Evolution & Natural Selection

Carl Sagan’s Universe Calendar 24 days = 1 billion years 1 second = 475 years http://www.youtube.com/watch?v=g2qezQzfgIY

Early Thoeries Linnaeus (1707–1778) developed the first comprehensive and still influential classification and taxonomy of plants and animals. Fossil discoveries during the 18th and 19th centuries raised doubts about creationism.

Before Darwin Geologists and paleontologists had made a compelling case that: Uniformitarianism: the assumption that the natural processes operating in the past are the same as those that can be observed operating in the present. life had been on Earth for a long time. it had changed over that time and many species had become extinct. Charles Lyell 1797 - 1875

Influences on the Theory Thomas Malthus published a book in 1797 called Essay on the Principle of Population in which he warned his fellow Englishmen that most policies designed to help the poor were doomed because of the relentless pressure of population growth. A nation could easily double its population in a few decades, leading to famine and misery for all. Species cannot reproduce to their full potential because there is struggle for existence. In this struggle for existence, survival and reproduction do not come down to pure chance. Some traits help produce more offspring.

Theories of Evolution Darwin and Wallace, 1850s Natural selection is the process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common, due to differential reproduction of genotypes. On the origin of species, 1859 Charles Darwin http://www.youtube.com/watch?v=910dz5sCb1I&feature=related

Darwin’s Travels

Selective (artificial) Breeding This Chihuahua mix and Great Dane show the wide range of dog breed sizes created using artificial selection. http://www.dailymotion.com/video/x4yjed_the-story-of-oliver-the-humanzee_animals

Evolution vs. Natural Selection Charles Darwin Evolution & Natural Selection Evolution: Is the process of change in the inherited traits of a population of organisms from one generation to the next (processed at the level of the genes). Natural Selection: Is the process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms and unfavorable heritable traits become less common, due to differential reproduction of genotypes. Charles Robert Darwin 1809 - 1882

Principles of Natural Selection There is variation in traits: For example; some beetles are green & some are brown. There is differential reproduction: - Environments cannot support unlimited population growth (Malthus) – Not all individuals get to reproduce to their full potential. There is heredity - Traits have a genetic basis. The more advantageous traits allow more offspring. If you have variation, differential reproduction, and heredity, you will have evolution by natural selection.

Mendel’s Experiments Austrian monk Gregor Mendel began a series of experiments that revealed the basic principle of genetics in 1856 Studied inheritance of seven contrasting traits in pea plants Discovered that heredity is determined by discrete particles or units Gregor Mendel 1822 - 1884

Double Helix Chromosome: a paired length of DNA, composed of multiple genes. Gene: a place (locus) on a chromosome that determines a particular trait. Allele: a variant to a particular gene.

Gene pairs Heterozygous: dissimilar alleles of a gene in an offspring. Homozygous: two identical alleles of a gene in an offspring Dominance produces a distinction between genotype (hereditary makeup) and phenotype (expressed physical characteristics)

Forces of evolution Genetic Drift Mutation

Genetic Drift Genetic drift is one of the basic mechanisms of evolution. There is no direction or selection in genetic drift, it is simply about luck. If an individual leaves more offspring simply by chance, that is genetic drift. Genetic drift depends strongly on small population size since the law of large numbers predicts weak effects of random sampling with large populations. By definition, genetic drift has no preferred direction

Mutations In biology, mutations are changes to the nucleotide sequence of the genetic material of an organism. Mutations can be caused by copying errors in the genetic material during cell division. Mutations create variation within the gene pool. Less favorable (or deleterious) mutations can be reduced in frequency in the gene pool by natural selection, while more favorable (beneficial or advantageous) mutations may accumulate and result in adaptive evolutionary changes.

What Is Adaptation? Adaptation: Any change in the structure or functioning of an organism that makes it better suited to its environment. This process leads to changes in the organisms and impacts their environment. The human species adapts biologically and culturally. There are things that are not adaptations, for example, blood is red, not because it’s an adaptation, but because of it’s chemical make up.

What Is Not an Adaptation? Eye Lots of things: One example is vestigial structures. A vestigial structure is a feature that was an adaptation for the organism’s ancestor, but that evolved to be non-functional because the organism’s environment changed.

Adaptation Vs. Acclimatization Adaptation: Anything that helps an organism survive in its environment which usually occurs over several generations. Acclimatization: The short-term process of adjusting to changes in an environment such as shivering for temperature regulation or increasing red blood cell counts to acclimatize to high altitudes. Usually occurs in one lifetime.

Human Adaptations to High Altitude Bolivians in the highlands use increased hemoglobin production, which carries more oxygen in the blood to adapt to the low levels of oxygen at high altitudes, while inhabitants of the Tibetan plateau use increased respiration. Three High-Altitude Peoples, Three Adaptations to Thin Air; National Geographic News. http://news.nationalgeographic.com/news/2004/02/0224_040225_evolution.html

Sickle cell anemia, malaria & adaptation People who have sickle cell anemia, a serious hereditary blood disease, are more likely to survive malaria, a disease which kills some 1.2 million people every year. What is puzzling is why sickle cell anemia is so prevalent in some African populations. Red blood cells, containing some abnormal hemoglobin, tend to sickle when they are infected by the malaria parasite. Those infected cells flow through the spleen, which culls them out because of their sickle shape -- and the parasite is eliminated along with them. http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html

Why we don’t all look alike Bergmann’s Rule: Within a species the body mass increases with latitude and colder climate (i.e., larger sub-species are found at higher altitudes or colder climates. Allen’s Rule: In warm blooded species, the relative size of the limbs of the body decreases with decreases of mean temperature. Gloger’s Rule: within a species more heavily pigmented forms tend to be found in more humid environments (e.g., near the equator: most studied in birds). Caveats: Tibetans (high UV radiation); Inuits (diet high in vitamin D).