The History of Life on Earth, The Theory of Evolution, and Populations

1. The History of Life on Earth, The Theory of Evolution, and Populations Chapters 12, 13 & 15 Notes

2. (Ch. 12) How Did Life Begin? • Most scientists think that life on Earth developed through natural chemical and physical processes. It is thought that the path to the development of living things began when molecules of nonliving matter reacted chemically during the first billion years of Earth’s history. These produced simple organic molecules which gained energy from the sun and volcanic heat to form more complex molecules that became the building blocks of cells. This hypothesis has been tested and supported in lab experiments. Many scientists have been, and are still, working on this. • The Miller – Urey model supports the theory but has since been brought into question because of the lack of ozone four billion years ago. • Scientists are still searching for the answers.

3. Miller-Urey Experiment Mixture of gases simulating atmospheres of early Earth Spark simulating lightning storms Cold water cools chamber, causing droplets to form Condensation chamber Water vapor Liquid containing amino acids and other organic compounds

4. The Evolution of Cells • The Evolution of Prokaryotes • The oldest known fossils are prokaryotes • The first prokaryotes were cyanobacteria – photosynthetic bacteria that live in water; they produced oxygen • There are 2 groups of prokaryotes: eubacteria and archaebacteria • they differ in their cell wall composition

5. The Evolution of Eukaryotes • The theory of endosymbiosis – a theory of how eukaryotic cells came to have mitochondria and/or chloroplasts • The theory says that bacteria entered larger cells as either parasites or undigested food. Once inside the cell, they began to live there • If the bacteria had been aerobic before entering the host cell, it turned into a mitochondrion that did aerobic respiration for the new host cell • If the bacteria had been photosynthetic before entering the host cell, it turned into a chloroplast that did photosynthesis inside the new host cell

6. EndosymbioticTheory Chloroplast Plants and plantlike protists Aerobic bacteria Ancient Prokaryotes Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Primitive Photosynthetic Eukaryote Animals, fungi, and non-plantlike protists Primitive Aerobic Eukaryote Ancient Anaerobic Prokaryote

7. More Endosymbiosis • These characteristics support the idea that mitochondria and chloroplasts started out as bacteria: • They are about the same size and shape as bacteria and have similar membranes • Mitochondria and chloroplasts have circular DNA similar to bacterial DNA • Their ribosomes are similar in size and structure to bacterial ribosomes • Bacteria, mitochondria and chloroplasts all reproduce the same way (binary fission) • ..\..\..\Pre-AP Biology\Content\Chapter 17B.mpg

8. Life Invaded the Land • With the formation of the ozone, multicellular organisms began to live on land • Plants and fungi were first • Arthropods were the first animals to invade land • Amphibians were the first vertebrates to invade land • Continental drift – the movement of Earth’s land masses, helped lead to reproductive isolation (because of geographic isolation)

9. (Ch. 13) The Theory of Evolution • Charles Darwin - He served as the ship’s naturalist and sailed around the world for five years on a ship called The Beagle, collecting specimens of plants, animals and fossils at each destination • The scientific thought at the time was that species did not change and they strongly believed in Creationism

10. Darwin’s Finches • On the Galapagos Islands, Darwin found species of finches that each had specialized beaks to catch food in different ways • He believed they descended from a common ancestor because of their shared similarities

11. Evolution by Natural Selection • Evolution – change in a species over time • Darwin’s book, On the Origin of Species by Means of Natural Selection (more commonly known as The Origin of the Species), presented his evidence that evolution occurred by means of natural selection – the process by which organisms with traits well suited to an environment are more likely to survive and produce more offspring than organisms without these favorable traits

12. Natural Selection • Adaptation – a feature that has become common in a population because the feature provides a selective advantage OR the process by which an organism becomes better suited to its environment • Natural selection causes the spread of an advantageous adaptation

13. Four Major Points of Darwin’s Theory: • There is variation in the genes of every population or species (because of random mutations and translation errors) • In a particular environment, some individuals of a population or species are better suited to survive (because of genetic variation) and have more offspring (natural selection) • Over time, the traits that make certain individuals able to survive and reproduce tend to spread in that population • Evidence from fossils and other sources suggests that species living today evolved from species that are extinct – no longer living

14. Darwin’s Ideas Updated • Knowledge of genetics now helps scientists understand the process of natural selection better; natural selection causes the frequency of certain alleles in a population to increase or decrease over time • Reproductive isolation – when two populations of the same species do not breed with each other because they live in different places; the two species will usually become increasingly different

