How Did Life Begin?

1. How Did Life Begin? When Earth formed, about 4.5 billion years ago, it was a fiery ball of molten rock. Eventually, the planet’s surface cooled and formed a rocky crust. Water vapor in the atmosphere condensed to form oceans. Most scientists think life first evolved in these oceans and that evolution occurred over hundreds of millions years.

2. How Did Life Begin? 1. The “Primordial Soup” Model 2. Miller-Urey Model 3. Bubble Model

3. 1.“Primordial Soup” Model • In the 1920’s, a Russian scientist named Oparin and a British scientist named Haldane, hypothesized that early oceans on Earth contained large amount of organic molecules, • like soup is filled with many different ingredients • Oparin and Haldane hypothesized that these organic molecules formed spontaneously in chemical reactions activated by energy from solarradiation, volcanic eruptions and lighting

4. “Primordial Soup” Model Continued Oparin and an American scientist, Harold Urey, proposed that the Earth’s atmosphere lacked oxygen. They hypothesized that the early atmosphere was instead composed of : - Nitrogen gas - Hydrogen gas - Hydrogen-containing water vapor - Ammonia - Methane

5. Without oxygen, high energy electrons in these gases would be free to react with hydrogen-rich molecules to form a variety of organic molecules. 2. Miller-Urey Model In 1953, the “Primordial Soup” Model was tested by Stanley Miller, who was working with Urey at the time.

6. They put these gases that they proposed had existed on Earth into a device. They simulated lightingby providing electrical sparks. After a few days, they found a collection of organic molecules which included some of the building blocks of life: • - AA • - FA • other hydrocarbons (molecules made up of hydrogen and carbon) • These results supported the hypothesis that some basic chemicals of life could be formed spontaneously under conditions like those in the experiment

7. The Bubble Model • In 1986, Louis Lerman suggested that the key processes that formed the chemicals needed for life took place within bubbles on the surface of the ocean • Lerman’s Hypothesis: • 1. Ammonia, methane and other gases resulting from many eruptions from undersea volcanoes were trapped in underwater bubbles

8. Chemical reactions would take place faster in bubbles where all the reactants would be found in concentrated amounts. • Bubbles rose to the surface and burst, releasing simple organic molecules into the air • Now the organic molecules were exposed to UV radiation and lighting, which provided energy for further reactions. • Now more complex organic molecules that were formed fell into the ocean with rain, starting another cycle.

9. Therefore, the molecules of life could have appeared more quickly than could be accounted for by the “Primordial Soup” model alone.

10. Evolution Part 1: Natural Selection Charles Darwin

11. Charles Darwin1809-1882 • The Father of Evolution • Born in 1809, England • Sailed on the HMS Beagle • During his voyage, he made observations that led him to his theory ofevolution

12. This voyage lasted from1831 to 1836.

13. Many of Darwin’s conclusions were based on observations of wildlife in theGalapagos Islands. The Galapagos Islands lie 500 miles west of Ecuador in the Pacific Ocean, directly on the equator. “Galapagos” means turtle.

14. Galapagos finches Among other things, Darwin noticed there were several types of finches on these islands. In particular, Darwin observed something odd about the finches: they all looked like a bird he had seen on theSouth American continent.

15. The most distinct difference among finch species is theirbeaks, which are adapted for the specific diets available on the islands.

16. Darwin hypothesized that some of the birds from South America migrated to the Galapagos. Once on the islands, the birds must have changedover the years. This would explain the many different species of birds present.

17. G. fortis G. fuliginosa Camarhynchus pauper Cactospiza pallida G. magnirostris C. psittacula G. scandens C. heliobates C. pauper G. conirostris Geospiza difficilis Platyspiza crassitrostris Certhidea olivacea & C. Fusca Cacts Finch (nectar,eeds, blood) Woodpecker-like Finch (seeds & insects) Insect-eating Finch Seed-eating Finch Vegetarian Finch Ground Finch Tree Finch Warbler Finch PHYLOGENETIC TREE: A diagram showing the evolutionary history of a speciesof an animal. The common ancestor is at the bottom. This tree has how many major branches? “Original” Finch

18. Darwin called this… After returning from the Galapagos and studying all the different types of plants & animals he collected during the voyage, Darwin concluded that organisms change over time…. evolution which means change in species over time Darwin called the mechanism for evolution… Natural Selection

19. Natural Selection a.k.a.Survival of the Fittest. Those individuals that are better fit for their environment have a greater chance to survive and mate to reproduce. Therefore, their genetic traits become more common or frequent over time. The genetic traits of less fit individuals become less common or frequent over time.

