Chapter 22 Notes on Theory of Natural Selection PDF

Theory of Natural Selection Chapter 22 This is the seminal theory in evolutionary biology. Descent with Modification:...

Theory of Natural Selection Chapter 22 This is the seminal theory in evolutionary biology. Descent with Modification: The phrases “survival of the fittest” and A Darwinian View of Life “descent with modification” epitomize the theory. The Theory of Natural Selection appeared in On the Origin of Species... made a tremendous the book On the Origin of Species by Means of impact in the Western world because the Natural Selection published in 1859 by Theory of Natural Selection challenged literal Charles Darwin. views of Biblical creation. Darwin is credited as the first scientist to It also challenged ideas on the nature of explain evolution by presenting a mechanism, organisms that were prevalent among and by providing a large body of evidence to scientists of the Victorian age. back up his theory. Context Darwin and Wallace Up until 1859, scientists worked in a non- evolutionary settings. The concept of the “great Although Charles Darwin is credited with the chain of being” was predominant narrative for Theory of Natural Selection, another British life. The “great chain of being” is the idea that life can naturalist, Alfred Russel Wallace, realized be categorized by stages of complexity. It stems independently that evolution was driven by from Christian theological dialogues of the early natural selection. Medieval period. https://www.researchgate.net/publication/ 51453528_From_the_scala_naturae_to_the_symbiogenetic_and_dynamic_tree_of_life  Wallace studied biogeography in Asia and in 1858 sent an essay Acknowledging that Darwin had worked on summarizing his ideas to his theory much longer than had Wallace, and Darwin. had amassed much more evidence, Wallace conceded that Darwin should be credited Their mutual friend with the idea of natural selection. Charles Lyell organized joint scientific talks in London in 1858. Alfred Russel Wallace Impact Each individual of a given species was thought to be interchangeable with any Darwin’s book shocked and outraged many of other individual. his colleagues as well as clergy. Differences among individuals were At the time it was commonly believed that regarded as “imperfections” from the species, as rungs in the great chain of being, archetype of the species (i.e. those were divinely ordained and immutable individuals made by a creator deity). (unchangeable). Evolution was thought to be a real The predominant idea was that members of a phenomenon by some early scientists, but species were merely variants on a divine they did not have an explanatory theme. mechanism. Thus individual members of a species differed In 1809, Jean-Baptiste de Monet, Chevalier from the archetype much as cookies that were de Lamarck published his idea of cut from the same cooker cutter might vary inheritance of acquired characteristics as from each other. the explanatory mechanism. https://www.allrecipes.com/recipe/230238/gingerbread-men-cookies/ https://en.wikipedia.org/wiki/Jean-Baptiste_Lamarck Lamarck worked at a time (late 1700s, early These fossils included species of mammals 1800s) when extinction was not regarded to be a that clearly did not exist in modern faunas. real phenomenon. Lamarck concluded that, because species do He is credited as the first scientist to propose that not go extinct (according to the reasoning of species were not immutable. This came as a the time), that they must have changed into result of his research of the mammalian fossils of another species, i.e. the fossil species he Europe. studied must be the ancestors of modern species. But what was the agent or mechanism of A classic example is the Larmarckian evolutionary change? explanation for the long neck of giraffes. Lamarck proposed that organisms had an According to Lamarck’s idea, giraffes have intrinsic force that directed evolution in a long necks because they are descended from species. Thus, Lamarckian evolution has a a series of ancestors that stretched their goal. A corollary of this idea is that the necks in order to reach leaves of tall trees. external environment has little or no effect on the evolution of a species. https://en.wikipedia.org/wiki/Jean-Baptiste_Lamarck By virtue of its intrinsic force, each ancestral Darwin and the Beagle giraffe acquired a small but definite increase in neck length, which it passed on to its Darwin was admitted to university as a pre- offspring. medical student. Lamarck’s explanation was not widely Two years later he switched his studies to the accepted because there was no evidence to arts (theology), which involved natural history support the idea that acquired characteristics studies. were inheritable.  