Chapter 10: Evolution

Introduction 2 million species on Earth that have been given a scientific name Many more unidentified species: 5 million, 10 million? How many species have gone extinct? Organisms today may represent less than 1% of all life forms that have ever existed How life has changed over time and how we make sense of the living work around is the focus. Understanding the mechanisms by which species evolve by natural selection is one of the most important and influential concepts in biology

Darwin Evidence for Evolution A. Charles Darwin: naturalists that took a 5 year trip around the world on the HMS Beagle in1831 and observed diverse and unique organisms 1. Galapagos Islands: noticed that groups of animals varied from island to island (finches and tortoises) 2. Noticed similarities and differences among animals around the world 3. Darwin took years to put together his evidence for a theory of evolution and his theory forms the basis for modern thoughts on evolution by natural selection Darwin

Giant Tortoises of the Galápagos Islands Section 15-1 Pinta Tower Pinta Island Intermediate shell Marchena James Fernandina Santa Cruz Isabela Santa Fe Hood Island Saddle-backed shell Floreana Hood Isabela Island Dome-shaped shell

Galapagos’s Tortoise Galapagos's tortoise can live for over 150 years Eat plants Different shells depending on the island

Alfred Wallace: another scientist that developed the same idea of evolution in 1858. 1. Darwin and Wallace presented their ideas jointly to the Linnean Society in 1858

What is evolution? 1. Evolution: process of cumulative change in the heritable characteristics of a population a) Heritable: changes must be passed on genetically from one generation to the next: doesn’t happen overnight b) Cumulative: stress the fact that one change is usually not enough to have a major impact on a species c) Population: changes do not affect just one individual Evolution

2. Speciation: new species arises if enough changes occur in a population and they can no longer interbreed Evidence for evolution by natural selection a) Fossil records b) Animal breeding c) Homologous structures d) DNA evidence: some contradictions to evolution but also provided new support for natural selection

4. Modern synthesis or neo-Darwinism: combination of Darwin’s ideas with a newer one, Mendel genetics a) Darwin couldn’t explain how traits were passed down b) Mendel was working on his pea experiments for heredity (1856-1863) c) Darwin never read Mendel’s work d) Not until the 1900’s did the two ideas come together to show how natural selection and heredity worked together

Fossil record and evolution 1. Fossils: petrified remains or traces of animals and plants 2. Fossil record: accumulation of evidence from these remains and traces such as skeletons and footprints 3. Paleontologists have been collecting and classifying fossils in an organized fashion for almost 200 years.

Discoveries that provide evidence for evolution a) Life that existed more than 500 million years ago was vastly different in appearance form life today b) Although Earth has had oceans for most of its existence, fish fossils have only been found in rocks 500 million years old or younger c) Most top predators today are mammals, but not of them existed at the time of dinosaurs or before

d) Majority of living organisms today have no similar form in the fossil record except for sharks, cockroaches, and ferns 5. Conclusion from studying fossils: Life on Earth is constantly changing and changes have occurred over huge timescales (hundreds of thousands or millions of years)

Ageing fossils: Age of a rock can be determined by carefully examining differences in the ratios of isotopes a) Isotopes: versions of atoms that are heavier or lighter than other versions of the same atom (carbon-14 has more mass than carbon-12) b) If a fossil of a bone has a high level of carbon-14, it is younger than a bone that has a very low level of carbon-14

c) Carbon-14 (14C) is radioactive and changes its identity into another atom, nitrogen-14 d) Decay: process of a radioactive parent isotope changing into a stable daughter isotope e) Half-life: time it takes for half of the parent isotope to decay into a stable daughter isotope f) Ratio of radioactive 14C to stable 14N is used to determine the age of a fossil

Artificial selection and evolution 1. Fossil record is incomplete, but breeding domesticated animals provides a good record of change in heritable characteristics 2. Breeders have learned to choose the males and females with the most desirable genetic characteristics and breed them together 3. Artificial selection: human select which animals will reproduce in order to get desired traits

Homologous structures: anatomical structures similar in form but are found in seemingly dissimilar species and show that they had a common ancestor 1. Example: Pentadactyl limbs (penta-five, dactyl- fingers) is found in many diverse animals a) Shape and number of bones may vary, but the general format is the same b) Limb may have very different functions in each animal c) Suggested that all five fingered organism have a common ancestor Homologous