15. How Fast Does Evolution Happen? • Gradualism – the idea that gradual change over a long period of time is what forms new species • Punctuated equilibrium – a different idea that suggests species go for long periods without changing (or changing very little) and then change quickly

16. Evidence of Evolution • Organisms that evolved from common ancestors should show similarities in some way • Fossils – include any traces of dead organisms (footprints, animal tracks, insects, impressions of leaves or skin, bones, etc.) • Because new species form from existing species, Darwin predicted that transitional forms – intermediate stages between older and newer species would be found in the fossil record

17. More Evidence of Evolution • Comparing the anatomy of different organisms • Comparing the way organisms are put together provides evidence for evolution • Vestigial structures – structures that have become reduced in size because they have no function, they are considered to be evidence of an organism’s evolutionary past • Example: the hind limbs bones of a whale; human tailbones

18. More Evidence of Evolution • Homologous structures – structures that share a common ancestry; they are similar because they are modified versions of structures that occurred in a common ancestor • As a human embryo develops, it shows similarities to all other vertebrate embryos, which has also been used as evidence to support the theory of evolution

19. Homologous Body Structures Turtle Alligator Bird Mammal Ancient lobe-finned fish

20. More Evidence of Evolution • DNA Evidence - DNA and proteins are being analyzed to see how closely related species are to one another • If two species are very closely related, they will share more of the same nucleotide sequences (remember the A, T, C and G?) in their DNA and more of the same resulting amino acid sequences in their proteins (because the DNA sequence determines the order amino acids are put together, which determines the protein)

21. Four Factors in Natural Selection: 1. All populations have genetic variation (2 main sources of this: sexual reproduction and mutations) 2. The environment presents challenges that organisms must overcome in order to successfully reproduce and pass on their genes 3. Individuals tend to produce more offspring than the environment can support, which creates competition for survival (for limited resources like food, water, etc) 4. Individuals that are better able to cope with the challenges presented by their environment tend to leave more offspring than those individuals less suited to the environment

22. Examples of Natural Selection • Antibiotic resistant bacteria (tuberculosis) • The peppered moth and Kettlewell’s experiment: • Until the 1850’s (Industrial Revolution) dark gray peppered moths were rare because the trees where they lived had light colored bark, so the dark moths were more likely to be seen and eaten by birds. After the pollution turned the bark black, the dark moths became more common. In the 1950’s Kettlewell tested this by releasing equal #s of light and dark moths in a polluted forest (dark colored bark on the trees). He recaptured 2/3 more dark moths than light moths. Then he released equal #s in a non-polluted forest (light bark on the trees) and recaptured 2/3 more light moths than dark moths.

23. (Ch. 15) Populations • The Puzzle of Sickle Cell Anemia - People in Africa who are heterozygous for the sickle cell allele are much less susceptible to malaria • Deaths in Africa from sickle cell anemia are about 1 in 100 (1%), while 1 in 5 (20%) individuals are heterozygous for the allele and survive malaria • This means natural selection has favored the sickle cell allele in central Africa because the payoff in survival from malaria (for heterozygotes) is higher than the rate of death from sickle cell anemia (for homozygotes)

24. More Sickle Cell • This is an example of balancing selection – a situation in which an allele remains at the same frequency because the natural selection for an allele is balanced by the rate of selection against it • This means that the number of people dying from sickle cell anemia (which removes some of the homozygous alleles from the population) is balanced by the number of people who survive a malaria infection because they are heterozygotes for the sickle cell allele (and live to pass on the sickle cell allele to their offspring)

25. What About in the U.S.? • In the U.S. the frequency of sickle cell anemia is 1 in 500 (0.2%) for African Americans because malaria is so rare here, which means there is no selective advantage to being a heterozygous individual. There is only the selective disadvantage of being homozygous. This type of unopposed (or one-sided) selection is called directional selection, which moves the frequency of an allele (and its trait) in one direction.

26. How Populations Evolve • Population – all the individuals of a species that live together in one place at one time (can vary in size) • Natural selection changes how frequently genes (alleles) show up in a POPULATION

27. 5 Main Forces That Affect Evolution in Populations • Mutation – changes in the DNA; they are relatively rare so changes in a population because of mutations would happen over very long periods of time • Gene flow – the movement of alleles into or out of a population (because individuals are migrating in or out of the population) • Nonrandom mating – choosing a mate because they live nearby or based on certain traits, such as size, color, ability to gather food or build a nest, etc.

28. 5 Main Forces That Affect Evolution in Populations Continued • Genetic drift – in a small population, the allele frequency can be greatly changed by a chance event, such as a fire, flood or other natural disaster • Natural selection – how often an allele appears in a population depends on how it affects survival and reproduction