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Transcript
Descent with Modification: A Darwinian View of Life Lesson 7.1 Ch. 22 Charles Darwin and TOS • Published on Nov. 24, 1859 • Two major points: – Species of organisms on earth today are descendents of ancestral species that were different from the modern species. – Mechanism for this evolutionary process – natural selection Natural Selection • A population can change over generations if individuals that possess certain heritable traits leave more offspring than other individuals • Result of natural selection – evolutionary adaptation (an accumulation of inherited characteristics that enhance organisms’ ability to survive and reproduce in specific environments. • Evolution – change over time in the genetic composition of a population The Evolution Revolution • Darwin’s (1859) publication flew in the face of both modern culture AND modern science – It was not readily accepted by the scientific community either • Oldest cultural influence on origins: Genesis – Each species created perfectly and individually by God • Aristotle (384-322 B.C.) gave Western culture the first view of the organization of life outside of religion – Scala naturae - ladder of increasing complexity – each organism had a permanent spot on the ladder The Evolution Revolution • Carolus Linnaeus (1707 – 1778) – founder of taxonomy (naming and organizing species) – Binomial nomenclature – Argued that resemblance among species pointed to the order and pattern in which they were created – Darwin later used this to develop his evolutionary arguments The Evolution Revolution • Fossils in sedimentary rock also laid groundwork for Darwin • Layers of rock, sand and mud settle over time and form layers or “strata” • French paleontologist George Cuvier noticed that different species appear while others disappear from strata to strata. – He was against the idea of gradual evolutionary change – Catastrophism – each boundry between strata represents a catastrophe that destroyed many species at that time. The Evolution Revolution • Gradualism – profound change can take place through the cumulative effect of slow but continuous processes – Valleys were formed by rivers wearing through rocks and marine fossils were formed from particles that had eroded from the land and b The Evolution Revolution • Uniformitarianism – the same geologic processes are operating today as in the past, and at the same rate – Proposed by the leading geologist of Darwin’s time, Charles Lyell The Evolution Revolution • Lamarck – French biologist who recognized that evolutionary change explains the fossil record and organisms’ adaptations to their environments – Remembered more for the fact that he described the incorrect mechanism for this. – Published theory in 1809 (year Darwin was born) • Use and disuse (giraffe stretching neck) • Inheritance of acquired characteristics (giraffe again) Darwin and TOS • Father wanted him to go to med school but he hated it, so he enrolled in Cambridge University to become a clergyman – Many interested in science did this: think Mendel • Rode on the HMS Beagle around the world with Captain Robert FitzRoy in 1831 (age of 22) Darwin’s Observations • Many plants in South America had adapted to their environments • Plants in temperate regions of South America were more similar to plants in tropic regions of South American than they were to plants of temperate regions in Europe • Fossils he found were different, but distinctly “South American” in comparison to present species Galapagos • Most impacted by stop at the Galapagos Islands in the south Pacific – Very unusual species he found there – Most fascinated by finches – a common bird elsewhere but somehow different in Galapagos • Realized that finches’ adaptations were from having to adapt to the food sources on this very different island Publication Process • Darwin returned to London, staying at home from illness most of the time, and not publishing his theories on natural selection and adaptation for fear of the uproar it would cause • He was encouraged by Lyell to publish before someone else. • June 1858, Alfred Russel Wallace sent a transcript for Darwin to evaluate, and Darwin quickly sent his TOS manuscript to publishers Summary of TOS • Biological diversity is the product of evolution • Descent with Modification – unity in life, with all organisms related through descent from an ancestor that lived in the remote past. As descendants from that ancestor moved to different environments, they had to adapt – Most branches in evolution are dead ends – 99% of all species that have ever lived are extinct, so no gap or link species exist • Natural selection. Darwin formed his hypothesis of natural selection by drawing two inferences based on his observations. • Observation #1 : Individuals of a population exhibit variation in their traits. • Observation #2 : Many traits are heritable. • Observation #3 : Many species overproduce offspring. • Observation #4 : Resources are limited; many of these offspring do not survive due to competition for those resources. • Inference #1 (natural selection): Individuals whose traits give them a high probability of surviving and reproducing are likely to leave more offspring than others. • Inference #2 (adaptation): A population will accumulate favorable traits over generations and become adapted to its environment. Summary of TOS • Artificial Selection – humans have modified other species over many generations by selecting and breeding individuals that possess desired traits Emphasized Points • Natural selection may occur between individuals, but individuals do not evolve, populations evolve • Natural selection can amplify or diminish ONLY heritable traits Applying Darwin’s Theory • Natural Selection – Differential Predation and Guppy Populations • Due to predation, larger and faster fish were more dominant in an area, when there was a predator – Evolution of Drug-Resistant HIV • Different varieties of HIV exist, and some are resistant to begin with. After just a few weeks, the resistant strains comprise 100% of the virus population, due to selection. Applying Darwin’ Theory • Homology, Biogeography, the Fossil Record – Homology – similarity resulting from common ancestry – Anatomical Homology • Homologous Structures – variations on a structural theme that is present in common ancestors – Comparative Embryology – comparison of early stages of animal development – Vestigial Organs – structures of marginal, if any, importance to the organism – once were important to ancestors – Molecular Homology • All forms of life use DNA and RNA Applying Darwin’s Theory – Biogeography – geographic distributions of species • Closely related species tend to be found in the same geographic regions, whereas some ecological niches in distant regions are occupied by very different (though sometimes similar-looking) species • Endemic – species found only in one place in the world and nowhere else – Fossil Record • Prokayotes should be the oldest in the fossil record, and they seem to be