Change Through Time

1. Change Through Time Unit 5 Chapter 15

2. Theory of evolution • Charles Darwin’s theory is the core of modern biology. • His idea explains how organisms have changed over time, not how the first organisms on Earth came to be. • Evolution is a theory and not a hypothesis.

3. Misconceptions of evolution • Many people think that Darwin’s theory states that man evolves from monkeys or apes. • This is untrue. Evolutionary theory suggests that humans and all primates share some common ancestors in the past. • Many people think that evolution disproves religion. • This is untrue. Evolution cannot prove or disprove religion. Evolution only states how species can change genetically over time.

4. Misconceptions of evolution • Many people think that Darwin invented evolution. • This is untrue. Alfred Russell Wallace proposed the concept of “survival of the fittest.” Jean Baptiste Lamarck proposed the “use or disuse” hypothesis. Because Lamarck’s work was scientifically unsound, many confuse Lamarckian evolution with Darwinian evolution. Lamarck believed that if, for example, the trees are tall, horse-like animals could grow simply long necks to eat the leaves, therefore evolving a giraffe.

5. Misconceptions of evolution • Many people believe that evolution always changes a species to make the species better. • This is untrue. Evolution is a process that shows species can change over time. Whatever genes are best adapted for survival in a given time period will survive and be passed onto future generations. These environment in the future may be very different, and the genes passed down may no longer be best adapted to the environment.

6. Evidence for evolution • DNA analysis • Fossil records • Morphological comparisons • Embryology

7. Darwin on the HMS Beagle • He began in 1831 at age 22 when he took a job as a naturalist on the English ship HMS Beagle, which sailed around the world on a five-year scientific journey.

8. Darwin on the HMS Beagle • As the ship’s naturalist, Darwin studied and collected biological and fossil specimens at every port along the route. • On the Galápagos Islands, Darwin studied many species of animals and plants that are unique to the islands but similar to species elsewhere. • These observations led Darwin to consider the possibility that species can change over time.

9. The work of Thomas Malthus • English economist Thomas Malthus had proposed an idea that Darwin modified and used in his explanation. • Malthus’s idea was that the human population grows faster than Earth’s food supply.

10. Malthus influencing Darwin • Darwin knew that many species produce large numbers of offspring. • He also knew that such species had not overrun Earth. • He realized that individuals struggle to compete in changing environmental conditions. • Only some individuals survive the competition and produce offspring, a concept called fitness.

11. Formulating the theory of natural selection • Darwin observed that the traits of individuals vary in populations and are inherited. • Artificial selection or breeding of specific animal and plant traits has long been practiced. • Darwin hypothesized that there was a force in nature that worked like artificial selection

12. Natural selection • Natural selection is a mechanism for change in populations. • It occurs when organisms with favorable variations survive, reproduce, and pass their variations to the next generation. • Organisms without these variations are less likely to survive and reproduce. • As a result, each generation consists largely of offspring from parents with these variations that aid survival. • Natural selection is what causes evolution.

13. Natural selection example • Fishes may differ in color, size, and speed. • Individuals with certain useful variations, such as speed, survive in their environment, passing those variations to the next generation.

14. Natural selection example • Over time, offspring with certain variations make up most of the population and may look entirely different from their ancestors.

15. Adaptation: any variation that aids an organism’s chances of survival in its environment • According to Darwin’s theory, adaptations in species develop over many generations. • Adaptations to the body’s structure within one or two generations is Lamarck’s ideas. • Remember that Lamarck believed if an animal needs more fur to stay warm and can grow more fur, this is the concept of “use and disuse” not evolution or adaptation.

16. Adaptation example • The ancestors of today’s common mole-rats probably resembled African rock rats.

17. Adaptation example • Some ancestral rats may have avoided predators better than others because of variations such as the size of teeth and claws.

18. Adaptation example • Ancestral rats that survived passed their variations to offspring. • After many generations, most of the population’s individuals would have these adaptations.

19. Adaptation example • Over time, natural selection produced modern mole-rats. • Their blindness may have evolved because vision had no survival advantage for them.

20. Mimicry • a structural adaptation that enables one species to resemble another species • Many harmless insects and snakes resemble harmful species, which fools predators

21. Mimicry • Yellow jacket hornets, honeybees, and many other species of wasps all have harmful stings and similar coloration and behavior. • Predators may learn quickly to avoid any organism with their general appearance.

