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Cumulative Selection

Cumulative Selection

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Cumulative Selection

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  1. Cumulative Selection • it has been more difficult to explain the evolution of complex features like an eye or the relationship between flowers and their pollinators • the “blind watchmaker” analogy argues that a complex structure like a watch or an eye could not have arisen by chance and there must be a watchmaker or a Creator • natural selection is not random and, in fact, is the opposite of chance and can easily account for complex structures and relationships

  2. The Evolution of Complex Features • the sudden production of a functioning eye in a worm would require many thousands of beneficial mutations to occur at once in gametes that have no previous genetic code for an eye • the gradual production of an eye would require that each stage in the evolution of a complex eye must have benefited the organism

  3. if a worm ancestor experienced a mutation that resulted in light-sensitive cells may have caused it to stop moving toward light thus avoiding predators or desiccation • such an advantage would be selected until the entire population would exhibit light-sensitive cells • if another mutation produced a pit, a mechanism to detect the direction of light would be produced which would allow the worm to move away from the light which would also be strongly selected for • a deeper pit would increase directionality but decrease sensitivity, which could be improved with a lens

  4. The Evolution of Insect Pollination • flowering plants likely evolved from non-flowering plants that were wind-pollinated, and therefore produced great quantities on non-sticky pollen considering the low probability of sperm encountering egg • sticky pollen would adhere to pollen-foraging insects and perhaps be transferred directly onto the female part of another plant • both organisms would benefit from greater reproductive success of the insect-pollinator and would be followed by other adaptations to attract pollinators such as colourful petals and potent nectar • some adaptations are highly specialialized, such as resembling a queen bee

  5. Altruism • Darwin could not account for altruism, in which the recipient of help is better off than the helper, because it has a genetic basis • many social insects demonstrate altruism, often consisting of non-reproducing sisters raising offspring bred by a queen  because of haplodiploidy (males are haploid and develop from unfertilized eggs, females are diploid and develop from fertilized eggs), females are more closely related to their sisters than to their own offspring • some wasps nest in sister pairs, one laying eggs and the other collecting food  reproductive helpers realize a 30% increase in alleles making it to the next generation than if they had nested alone

  6. Review • Compare and contrast random chance and cumulative selection in evolution. • Can mutations by themselves lead to the development of new inheritable features in a species? Explain. • draw a series of sketches to show how cumulative selection might have resulted in the development of insect-pollinated flowering plants from ancient wind-pollinated ancestors. • Hermaphroditic molluscs try to impregnate each other with their outstreched penis while trying to escape being fertilized themselves. What possible advantage might such molluscs have in avoiding the production of eggs while fertilizing other individuals instead? • What environmental conditions and/or mutations might have led to the evolution of flowers that attract birds or bats, rather than insects, as agents in pollinatiion? • Orb-web spiders have evolved the ability to spin complex netlike webs. Their evolutionary ancestors must have spun less complex webs and gradually gained the ability to spin more complex webs. • Find out what advantages highly sophisticated webs provide to orb-web spiders • Explain how less complex webs would have been advantageous to spider ancestors