Chapter 17 – Evolution Lecture Notes PDF

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Chapter 17 – Evolution Biological Evolution -

Refers to the gradual change of populations or organisms over generations (still occurring today). Changes over the lifetime of one individual is not evolution (ex. aging process or changing of behaviour).

History of Evolution Theory -

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Natural history is the study of organismal form and variety in natural environments. Aristotle (about 300 B.C) was the first to begin classifying organisms, suggesting they had fixed characteristics. Aristotle’s observation was merged with biblical accounts, bringing in the idea of a higher being – natural theology. The ladder-like classification that begins with simple, non-living beings at the bottom, and complex beings at the top, with God being the highest is known as the Scala Naturae (natural scale). Taxonomy was established by Linnaeus (1700s) and refers to the biological classification of organisms (based on characteristics – still use a modified version today).

Three New Disciplines -

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Three disciplines that contributed to the history of evolutionary theory (about 1600s): 1. Biogeography 2. Comparative morphology 3. Geology All promoted awareness of change – people used to believe that things did not change, and that God created everyone ideally for their environment.

(1) Biogeography -

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Refers to the world distribution of organisms. Raised questions regarding how the changes in Earth’s geography relates to species distribution, environmental impacts that will cause organisms to change, if there was a limit to the number of species created by God, etc. Global exploration raised difficult questions for “unchanged creation”.

(2) Comparative Morphology -

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It was observed that appendages of certain species had similar locations, were made of the same materials, and developed similarly. However, they differed in size, shape, and function. This raised the question of why the Creator didn’t use different materials. Natural theologians proposed that the body plans were perfect, and there was no need to create a new one for each species. Currently useless (vestigial) structures exist (ex. pig’s feet have two useless toes). Therefore, characteristics have changed since creation. Buffon Leclerc (1700s) proposed that characteristics are conceived by nature (God) and changed by time.

(3) Geology -

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Georges Cuvier (1769-1832) realized that layers of fossils represented organisms that lived at sequential times in the past. Stratification refers to the horizontal layering of sedimentary rocks He proposed the idea of catastrophism: theory that fossils suggested extinction from a catastrophic event. Each fossil layer represents organisms that died in a local catastrophe.

Changes in Earth -

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Hutton (1700s) argued that slow and continuous physical changes over long periods of time caused Earth’s geological features – gradualism (correct theory). This challenges biblical theories since it suggests that Earth is older than the bible suggests it to be. Lyell (1800s) suggested that the geological processes that sculpted the Earth in the past (volcanic eruptions, earthquakes, etc.) are the same today – uniformitarianism. Earth is constantly changing.

Jean Baptiste de Lamarck (1744-1829) -

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Proposed the first theory of evolution: simple organisms evolve into more complex ones by a perfecting principle. Note: it was not Darwin who proposed the first theory. He was the first to get it right, however. Based on two mechanisms: 1. Principle of use and disuse – the more a structure is used, the more perfect it becomes. 2. Inheritance of acquired characteristics – “perfection” will be inherited by offspring. These mechanisms were incorrect. If someone works out a lot and perfects their muscles, Lamarck proposed that the offspring would be born with large muscles. Major contributions to evolutionary thought: 1. Species change with time. 2. Changes are inherited. 3. Organisms respond to environment. 4. Mechanisms that cause evolutionary changes exist. All fostered the discussion of change.

Charles Darwin (1809-1882) -

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Father of evolutionary biology. Englishman who was born to a fairly wealthy and educated family with professions in the medical field. He enrolled in medical school, but dropped out and became a clergyman instead. He was also a voyager. The naturalist on the ship left due to illness, so Darwin took over his role, and made observations about world around him. This planted the seed for theories of evolution. His 1831 voyage on the H.M.S. Beagle (had three major fields at this time) was during the time of modern geology – three major fields were relevant. Applied gradualism and uniformitarianism to the living world.

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He observed global biogeography and noticed that: o Fossils are similar to extant (living) organisms. o Organisms near each other are similar even if they are in different habitats (ex. similarities between island and non-island organisms). o Species change after isolation from ancestral groups. o Organisms today are descendants with modifications (he doesn’t know how it actually happens yet – no “mechanism”). Examined species such as the Galapagos tortoise, marine iguana, and blue-footed booby (males have blue feet to attract mates – courtship display). Darwin developed the term artificial selection, which refers to selectively breeding organisms with favourable characteristic – humans select the characters that they want. Natural selection refers to the process by which characteristics that better enable organisms to adapt to specific environmental pressures will tend to increase in succeeding generations in a population. Darwin read an essay about population limits and applied it to his own work. The struggle for existence occurs when resources limit reproductive of organisms. He noticed that all species produce more offspring needed to replace parent generation but we are not overcrowded. Some survive and reproduce, and some don’t. Those who have the characteristics to get resources survive, and those who don’t will die (money in today’s society). Adaptive traits are genetic characteristics that increase likelihood of survival and reproduction. These traits, over time, are what increase in a population.