22. Camouflage • an adaptation that enables species to blend with their surroundings • Because well-camouflaged organisms are not easily found by predators, they survive to reproduce

23. Evolution of drug resistant bacteria Today, penicillin no longer affects as many species of bacteria because some species have evolved physiological adaptations to prevent being killed by penicillin. Non-resistant bacterium Antibiotic Resistant bacterium When the population is exposed to an antibiotic, only the resistant bacteria survive. The resistant bacteria live and produce more resistant bacteria. If bacteria can develop drug resistance in just a few generations, imagine the changes to some bacteria over millions of years.

24. Fossil evidence of evolution • They provide a record of early life and evolutionary history.

25. Incomplete fossil record • Although paleontologists do not have fossils for all the changes that have occurred, they can still understand the overall picture of how most groups evolved. • As the fossil record becomes more complete, the sequences of evolution become clearer.

26. Example of using fossil record Camel Evolution Oligocene 33 million years ago Miocene 23 million years ago Eocene 54 million years ago Paleocene 65 million years ago Age Present Organism Skull and teeth Limb bones

27. Structural features with a common evolutionary origin are called homologous structures. Homologous structures can be similar in arrangement, in function, or in both. Comparing anatomy Crocodile forelimb Bird wing Whale forelimb

28. Comparing anatomy • The body parts of organisms that do not have a common evolutionary origin but are similar in function are called analogous structures. • Example: Insect and bird wings probably evolved separately when their different ancestors adapted independently to similar ways of life.

29. Vestigial organs • a body structure in a present-day organism that no longer serves its original purpose, but was probably useful to an ancestor • Vestigial structures, such as pelvic bones in the baleen whale, are evidence of evolution because they show structural change over time.

30. Embryology • An embryo is the earliest stage of growth and development of both plants and animals. • The embryos of a fish, a reptile, a bird, and a mammal have a tail and pharyngeal pouches. Pharyngeal pouches Pharyngeal pouches Mammal Reptile Bird Fish

31. Embryology • Shared features in the young embryos suggest evolution from a distant, common ancestor Pig fetus – 21 days Human fetus – 31 days

32. Biochemical evidence for evolution • Nearly all organisms share DNA, ATP, and many enzymes among their biochemical molecules. • Example: Cytochrome c enzyme occurs in organisms as diverse as bacteria and bison. Biologists compared the differences that exist among species in the amino acid sequence of cytochrome c.

33. Comparing amino acid sequences • The number of amino acid substitutions in the amino acid sequences for the different organisms. • Related organisms have fewer differences in their amino acid sequences. Biochemical Similarities of Organisms 5 and 10 Percent Substitutions of Amino Acids in Cytochrome c Residues 8-12 Comparison of Organisms 14-18 Two orders of mammals 18-22 Birds vs. mammals 27-34 Amphibians vs. birds 57 Fish vs. land vertebrates Insects vs. vertebrates Algae vs. animals

34. Using biochemical evidence • In the 1970s, some biologists began to use RNA and DNA nucleotide sequences to construct evolutionary diagrams. • Today, scientists combine data from fossils, comparative anatomy, embryology, and biochemistry in order to interpret the evolutionary relationships among species.

35. Population genetics • If an organism has a feature (phenotype) that is poorly adapted to its environment, the organism may be unable to survive and reproduce. • However, within its lifetime, it cannot evolve a new phenotype by natural selection in response to its environment. • Natural selection acts on the range of phenotypes in a population.

36. Population evolves, not the individual. • All of the alleles of the population’s genes as are together in a large pool called a gene pool. • The percentage of any specific allele in the gene pool is called the allelic frequency. • They refer to a population in which the frequency of alleles remains the same over generations as being in genetic equilibrium. • A population that is in genetic equilibrium is not evolving.

37. Evolution and equilibrium • Any factor that affects the genes in the gene pool can change allelic frequencies. • This disrupts a population’s genetic equilibrium. • This results in the process of evolution.

38. What can disrupt genetic equilibrium? • Mutation • Natural selection • Genetic drift: random natural events that change gene frequency • Gene flow • Introducing new genes from individuals migrating into the population • Reducing the genes from individuals leaving the population

39. Speciation • The evolution of new species, a process called speciation occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment. Gradualism: Speciation can occur slowly as Darwin proposed. • Punctuated equilibrium: Speciation can occur rapidly followed by periods of no evolution. • Realistically, speciation occurs by both methods.

40. Gradualism Loxodonta africana Elephas maximus 0 1 2 Millions of Years Ago Mammuthus primigenius Elephas 3 Loxodonta 4 Mammuthus 5 Primelephas 6 Ancestral species about 55 million years ago

41. Adaptive radiation • When an ancestral species evolves into an array of species to fit a number of diverse habitats, the result is called adaptive radiation.