Species divergence: two populations of a species have diverged (separated) and a new species has evolved from an old one 1. Both species will then continue on their separate ways 2. If there is a significant difference in two populations then they can no longer interbreed and are two differed species

Adaptive radiation: occurs when many similar but distinct species evolve relatively rapidly from a single species or from a small number of species 1. Occurs when variations within a population allow certain members to exploit a slightly different niche in a more successful way 2. Niche: position or role within a community of an ecosystem

A new species can evolve by natural selection and the presence of a barrier a) Barrier separating a population could be a mountain range or body of water

Example: Primates found in Madagascar and Comoro Islands off Africa a) Millions of years ago, lemurs were able to grow to large number due to the lack of competition from monkeys or apes b) Large numbers of offspring meant a greater diversity of traits c) Today, there are many different species of lemur with different specialties due to adaptive radiation

i) Some are adapted for living in trees and some on the ground ii) Some are adapted for living in rainforest and others in the desert iii) Most are active during the day (diurnal), but some are nocturnal

d) Lemurs are found today only on these islands, but fossils have been found in Africa, Europe, and Asia e) Lemurs were probably not successfully in competing with apes and monkeys f) Continents and islands tend to either have prosimians (lemurs) or anthropoids (monkeys and apes) but not both types of primates

Example: Finches on the Galapagos Islands a) Probably was one species of finch that evolved into 13 different species of finch b) Different beak shapes allowed them to each different food on different islands

Continuous variation and gradual divergence 1. Figure shows that species A,B,C and D come from a common ancestor, but they are now separate species that could not produce fertile offspring

2. Some species can have various splits over time and create greater diversity between species that no longer resemble each other anymore Within a species that has a wide geographical distribution, there can be measurable difference in DNA a) Climate and soil are different b) Populations adapt to the conditions available and some versions of genes will be selected for and others will be selected against so that the populations are best adapted to their areas (Selective pressure)

c) If the differences between the two c) If the differences between the two separated populations become too great, then they will become separate species

Transient polymorphism Polymorphisms: different versions of a species that can be the result of a mutation 2. Example: Peppered moth (Biston betularia) a) Peppered (grey) form: camouflaged against light surfaces like trees with lichens b) Melanic (black) form: rare mutation 1% of population and easily seen against light colored lichen and are eaten by birds

During the mid 1800’s in the industrial revolution: melanic form increased in number i) Lichen was sensitive to air pollution produced by the industrial revolution and they began to die ii) Air was filled with black soot from burning coal iii) Camouflage of the peppered form of the moth was no longer working since the trees were now darker

Melanic form (carbonaria) had reached 95-100% Today the melanic form doesn’t go above 30% and is often close to 0% due to improvements in air quality since 1956. Transient polymorphism: temporary changes in the form of a species (light moth to dark moth and back to light moth)

Note: Read Theory of Knowledge box on p. 228. Discuss questions.

Natural Selection: mechanism for evolution suggested by Darwin and Wallace A. Natural selection: process by which individuals that are better adapted to their environment survive and reproduce more successfully than less well adapted individuals Natural selection

B. Steps of Darwin’s reasoning for natural selection 1 B. Steps of Darwin’s reasoning for natural selection 1. Overproduction of offspring 2. Natural variation in the population (Genetic variation) 3. Struggle to survive 4. Differential survival: best fit survive better 5. Reproduction

Overproduction: Too many offspring 1. Plants and animals produce more offspring than could ever survive 2. Maximizes the chances of some offspring surviving Struggle to survive: Too many offspring and not enough resources creates competition for these resources

E. Genetic variation 1. Asexually reproducing organisms like bacteria has little chance for DNA modification 2. Sexually reproducing organisms produce slightly different offspring each time which can lead to a wide variety of offspring in a population 3. Variation is closely related to how successful an organism is

a) How frequent an allele is can change over time because of changes in the environment and is possible if there is more than one form of the allele b) When there is a change in the environment, a variation in a species will allow some to survive while others may die c) Variation is strength in a population

In asexually reproducing populations where all members are identical, there are just two outcomes: survival or death a) Great Famine in Ireland was caused by a water mold that infected the potatoes. The potatoes were all produced asexually and were all susceptible to the blight b) More variety leads to more possible outcomes where some survive, some survive with negative effects, some die c) Variety allows some individuals to be better adapted to changes in the environment that may be harmful to others

