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Charles Darwin and Natural Selection Darwin journeyed on the HMS Beagle as a naturalist • • • • • 5 year journey studied and collected many biological specimens on Galapagos Islands, off coast of Ecuador, observed animals such as finches, tortoises, and iguanas Thirteen different but similar species of finches, each with a distinctive bill that is specialized for a particular food source. Suggested that these birds migrated from Ecuador and changed after they arrived. Darwin’s ideas were influenced by: • Jean Baptiste Lamarck, who hypothesized that acquired traits were passed onto offspring •Charles Lyell, a geologist, who suggested that the Earth was much older than 6000 yrs •Thomas Malthus, who wrote that human populations grow much faster than their food supply •Alfred Wallace, who suggested natural selection after studying wildlife in the Malay Archipelago. Darwin observed differences among island species. Marine iguana Land iguana Thirteen different but similar species of finches, each with a distinctive bill that is specialized for a particular food. Suggested that these birds migrated from South America and changed after they arrived Key insights led to Darwin’s idea for natural selection. • Darwin noticed a lot of variation in domesticated plants and animals. • Artificial selection is the process by which humans select traits through breeding. • Heritability is the ability of a trait to be passed down. • There is a struggle for survival due to overpopulation and limited resources. • Darwin proposed that adaptations arose over many generations. • Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals. Principles of Natural Selection 1. Variation. What can cause variation in a population? • Genetic differences and mutation 2. Overproduction. What are pros and cons of overproduction? • Having many offspring increases the chance for survival, but also results in competition for resources. 3. Adaptation. What determines whether an adaptation is beneficial or not? • A certain variation that allows an individual to survive better than other individuals it competes against. 4. Descent with Modification. How does natural selection change a population over time? • Over time, more members of the species will have adaptations that are well suited for survival and reproduction in an environment. Elephants in Queen Elizabeth National Park, Uganda, Africa Normally, nearly all African elephants, male and female, have tusks. In 1930, only one percent of the elephant population in Queen Elizabeth Park was tuskless because of a rare genetic mutation. Food was plentiful, and by 1963 there were 3,500 elephants in the park. In the 1970’s, a civil war began in Uganda. Much of the wildlife was killed for food, and poachers killed elephants for their ivory tusks. By 1992, the elephant population had dropped to about 200. But by 1998, the population had increased to 1,200. A survey revealed that as many as 30 percent of the adult elephants did not have tusks. Ugandan wildlife officials also noted a decline in poaching. Natural selection acts on distributions of traits. • A normal distribution graphs as a bell-shaped curve. • Populations have a normal distribution when they are not undergoing natural selection • Microevolution is evolution within a population. – observable change in the allele frequencies – can result from natural selection Directional selection – favors one of the extreme variations • Woodpeckers with long beaks capture the most insects, as they can reach the insects deep in the tree trunk. • Stabilizing selection – favors the average • Small spiders have a hard time capturing prey • Large spiders easily spotted by birds • Medium sized spiders are best suited to survive in their environment, reproduce more often, leave more offspring. Disruptive selection - favors both extremes • On light colored rocks, the light limpets are camouflaged and survive the best • On dark rocks, the dark limpets are most successful • Tan (intermediate) limpets are visible on both the light rocks and dark rocks, and their numbers decline due to predation Evidence of Evolution A. Fossils Fossil links found between • fish and amphibians • reptiles and birds • reptiles and mammals Whales from land mammals Fossil linking fish and amphibians • 365 million years old • arm bone with fish fin characteristics • found in Pennsylvania • thought to be from a lobed-finned fish Archaeopteryx – links reptiles and birds A fossil of Archaeopteryx was discovered at about the same time Darwin published On the Origin of Species. This pigeon-size creature had a dinosaur like shape, complete with a long bony tail, heavy jaws with serrated teeth, and three long fingers. It also had feathers like those of modern birds. Hind leg bones in whales An amphibious reptile found in Texas, 2005 Diarthognathus, an animal with reptile and mammal characteristics Early mammals may have looked like this Evolution of the horse B. Biological Molecules • Differences in amino acid sequences and DNA are greater between species that are distantly related than between species that are closely related • phylogenetic trees show how organisms are related through evolution Homeobox genes C. Homologous structures – similar in structure, with different functions D. Vestigial Structures • Structures that are reduced in size and either have no use or a less important use than they do in other, related organisms. • Examples: wings on flightless birds, Human ear muscles, human wisdom teeth human appendix , hind leg bones in whales The cassowary, a flightless bird with wings Wisdom teeth in human Human appendix E. Vertebrate Embryos • Early in development, vertebrate embryos have similar characteristics such as a tail, buds that become limbs, and pharyngeal pouches that hold the gills of fish and amphibians. Vertebrate embryos Examples of Evolution A. Tuskless elephants becoming more common in Africa B. Antibiotic resistance in bacteria such as those that cause pneumonia and tuberculosis C. Pesticide resistance in insects • Tobacco plants are sprayed with pesticides • The pesticides kill many insects, but not all. • Survivors lay eggs • Future generations are resistant D. Industrial Melanism • Example is the peppered moth. • Explained by the concealment hypothesis. • Peppered Moth Simulation E. Beaks of finches • Adaptation • the changing of a species that results in its being better suited to its environment. • Examples: camouflage, mimicry, echolocation, migration, dormancy Camouflage Mimicry: one species resembles another Snake mimicry: which is harmful? Eastern Coral snake Highly venomous King snake Non-venomous Echolocation in bats. Hibernation Migration Dormancy: cacti embryos coming out of dormancy Patterns of Evolution A. Divergence – Darwin’s finches. Dogs evolving from wolves. Can lead to formation of new species (speciation) B. Convergent evolution • distantly related organisms evolve similar traits. • Example is seen in the streamlined, finned bodies of dolphins and sharks. • The fins would be an example of analogous structures. Five Evolutionary forces 1. Natural Selection: certain traits might be an advantage for survival 2. Mutation: creates new genetic variation 3. Sexual selection: certain traits may improve mating success; alleles for these traits increase in frequency 4. Gene flow: movement of individuals to or from a population (also known as migration). Immigrants add alleles, emigrants take alleles away. Example: troops of baboons in eastern Africa. Females remain with the troop, but younger or less dominant males leave their birth troop, eventually joining another troop. This ensures gene flow. 5. Genetic drift: random change in allele frequency in a population. Causes a loss in diversity. Example: In the 1800’s, northern elephant seals were overhunted. The population was reduced to about 20 individuals. Hunting has ended, and there are now about 100,000 seals. However, the population has little genetic variation. Genetic drift Fitness the genetic contribution of an individual to the next generation's gene pool relative to the average for the population, usually measured by the number of offspring that survive to reproductive age Microevolution • a change in gene frequency in a population — such as all the individuals of one beetle species living on a particular mountaintop. Macroevolution • generally refers to evolution above the species level Evolution of whales from landdwelling mammals Evidence • transitional fossils between land mammals and whales • vestigial structures such as pelvic and leg bones, and external ear muscles • nostrils at end of snout in embryos; nostrils travel to top of head before birth • DNA for milk protein very similar in hippos and whales