Darwin’s Impact -

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Darwin argued that all organisms arise through descent with modification, the evolutionary alteration and diversification of ancestral species. o Natural selection drives evolution o Only limitation was no theory of heredity He envisioned descent with modification as a tree: o Main trunk is ancestor of all organisms and branches are evolutionary divergence of ancestors – known as the Tree of Life. Darwin’s theory was distinguished from earlier explanations: 1. He provided purely physical rather than spiritual explanations for origins of life. 2. He recognized that evolutionary change occurs in groups rather than individuals. 3. He described evolution as a multistage process. 4. He understood that evolution occurs because some organisms function better than others in a particular environment. Humans were not initially mentioned in The Origin. After a later publication, people became angered by the fact that Darwin’s theory suggested a common lineage between humans and apes. Darwin did not understand genes and chromosomes and patterns of inheritance yet.

Alfred Wallace -

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Scientist studying the changes of species over time. He wrote an essay on this theory of evolution and sent it to Darwin. The two presented their work together, but since Darwin’s work was more complex, his was published first (The Origin of Species by Means of Natural Selection). Important player in history of the study of evolution.

Evolutionary Biology Since Darwin The Modern Synthesis -

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Refers to the unified theory of evolution, and integrates biogeography, comparative morphology and embryology (how organisms begin to develop after fertilization), genetics (molecular techniques), paleontology and taxonomy within an evolutionary framework. Links microevolution and macroevolution: o Microevolution refers to small-scale genetic changes within a population, often in response to changes in the environment (ex. Ontario). o Macroevolution refers to large-scale genetic changes within an entire species as a result of gradual accumulation of microevolutionary change (ex. Earth).

Evidence for Biological Evolution 1. Adaptation is the product of natural selection: o Ex. the wings of birds have an obvious function that helps these animals survive and reproduce. 2. The fossil record: o Darwin’s theory suggests that all species that have ever lived are genetically related. The fossil record documents this continuity in morphological characteristics, providing evidence of changes in biological lineages. o Ex. evolution of modern birds can be traced from a dinosaur ancestor through fossils. 3. Historical biogeography: o The study of geographical distributions of organisms in relation to their evolutionary history is generally consistent with Darwin’s theory of evolution. o Ex. oceanic species resemble species on the mainland, suggesting a common ancestry. o Ex. South American monkeys differ from African monkeys and have a different common ancestor. 4. Comparative morphology: o Analyses of the structure of organisms are based on the comparison of homologous traits, characteristics that are similar in two different species because they inherited the genetic basis it from the same ancestor. o Ex. the forelimbs of tetrapods (humans, dogs, cats, etc.) are homologous because they evolved from a common ancestor. Molecular Techniques -

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Old molecular techniques involved comparing embryos and patterns of development. Embryogenesis is highly conserved, and early embryos of related species are often similar, although adult structures may differ. Modern molecular techniques look at the genetic basis for ancestry and modification (nucleotides).

Snake’s Limbs -

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Discovered using modern molecular techniques. One slight change in genes early on can create a major change later on. Two genes are involved: Hoxc6 and Hoxc8. Homeotic genes (regulate development of anatomical structures) code for transcription factor (protein that regulates gene expression). When you have regions where both genes are expressed, that part of the body will form ribs. In areas where only Hoxc6 is expressed, forelimbs will be expressed just above this area. In the snake, there has been a mutation in the Hoxc8 gene, causing it to be expressed in the forward region of the body. This prevents forelimbs from forming. Note: hind limbs are controlled by another set of genes.

Variation and Selection -

Darwin observed that individuals exhibit variation in many characteristics. Natural selection acts at that individual level. Inherited characteristics enhance survival and reproduction. These individuals have enhanced relative fitness and are better adapted to their environment. Note: not all traits are adaptive.

Convergent Evolution -

Refers to similar adaptations in related organisms due to similar selective pressures. Ex. wings of insects, bats, and birds are not homologous. They lived in similar types of environments, so they all developed wings. There is no common ancestor.

Sexual Selection -

A type of natural selection that involves variation in reproductive success that is influenced by sexually dimorphic characters (differences between males and females). Ex. variations in phenotypes, morphology, behaviour, and pheromones. Males have to attract females, not vice versa. Males show their characteristics to promote health, resources, and ability to reproduce....