BIO1022 Week 1: Evolving Life: Natural Selection and the Tree of Life Note: This document outlines the major concepts for the week and is intended as a basis for structuring your study. The question... s listed following this page are only intended to guide your understanding of the week’s content and not as example/practice questions. Answers will not be provided. Week 1 Learning Outcomes: 1. Explain the main requirements for natural selection to occur, and compare with artificial and sexual selection. • Explain the conclusion that Darwin and Wallace came to that helps explain the evolution of species, and describe how it relies on the observations of Malthus. Malthus observed in his book that population will increase, theoretically, geometrically or exponentially. However, this is not the case in nature, because resources which the individuals depending on are scarce. Individuals in a population will compete to gain access to food, space, mating partner, etc. Many individuals would not reproduce and produce offsprings because of this competition. Individuals that are most adapted to their environments will be able to live longer and compete more strongly. This adaptation is caused by an advantageous variation (allele) in their genetic material. This, in turn, would lead to their success in leaving more offsprings. The offsprings would carry their genetic material (which have had the advantageous trait), which will help themselves to produce more offsprings. Eventually, the proportion of this advantageous allele in the population would increase, and over time, this allele will be fixed in the population, that is, every individual would carry this allele. • Compare the patterns of natural selection with artificial and sexual selection Natural selection works to increase the frequency of an advantageous allele (positive selection) and decrease the frequency of a deleterious (that is, disadvantageous or harmful) allele in a population. Natural selection can be - stabilising, favouring the status quo (middle-class traits) and acts again extremes. For example, if a baby is too small, it may causes the baby to die; however, a baby too large would result in a higher probability of complication that results in the death of itself and it’s mother. Selection would favour babies born with “normal” or “ordinary” weight. - directional, leading to a change over time. For example, consider a population of small-beaked finch which feeds on small seeds. A drought killed most of the plants producing small seeds, leaving only vegetations producing large seeds. Natural selection favours finches with larger beaks that can handle larger seeds. Eventually, the finch population evolved bigger beak size.- disruptive, favouring the extremes and opposing the intermediate forms. 2. Describe the biological species concepts, its limitations and alternative species concepts. BSC states that species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups. Their limitations include: - it is impossible to apply this concept in a field expedition to determine whether two individuals come from a same species or not; this may be overcome by the morphospecies concept: members of the same species usually, but not always, look alike. - it is inapplicable to asexual organisms e.g. bacteria, since they do not exchange genetic materials (although some species may transfer genetic materials with each other, a process called conjugation) - it is inapplicable to extinct organisms, since... well, they could not reproduce. - the presence of ring species, species with two populations reproductively, but not genetically isolated. Two populations, A and B, may not be able to interbreed with each other, but population A can do so with other population, C. Population C, in turn, is able to interbreed with population B, enabling gene flow between population A and B. [Show More]
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