90 likes | 214 Vues
CHAPTER 10. Stacie Daer. Are all features of living organisms adaptations? How could you determine if a trait in an organism is a product of evolution by natural selection?.
E N D
CHAPTER 10 Stacie Daer
Are all features of living organisms adaptations? How could you determine if a trait in an organism is a product of evolution by natural selection?
An adaptation is a trait that is favored by natural selection and increases an individual’s fitness in a particular environment. • Fitness is the relative survival and reproduction of one variant compared to others in the same population. • Natural Selection is the process by which individuals with certain traits have greater survival and reproduction than individuals who lack these traits, resulting in an increase in the frequency of successful alleles and a decrease in the frequency of unsuccessful ones. Belk and Borden
“Adaptations can take many forms: a behavior that allows better evasion of predators, a protein that functions better at body temperature, or an anatomical feature that allows the organism to access a valuable new resource — all of these might be adaptations. Many of the things that impress us most in nature are thought to be adaptations.” http://evolution.berkeley.edu/evolibrary
Not all features are adaptations! • Biologists find it difficult to be certain whether any particular structure of an organism arose by selection and hence can be called adaptive or whether it arose by chance and is selectively neutral. ( Hair color) • Sometimes there is no obvious reason for the presence of a certain trait. This can be because the utility of a trait is lost and does not appear adaptive now, the function of a trait is unknown, or the trait is a result of another trait that is adaptive. www.encarta.msn.com, www.blackwellpublishing.com
Linked Genes • Genes are located on the same chromosome. • One gene is passed on as a result of natural selection, and the linked gene is also passed on even though it isn’t an adaptation. • Example) red hair and light skin Belk and Borden,www.anthro.palomar.edu
Vestigial Structures • Vestigial structures are features that were adaptations for an organism’s ancestor, but now have evolved to serve no function because the environment changed. www.images.livescience.com,http://evolution.berkeley.edu
While not all evolutionary changes are a result of adaptation, all adaptations can be explained by natural selection. www.blackwellpublishing.com,http://evolution.berkeley.edu
Other Mechanisms of Evolution • Genetic Drift (luck) • Change in allele frequency that occurs as a result of chance. • Gene Flow (migration) • Spread of an allele throughout a species gene pool. Belk and Borden, www.evolutionl.berkeley.edu