In 1831, soon after graduating, his former botany professor put forward Darwin’s name for the position of ship’s naturalist on H.M.S. Beagle. This was a self-funded position, for a two year geographical (charting) survey of the coast of South America. Figure 22.2 The intellectual context of Darwin’s life and ideas The voyage of Beagle lasted five years and circumnavigated the globe. Darwin visited and made collections from a variety of regions in South America and elsewhere. He collected plant and animals, as well as minerals and fossils, from South American localities and the Galapagos Islands, and had them shipped back to England. Figure 22.2 The voyage of the H.M.S. Beagle When the Beagle visited the Galápagos In addition to visiting the Amazon rain forest, Islands, Darwin made collections of the plant Darwin also made collections in Patagonia, and animal life there, including its now famous including fossils of extinct mammals. avifauna (esp. finches). Following an earthquake in Chile, Darwin At the time, Darwin believed that the finches examined the local geology and concluded were not closely related, but a colleague back that western South America was rising out of in England concluded that the Galápagos the Pacific Ocean. finches were descended from a single ancestral species.  The Beagle sailed across the Pacific to Australia, and from there to southern Africa, and back to South America before heading home to England. These visits gave Darwin opportunities to examine similar ecosystems and communities across three continents. Figure 22.6 Three examples of beak variation in Galápagos finchs Lyell’s work was the (then) state of the art book on the science of geology. Geology had Darwin was able to bring a small library begun in the mid-1700s with James Hutton’s on the voyage. initial observations and investigations into the formation of rocks. One of these was the geology text Principles of Geology published by Hutton, a.k.a. the “Father of Modern Charles Lyell in 1830. Geology”, first studied sedimentary rocks. He devised the principle of superposition. https://anthropology.iresearchnet.com/charles-lyell/#google_vignette https://www.geologyin.com/2023/02/the-principle-of-superposition.html James Hutton also devised the principle of Context uniformitarianism, which states that forces James Ussher was the Church of Ireland which operated in the past are working today Archbishop of Armagh and Primate of All and can be observed. Ireland between 1625 and 1656. Hutton came to the conclusion that Using clues from the Bible, he calculated the sedimentary processes were gradual and very age of the Universe and determined that the slow and that the Earth must be millions of first day of biblical creation was October 23, years old. 4004 BC. Charles Lyell’s work, and that of other naturalists, such as Georges Cuvier, expanded on Hutton’s pioneering studies by mapping out the distributions of fossils across Europe. Georges Cuvier documented that older rocks often preserved relatives of those in younger rocks, but those from older strata (rock layers) were less complex. Figure 22.3 Formation of sedimentary strata with fossils The lasting impression that Darwin received Another strong influence on Darwin’s from Lyell’s work was the idea that geological thinking was a 1798 economic tract by processes occur over extremely long time Thomas Malthus entitled Essay on the spans. Principle of Population. Darwin realized that if geological processes Malthus recognized that people had the transpired over enormous spans of time, potential to reproduce exponentially, perhaps other natural phenomena did so, as whereas resources (e.g. crops) could be well. increased only arithmetically. https://www.proprofs.com/quiz-school/quizzes/malthusian-theory-of-population-change-quiz Malthus argued that if human population Finally, Darwin read an 1809 pamphlet by John growth could not be regulated, it would Sebright called The Art of Improving Breeds of outstrip available food supplies, leading to Domestic Animals. famine and the breakdown of social order. Sebright’s statement “The weak do not Darwin concluded that Malthus’s observations survive long enough to pass on their traits” and argument could be extended to natural made a great impression on Darwin, who was populations of plants and animals. trying to make sense of the phenomenon of variation in species.  Impact: the variation exhibited by the Darwin synthesized the ideas generated from individuals of plant and animals species his readings of Lyell, Malthus, and Sebright. could be divided into “desirable” and Noting that many plants and animals are “unwanted” traits by breeders. capable of producing great numbers of offspring, Darwin realized that Malthus’s Some of this variation must be inheritable if argument for unregulated population growth breeders can concentrate preferred features could be applied to populations of natural in a given breed of domestic animal, plant, (wild) species. etc. https://www.nationalgeographic.com/animals/article/these-mom-fish-cannibalize-their-babies https://www.crownandchamparesorts.com/magazine/press-sea-turtle-hatching-at-kagi-maldives/ https://www.dairydiscoveryzone.com/blog/name-cow-6-great-dairy-breeds https://www.wildthingsfood.co.uk/news/the-secret-lives-of-ducklings/ Darwin was aware, however, that wild populations of organisms do not change greatly from year to year. Accordingly, only a fraction of offspring produced every year became adults that go on to have offspring of their own. The rest must