20. The key that unlocked Darwin’s thinking about how evolution occurs was an essay written in 1798 by an English economist named Thomas Malthus. Malthus wrote that human populations are unable to increase faster than the food supply can. He suggested that human populations do not grow unchecked because of death caused by disease, war and famine will slow population growth.

21. In Darwin’s Time, most scientists believed that each species remained unchanged in the form that it was originally created. Scientists then started to try to find explanations for the origins of fossils…….. In 1809, the French Scientist named Jean Baptiste Lamarck proposed a hypothesis for how organisms change over generations. He believed that over the lifetime of an organism, physical featureswould increase or decrease in size because of either the use or disuse of the feature. According to Lamarck, these changes would then be passed on to offspring.

22. Lamarck had correctly identified that a change is a species is linked to an organism’s environmental condition.

23. The recipe for Natural Selection

24. Every species is different, even within itself. 1. All species have genetic variation. Example: some beetles (of the same species) are green and some are brown http://evolution.berkeley.edu/evolibrary/

25. 2. The environment presents challenges to survival. Example: green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do. http://evolution.berkeley.edu/evolibrary/ • There is a constant struggle for survival. • Examples are: • Natural disasters like droughts, fires, floods, etc. • Competition for resources like • food, space, or mates • Other dangers like • predation, disease, or parasitism WHY would green beetles get eaten more often than brown beetles?

26. Individuals that are fit* to their environment leave more offspring than those who aren’t. Example: The surviving brown beetles have brown baby beetles because this trait has a genetic basis. http://evolution.berkeley.edu/evolibrary/ *Fit or fitness – does not mean “buff” beetles; more fit means they are better adapted or more likely to survive; they’re a good “fit” for their environment…

27. Therefore, characteristics of fit individuals increase in a population over time. Conversely, over time, genes for less favored characteristics (green colored beetles) will become less common, but not eliminated (because they’re preserved in the heterozygotes) Example: Brown coloration allows the beetle to have more offspring and becomes more common in the population. If this process continues, eventually almost all individuals in the population will be brown. (What would happen if a parasite prefers brown beetles, or if the environment was covered in green leaves?) http://evolution.berkeley.edu/evolibrary/

28. Therefore Darwin’s contributions: Provided evidence that species evolve: In 1859, he proposed the theory of natural selection to explain evolution (survival of the fittest) - Over time, change within a population leads to the replacement of old species by new species as traits that are not selected for become less common. - Some evidence from fossils supports the theory that species on Earth have evolved from ancestral forms that are extinct. (species that have disappeared permanently.)

29. Evolution Part 2:Speciation and Hardy-Weinberg

30. What is a species? A species is one or more populations of individuals that can interbreed, producing fertile offspring. Speciation is the process by which new species are formed over time. Or, why are these two owls different species, but these dogs aren’t?

31. How does speciation occur? Let’s begin with a simple example -- geographic isolation. This is when populations of individuals are geographically separated and prevented from mating with one another. For example, this can be due to the formation of new mountains, canyons, rivers, or other landforms.

32. How does speciation occur? Over time, natural selection, acting on random mutations in the population, makes the DNA so different that the populations are no longer able to reproduce with each other Their chromosomes may not even match up. Once there is no gene flow between the populations, mutations start to accumulate differently in each population and the populations diverge into different species. This is called macroevolution – change on a grand scale including extinction and speciation.

33. Sometimes population ranges of different species overlap, but they still won’t interbreed. Here are some reasons why: • Physical incompatibility • For obvious reasons, crickets can’t mate with giraffes, for example. They just don’t have a common enough ancestor. • Different mating schedules or locations • For example, certain flowers and insects may prefer to mate at different times of day, may bloom at different times of the year, or may prefer different mating locations. So even if they are not geographically separated, they still won’t mate with someone with a different schedule. • Behavior • Animals, especially, are picky. Some have elaborate mating rituals or specific traits they look for in a mate. For example, in some spiders and mantises, if the rituals aren’t pleasing to the female, she will eat the male.

