2 Evolution Evolution- The process by which organisms have changed (and will continue changing) over time Charles Darwin- Father of Evolution Traveled for 5 years on the H.M.S Beagle mapping the coast of South America, during which he collected specimens and made observations.
3 Darwin s Inspirations Jean-Baptiste Lamarck- Organisms could change over time by selectively using body parts. Organisms can pass these new traits on. (INCORRECT) Charles Lyell- Earth is very old and changes over time Thomas Malthus- If human population continued to increase, there won t be enough space/food. Population will be forced down by war, disease, and famine. **So why do only some individuals survive and/or reproduce?**
4 Darwin s Observations Species vary globally Different, but similar, animal species lived in separate, but similar, habitats around the world. Species vary locally Different, but related, animal species often lived in different habitats within a local area. Species vary over time Some fossils of extinct animals were similar to living species.
5 Darwin s Conclusions Common Descent- Species weren t created in their present form, but rather they evolved from ancestral species. Natural Selection- process by which organisms with variations most suited to their environment survive and leave more offspring; explanation for evolution (change over time)
6 Theory of Natural Selection 1. Struggle of Existence- more individuals are born than can survive; competition for food, space, etc. 2. Variation & Adaptation- populations continue to change as they become better suited for surviving and reproducing, or as their environment changes. 3. Survival of the Fittest- well-adapted individuals survive and reproduce, passing on their adaptations.
7 Natural Selection Grasshoppers can lay more than 200 eggs at a time, but only a small fraction of these offspring survive to reproduce.
8 Natural Selection In this population of grasshoppers, heritable variation includes yellow and green body color. Green color is an adaptation: The green grasshoppers blend into their environment and so are less visible to predators.
9 Natural Selection Because their color serves as a camouflage adaptation, green grasshoppers have higher fitness and so survive and reproduce more often than yellow grasshoppers do.
10 Natural Selection Green grasshoppers become more common than yellow grasshoppers in this population over time because more grasshoppers are born than can survive, individuals vary in color and color is a heritable trait, and green grasshoppers have higher fitness in this particular environment
11 Common Descent Over many generations, adaptation could cause successful species to evolve into new species. All species are descended from common ancestors but have modified/changes over time. Descent with modification
12 Evidence of Evolution-Fossils Earth is about 4.5 billion years old. Fossils- traces of organisms that have been long deceased; can be traced to modern species
13 Evidence of Evolution-Fossils Recently, more than 20 related fossils have been found that document the evolution of modern whales from ancestors that walked on land.
14 Evidence of Evolution-Embryology Early developmental stages of many vertebrates look very similar. This similarity suggests that all vertebrates share a common ancestor.
15 Evidence of Evolution- Homologous Structures Parts of different organisms with similar structures that have adapted for different functions Suggest common ancestry
16 Evidence of Evolution- Analogous Structures Parts of different organisms with similar functions, but different structures.
17 Evidence of Evolution- Vestigial Organs Parts that are inherited from ancestors but have now become unnecessary and non-functional
18 Evidence of Evolution- Genetic Code All living cells use info coded in DNA and RNA to carry info from one generation to the next. Genetic code is nearly identical is almost all organisms à suggests common ancestors
19 Evidence of Evolution- Homologous Molecules Similar proteins between organisms Similar genes- Example: Hox genes
20 Evolution of Populations Population- group of individuals of the same species that live in the same area. Species- a group of populations that can breed and produce fertile offspring Microevolution- small scale changes within a population. Macroevolution- changes in groups larger than a single species over a long period of time.
21 Evolution of Populations- Microevolution Gene Pool- total collection of genes in a population at any one time. Within a gene pool, every allele has a relative frequency (# of occurrences in that population) Evolution is any change in the relative frequency of alleles in the gene pool of a population over time. Natural selection operates on individuals, but resulting changes in allele frequencies show up in populations. Populations, rather than individuals, evolve.
22 Evolution of Populations- Microevolution For example, this diagram shows the gene pool for fur color in a population of mice.
24 1. Mutation Mutations that produce changes in phenotype may or may not affect fitness/survival. Mutations introduce new alleles into a gene pool and change allele frequencies. Mutations only matter in evolution if they can be passed down.
25 2. Migration Gain/loss of alleles from a population due to the movement of individuals or gametes. Individuals who immigrate into a population may introduce new alleles into the gene pool. Individuals who emigrate out of a population may remove alleles.
26 3. Non-Random Mating Individuals may select mates based on heritable traits (size, color). Therefore, some genes will be favored over others. Artificial Selection- selective breeding of organisms by humans for desirable traits (ex. Crops, dogs)
27 4. Genetic Drift Changes in the gene pool of a small population due to chance. Bottleneck effect- resulting from a disaster that reduces population size (volcano). Founder effect- resulting from colonization of new location by small number of individuals.
28 5. Natural Selection If different genes have different fitness, the pressures of natural selection will affect the distribution of phenotypes in population. Directional Selection Stabilizing Selection Disruptive Selection
29 5. Natural Selection Directional Selection- individuals at one end of a distribution curve have higher fitness than others. The range of phenotypes shift because those individuals are more successful at surviving and reproducing. For example, if only large seeds were available, birds with larger beaks would have an easier time feeding and would be more successful in surviving and passing on genes.
30 5. Natural Selection Stabilizing Selection- individuals near the center of the distribution curve have higher fitness than others. This situation keeps the center of the curve at its current position, but narrows the graph. For example, very small and very large babies are less likely to survive than average-sized individuals. The fitness of these smaller or larger babies is therefore lower than that of more average-sized individuals.
31 5. Natural Selection Disruptive Selection- individuals either end of the distribution curve have higher fitness those in the middle. This situation acts against those with an intermediate type and can create two distinct phenotypes. For example, in an area where medium-sized seeds are less common, birds with unusually small or large beaks would have higher fitness. Therefore, the population might split into two groups one with smaller beaks and one with larger beaks.
32 Speciation Factors such as natural selection and genetic drift can change the relative frequencies of alleles in a population, but this alone does not lead to development of a new species. How does speciation happen? Speciation- Formation of a new species from an old species. Mechanisms: Reproductive Isolation Behavioral Isolation Geographic Isolation Temporal Isolation
33 Reproductive Isolation Speciation starts with reproductive isolation, when a population splits into two groups and the two populations no longer interbreed. They may evolve into 2 separate species. This can be caused by behavioral, geographic, or temporal isolation.
34 Behavioral Isolation When two populations that are capable of interbreeding develop differences in courtship rituals or other behaviors. For example, eastern and western meadowlarks are similar birds whose habitats overlap. But they won t mate with each other, partly because they use different mating songs.
35 Geographic Isolation When two populations are physically separated by geographic barriers such as rivers or mountains. For example, the Kaibab squirrel is a subspecies of the Abert s squirrel that formed when a small population became isolated on the north rim of the Grand Canyon. Separate gene pools formed, and genetic changes in one group were not passed on to the other.
36 Temporal Isolation When breeding occurs at different times for different species. For example, 3 species of orchid live in the same rain forest. Each species has flowers that last only one day and must be pollinated on that day to produce seeds. Because the species bloom on different days, they cannot pollinate each other.
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