BIOLOGY 1202- Descent with Modification: a Darwinian View of Life- What is evolution and adaptation?o Evolution: two main ideas 1. Change over time of the genetic composition of a population 2. Decent of modern organisms with modification from preexisting organismso Evolutionary adaptation Accumulation of inherited characteristics that enhance organisms’ ability to survive in specific environments- Pre-Darwinian Theory of Evolutiono Catastrophism The principle that events in the past occurred suddenly by mechanisms not operating todayo Uniformitarianism Geologic change results from mechanisms that operated in the past in the same manner as at the present timeo Gradualism The hypothesis that evolution proceeds chiefly by the accumulation of gradual changeso Lamarck Use and disuse- Bodies of living organisms are modified through the use or disuse of parts Inheritance of acquired characteristics- These modifications are inherited by offspringo These ideas turned out to be wrong- Evolution by Natural Selectiono Darwin and Wallace developed the theory independently Darwin – voyage of the Beagle Wallace – naturalist in Indonesia- Natural Selectiono The unequal survival and reproduction of organisms due to environmental forces, resulting in the preservation of favorable adaptationso Process “selects” from what is available in the gene poolo New characteristics are not created on demand Unfavorable traits decrease in frequency, favorable traits increase- Mechanisms Behind Natural Selectiono Observations Individuals in a population vary in their heritable characteristics Organisms produce more offspring than the environment can supporto Inferences Individuals that are well suited to their environment tend to leave more offspring than other individuals Over time, favorable traits accumulate in the population- Natural Selection: A Summaryo Natural selection is a process in which individuals that have certain heritable traits survive and reproduce at a higher rate than other individuals because of those traits.o Over time, natural selection can increase the match between organisms and their environment.o If an environment changes, or if individuals move to a new environment, natural selection may result in adaptation to these new conditions, sometimes giving rise to new species.o Although natural selection occurs through interactions between individual organisms and their environment, individuals do not evolve. It is the population that evolves over time.o Natural selection can amplify or diminish only those heritable traits that differ among the individuals in a population. Thus, even if a trait is heritable, if all the individuals in a population are genetically identical for that trait, evolution by natural selection cannot occur.o Environmental factors vary from place to place and over time. A trait that is favorable in one place or time may be useless – or even detrimental – in other places or times. Natural selection is always operating, but which traits are favored depends on the context in which a species lives and mates.- Artificial Selectiono Selective breeding of organisms to encourage the occurrence of desirable traitso Analogous to natural selection- Evolution is supported by an overwhelming amount of scientific evidence- Homologous and Analogous Structureso Homologous Structures or other attributes in different species that resemble each other because of common ancestry Not similar in function, similar in structure- Example: mammalian forelimbso Analogous Structures that are similar in function but not in structure and developmental and evolutionary origin- Homologous Structures: Vertebrate Embryoso All vertebrates share similar developmental geneso Differences arise by some genes being switched on or off at varying times during development- Homologous Structures: Biochemistry and Molecular Biologyo DNA is universal genetic materialo All life forms use approximately the same 20 amino acids to make proteinso All use ATP as the primary form of cellular energyo All use RNA and ribosomes to make proteins- Trees vs. Scala Naturaeo Scala Naturae Ladder of nature (see pg 453)o Evolution not about climbing “ladder of nature” from lower to highero Evolution is a “bush” with lineages branching from one another- Convergent Evolutiono Similarity between 2 organisms, structures, or molecules due to independent evolution along similar lines rather than descent from a common ancestor- Fossil Recordo Show change in organisms through timeo Change in types of organisms Past organisms differ from present-day organisms Many species have become extincto Not only provides evidence of small-scale changes but of origin of major groups E.g., the cetaceans- The Evolution of Populationso The smallest unit of evolution One common misconception about evolution is that individual organisms evolveduring their lifetime Evolutionary processes (e.g., natural selection) act on individuals, but populations evolve- Genetic variation makes evolution possible- Mutationo Mutations: changes in nucleotide sequence of DNA Source of new alleles and geneso Point mutation: change in one nucleotide base in a geneo Chromosomal mutations: delete, disrupt, or rearrange many loci on a chromosomeo Gene duplications: duplication of whole segments of a chromosomeo Mutation rate averages 1 in every 100,000 genes per generation- Sexual Recombinationo In sexually reproducing organisms, sexual recombination produces most of the variability in each generation Crossing over during prophase I Independent assortment during metaphase I- Variation within a populationo Discrete characters: classified on an either-or basis E.g., flower color in pea plantso Quantitative characters: vary along a continuum within a population E.g., height, weight- The Hardy-Weinberg equation can be used to test whether a population is evolving- Populationso A group of individuals of the same species living in a certain defined area- Hardy-Weinberg Equilibriumo Describes a population that is not evolving (i.e., allele frequencies don’t change)o Five assumptions behind H-W equilibrium 1. No mutations 2. Large population size 3. No gene flow- No migration among populations 4. No natural selection 5. Random mating- Equal chance of mating with any other in population- Allele & Genotype Frequencieso Allele frequencies p =
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