F. Mechanisms for variation: Mutation, meiosis, sexual reproduction Mutation in DNA a) Disadvantage: mutations can produce genes that lead to disease b) Advantage: beneficial adaptations that allows the organism to survive c) Neutral: effects are neither useful or harmful d) In each generation, only a few genes may mutate

Meiosis: production of 4 haploid gamete cells (egg/sperm) a) Each gamete is genetically different from each other and only contains 50% of the parent cell’s genome b) Produces huge numbers of possible combinations of half the genetic material c) Radom orientation during metaphase I promotes variety in the gametes d) Crossing-over during prophase I further increases the genetic variety Twins

Sexual reproduction: sperm and egg cell must be present at the same moment a) Some chance involved b) Increases variety in the population

G. Adapt 1. Adaptations by natural selection: unconscious changes made by populations and not individuals 2. Fit: organism that has characteristics that are well adapted for its environment 3. Natural selection tends to eliminate from a population individuals that show low fitness and the fittest individuals have higher likelihood of surviving

Example: Giraffe necks

Adaption and survival 1. Evolution is not just based on chance: which individuals survive is determined by their surroundings and the compatibility of their characteristics with those surroundings.

Steps of evolution by natural selection Overproduction of offspring and they have natural variation as a result of genetic differences a) Useful variations allow some to have a better chance of survival b) Harmful variations make it difficult to survive

Individuals with genetic characteristics that are poorly adapted tend to be less successful at obtaining resources and surviving Individuals that are well adapted have a better fitness Individuals that survive to adulthood have a better chance of reproducing and passing on their successful genetic characteristics to the next generation

Over many generations, the accumulation of changes in the heritable characteristics of a population results in evolution: gene pool has changed Darwin called these ideas “ survival of the fittest”

Natural selection and the frequency of characteristics: Modern examples of evolution that have occurred rapidly A. Pesticide resistance in rats 1. Farmer applies pesticide to field to kill the rats 2. Due to natural variation, a few rates are slightly different and are not affected by the poison

3. Resistant rats are better adapted to survive in the presence of the pesticides and now there are fewer rats to compete with for food. They thrive and reproduce, making a new population which some are resistant to the pesticide 4. Farmer puts out more of the original poison and fewer rats die since poison resistance is now favored 5. To kill the resistant rats, a new pesticide must be used

Notes for this example: Resistance is a change that evolves in a population from one generation to the next Immunity develops within the lifetime of an individual and is not the case with the rats. Rat is either born with the susceptibility to be killed by the pesticide or is born with a resistance to it Individual rat cannot adapt and evolve into a resistant rat

5. Characteristics that change and evolve over time must be passed on by genes: Characteristics acquired during an organisms' lifetime cannot be passed on to the next generation and is not a part of natural selection

Antibiotic resistance in bacteria 1. Antibiotics: medications like penicillin that kill or inhibit the growth of bacteria a) Give to patients with bacterial infections b) Does not work on viral diseases

2. Steps of antibiotic resistance in bacteria a) Patient gets a bacterial infection like tuberculosis b) Doctor prescribes antibiotics to kill the bacteria c) Gets better because most of the bacteria are destroyed Due to a genetic modification some bacteria are resistant to the antibiotic Bacteria is not killed and it can now multiply and make the patient sick again Goes back to the doctor for the same antibiotic, but doesn’t get better Doctor has to prescribe a stronger antibiotic and hopes that it works

3. Reasons why the bacteria have developed resistance a) Overuse of antibiotics for nonbacterial diseases b) Not finishing the prescribed amount of antibiotics Resistance

Sources of change in the genetic makeup of bacteria a) Mutations Plasmid transfer: one bacterium donating genetic information to another bacteria by the use of a plasmid (ring of DNA)

Solutions a) Finding new antibiotics b) Minimize use of antibiotics when they are not needed c) Finish the entire course of antibiotics when prescribed

Examples of resistance a) New strains of syphilis: show multiple resistance b) Tuberculosis: resistant to 9 different antibiotics c) MRSA: Methicillin resistant Staphylococcus aureus: staph infection that is often found in hospital settings