34. Natural selection acts on individuals; Evolution (the change) is measured in populations. Microevolution is defined as the change in allele frequencies* in a population over generations. *Frequency– how often something occurs expressed as a decimal; for example, if something occurs 50 out of 100 times, it has a frequency of 0.5 Changes in gene frequencies are the definition of microevolution.

35. Hardy-Weinberg In 1908, 2 scientists independently came up with a mathematical way to measure if a population is evolving by measuring changes in allele frequencies. • The equation assumes the following conditions: • Very large population • No migration • No net mutations • Random mating • No natural selection • (if the above are occurring the population is most likely NOT going to evolve)

36. What causes genetic change in a population? Those conditions are never fully met. Therefore, the 4 main factors that cause change of allele frequencies in a population are: • Natural selection • Genetic drift • Gene flow • Mutation • Of these, only natural selection adapts a population to its environment, and we’ve already talked about it. The other three may be good or it can be bad for a population

37. Genetic Drift Genetic drift is change in allele frequency due to sampling error (chance) This factor is more pronounced when the population is smaller than when the population is bigger. Two examples: Bottleneck effect – occurs when a population is drastically reduced in size due to a natural disaster such as hurricane or disease, and many alleles are lost completely while others are over or under represented from what they were in the large population; (ex: cheetahs; population is at risk due to a lack of genetic variability Founder effect – occurs when a few individuals from a large population found (start) a new, isolated population ( ex: insects blown from the mainland to an island; humans moving from one continent to another and marrying within their own isolated community, such as the Amish in the U.S.

38. Gene flow Another word for gene flow is migration. Gene flow is when the allele frequency of a population is alteredby individuals moving into (or out of) a population.

39. Mutation As we have studied in past units, a mutation is a change in your DNA. This is the other factor that can change allele frequencies. A flower population with only blue alleles can sometimes produce a red flower due to mutation. That then changes the allele frequency. In general, only things you were born with can be inherited. Things that change your appearance but are not genetic, such as tattoos or ear gauges, cannot be inherited. Even most mutations in your DNA cannot be inherited by your offspring. Think about why. What’s the big exception?

40. Evolution Part 3: Evidence of Evolution

41. Scientific Evidence of Evolution includes: 1. Fossil Records 2. Biogeography 3. Homologies

42. Fossil Record In order for fossils to form: • Calcium must be replaced by harder minerals • Burial must occur by sediments deposited in swamps, mud, ocean floors, tar pits, areas near volcanoes that spew out volcanic ash, etc. Body of the organism must decay slowly. For ex., an animal with a hard exoskeleton (crab) would have a better chance of becoming fossilized than a soft-bodied organism (worm) Fossils are how we know that extinct animals used to live here on Earth.

43. Equus, the modern horse, evolved from the dog-sized Hyracotherium. Notice it evolved from a four-toed front foot to the one-toed front foot of the modern horse. Gradualism says that this happened gradually over millions of years. The evolution of the horse is an example of gradualism. Evidence for gradualism is found in fossil records.

44. What else changed over time according to the diagram (and the fossil record)? Size of the teeth increased. Why? Earth was changing and becoming dryer; grasses were evolving and becoming the primary food source, requiring greater grinding surface. Height increasedas being able to see predators over the grass was an advantage. Running on one toe increased the number of joints andtherefore, the speed of the animal to run from predators. A hoof instead of a soft pad on the foot provided protection from hard ground and coarse grass

46. Punctuated Equilibrium says that these species existed in long periods of stasis (same) interrupted by brief periods of genetic instability that produced changes. This overall change still happened over millions of years. Evidence for this theory is observed in the fossil records

47. Biogeography Is the study of the geographic distribution of species and fossils. It is used to test predictions about the nature, age, and location of certain fossils. . This is what first suggested evolution to Darwin. Species tend to be more closely related to other species from the same area than to other species with the same way of life but living in different areas.

48. Homologies • Characteristics that are shared by related species because they have been inherited in some way from a common ancestor. • There are 3 main categories of homologies: • Anatomical – includes: • (a) homologous structures • (b) analogous structures • (c) vestigial structures • 2. Biochemical • 3. Developmental .

49. 1. Anatomical Homologies (a) Homologous structures have the same underlying structure, but may have evolved different functions. . • For example, the bones on the front fins of a whale are homologous to the bones in a human arm and both are homologous to the bones in a bat wing and cat leg.

50. All homologous structures have evolved from a common ancestral structure but now these structures are used to do different tasks for each organism