with fossils of younger layers, scientists can document the fact that life has changed over time.

36 Since Darwin s time, the number of known fossils has grown enormously. We can trace the ancestry of most animals backwards in time. There are many transitional fossils which connect extinct animals to animals living today. I should point out that there are gaps in the fossil record. As humans find more fossils, these gaps are expected to close.

37 The fossil record shows descent of the nautilus shown to the right.

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39 Transitional fossils of Homos This is called Anthropology

40 Geographic Distribution of Living species Most of Darwin s observations were of living things. Again, we will talk about the finches on the Galapagos islands. Darwin noticed that the Galapagos finches were similar to the finches on the mainland of South America, yet there were also differences. He wondered if the birds flew over from the mainland and changed over time. In other words, they all have a common ancestor from the mainland.

41 Descent with modification makes perfect sense here. Because of the similarities of various habitats found on different continents, animals that look very similar have descended from different ancestors.

42 The Beaver and the Capybara

43 This demonstrates that animals can evolve separately on different continents, and end up with similar traits for survival. The environment can put pressure on evolution.

44 Homologous body structures Much evidence of evolution comes within living things particularly the animals with backbones. There are many anatomical similarities among body parts. For example, Reptiles, birds, and mammals arms, wings, legs, and flippers all vary greatly in form and function, yet they are all made from the same bones.

45 These are known as homologous body structures

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47 These homologous body structures are evidence that all vertebrates have a common ancestor of fish. In an embryo, all homologous body structures develop the same, they just have different mature forms.

48 Not all homologous structures are useful. Some limbs are reduced in size because they are not important for survival. Skinks have tiny legs that they don t really use. The mostly move around like snakes.

49 Skinks vestigial organs

50 Snakes have vestigial legs under their skin evidence that they once had legs.

51 Whales have vestigial legs

52 The study of homologous structures is called homology How do you tell if a dolphin is more closely related to fish or mammals? Look at the homologous structures dolphins are mammals.

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54 Similarities in embryology Because the development of embryos of all vertebrates is similar, it can be argued that all vertebrates have a common ancestor.

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56 Summary Individual organisms differ, and some of this variation is heritable. Organisms produce more offspring than can survive, and many that do survive do not reproduce. Because more organisms are produced than can survive, they compete for limited resources. Each unique organism has different advantages and disadvantages in the struggle for existence. Individuals best suited to their environment survive and reproduce most successfully. These organisms pass their heritable traits to their offspring. Other individuals die or leave fewer offspring. This process of natural selection causes species to change over time. Species alive today are descended with modification from ancestral species that lived in the distant past. This process, by which diverse species evolved from common ancestors, unites all organisms on Earth into a single tree of life