perish. https://www.the-mad-scientist.net/evolution.html Figure 22.10 Overproduction of offspring Why do most individuals of a species fail to Taking Sebright’s observations into account, make it to adulthood? Darwin concluded that most offspring in a given generation die before reaching Plant and animal species rely on resources reproductive age. that are particular to them, and such resources are invariably limited. This explains Those individuals die mainly because they do why wild populations do not vary greatly from not have the traits to compete successfully for year to year. the limited resources. Darwin also developed his ideas from other lines of evidence, including interviews with farmers and breeders. Darwin was able to appreciate that wild populations could yield numerous plant varieties and animal breeds, depending on characteristics sought by breeders. https://link.springer.com/chapter/10.1007/978-94-017-7749-0_5 Figure 22.9 Articifial selection of a species of wild mustard Darwin proposed that the variation exhibited The process of concentrating desired traits in by the individuals of a species was key to the domesticated organisms is called artificial differential survival of the offspring. selection. He proposed that some traits were superior to In On the Origin of Species... Darwin often others, and that individuals with these drew upon examples of artificial selection as superior traits had an advantage over those analogies in his argument for natural selection. that lacked them. The individuals with superior traits were better able to compete for resources. Thus, competition was an important component of natural selection. The superior traits had to be heritable, so that successful individuals could pass the trait on to their offspring. Figure 22.10 Variation in a population  Darwin argued that the advantage of the As with geological processes, Darwin superior trait could be very slight, but over believed that natural selection operated time, individuals with such traits would over long time spans. Thus, it is a slow, proliferate in the population. gradual (or graduated) process. By this process, populations and eventually Because there was no need to invoke a species change permanently, and evolution creator deity to account for this process, occurs. Darwin dubbed his theory natural selection. https://www.researchgate.net/publication/ 334169227_learnPopGen_An_R_package_for_population_genetic_simulation_and_numerical_analysis Darwin envisioned descent with modification Interestingly, Darwin did not use the word occurring over a very long period of time, evolution (he did use the word evolved in the acting on a single ancestor to produce the last sentence). biodiversity we see today. Instead, he used the term descent with In his 1837 sketch, he anticipated the modification, which evoked both (1) the evolutionary trees we use today. The ancestor concept of common ancestry that united is “1”, the letters are living groups organisms, organisms together, and (2) the modificaton and the unlabelled branches are extinct taxa. of lineages that results from natural selection. Darwin thought that the branching pattern and extinction could explain the Figure 22.7 “I morphological gaps we see between groups. think...” In this 1837 sketch, Darwin envisioned the The evolutionary tree in Figure 22.8 shows branching pattern of evolution the relationships among 5 living lineages and 7 extinct lineages. The extinct lineages create a morphological gap between living elephants and manatees and hyraxes.  Natural selection as a process It is important to recognize that natural Figure 22.8 selection is a non-directed, aimless process Descent with (i.e. there is no “goal”). modification It is often described as a blind and automated process. It is often described as “blind”, “aimless”, and “non-directed” because selective Describing natural selection as a blind and forces operate in specific contexts. non-directed process makes it a difficult A feature or trait that might be concept for skeptics to comprehend. unfavourable in one situation may be neutral or desirable in another, different This is mainly because modern organisms selective regime. An example is blue eyes. appear to be so well adapted to their https://knowyourmeme.com/photos/2013433-rfreefolk respective environments. https://kwekudee-tripdownmemorylane.blogspot.com/2013/02/blacks-with-blue-eyes-natural.html httpsov/https://www.coolgeography.co.uk/A-level/AQA/Year%2013/Weather%20and%20climate/ Climate%20controls/Insolation%20and%20the%20atmosphere.htm/fossils/dinosaurs.htm Nature’s failures are not around to remind us Modern organisms appear to be well adapted of the power of natural selection. because we see only the descendants of those organisms that were successful in passing their We need only look at the fossil record to see genes to the next generation. species that were successful in their own time, but for one reason or another failed to make it In other words, we see the descendants of the to the present. “winners”, not the “losers”. https://www.nps.gov/subjects/fossils/dinosaurs.htm https://evolutionnews.org/2023/11/were-neanderthals-and-humans-the-same-species/