Chapter 22 Descent with Modification: A Darwinian View of Life

evolution** – processes that have transformed life on Earth from its earliest beginnings to its current diversity **greatest underlying principle in biology 1859 Darwin published On the Origin of Species by Means of Natural Selection arguing that species evolved from ancestral forms by natural selection -revolutionized scientific thought, but contrasted sharply with views of the time

Figure Charles Darwin in 1859, the year The Origin of Species was published

Figure 22.0 Title page from The Origin of Species

Figure Camouflage as an example of evolutionary adaptation

Linnaeus – (early 1800’s) “father of taxonomy” – branch of biology concerned with naming and classifying diverse forms of life -developed binomial nomenclature – 2 part naming system

Cuvier – a paleontologist; proponent of catastrophism – Earth’s changes are due to catastrophic events; used fossils to back up his claim Hutton & Lyell – geologists; supported idea of catastrophic events, but changing of Earth gradually Lamarck – believed acquired characteristics could be passed onto organisms (ex: giraffe neck length)

Darwin’s voyage – 1831 (HMS Beagle) -took him to Galapagos Islands where he developed the idea of adaptation to environment Wallace – 1858 – developed idea of natural selection independently from Darwin & published manuscript (before Darwin, but his was not as thorough)

Figure 22.5 The Voyage of HMS Beagle

Darwin’s ideas – descent with modification - unknown ancestral prototype (no idea of genetics) - variation of individuals made differential reproductive success - those best adapted (most fit) leave the most offspring (passing on their characteristics)

Figure 22.9 A few of the color variations in a population of Asian lady beetles

Malthus – many organisms reproduce, few offspring survive 1930’s – Population genetics – emphasizes extensive genetic variations within populations & recognizes importance of quantitative inheritance (reconciliation of Mendelism & Darwinism) 1940’s – neoDarwinism – (modern synthesis) – importance of populations, gradualism, & modern genetics

Natural selection -the idea that organisms with favorable traits are more likely to survive and reproduce

Evidence for evolution: 1)Biogeography – geographical distribution of a species ex: endemic island species (Australia, Galapagos, Madagascar) 2)Fossil record – supports common descent ex: Archeopteryx links birds, reptiles 3)Taxonomy – reflected branching genealogy

Figure 22.4 Strata of sedimentary rock at the Grand Canyon

4) Comparative anatomy – anatomical similarities ex: homologous structures, vestigial organs 5)Comparative embryology – helps identify anatomical homology less apparent in adults; reflects genetic similarity ex: comparing embryos of different vertebrates 6) Molecular biology – similarities in DNA sequences & protein sequences; supports common descent

Figure Homologous structures: anatomical signs of descent with modification

Table 22.1 Molecular Data and the Evolutionary Relationships of Vertebrates

Chapter 23 The Evolution of Populations

Population -a localized group of individuals belonging to the same species Species -a group of populations whose individuals have the potential to interbreed and produce fertile offspring in nature

Gene pool – the total aggregate of genes in a population at any one time Hardy-Weinberg theorem - frequencies of alleles and genotypes in a population remain constant over time

Hardy-Weinberg theorem For a population to be in Hardy-Weinberg equilibrium, these 5 conditions must be met: 1) large population size 2) no migration or emigration 3) no net mutations 4) random mating 5) no natural selection

Hardy-Weinberg equation p 2 + 2pq +q 2 = 1

Example 500 plants 480 red (320 RR, 160 Rr) 20 white (rr) diploid = 1000 alleles R = 800 (320 x 2 = 640 RR, 160 x 1 = 160 Rr) = 800/1000 =.8 = 80% r =.2 = 20% R = p, r = q (.8) 2 + 2(.8)(.2) + (.2) 2 = = 1

Figure 23.4 Genetic drift

Figure 23.3b The Hardy-Weinberg theorem

Figure 23.3a The Hardy-Weinberg theorem

Microevolution -relative frequencies of alleles in a population change over a succession of generations within a gene pool

Causes of Microevolution 1)Genetic drift – changes due to chance usu. in small populations -conditions which may reduce population size: a) bottleneck effect – population drastically reduced by disaster, killing unselectively ex: cheetah population – reduced in the ice age, then trophy hunted to near extinction b) founder effect – genetic drift in a new colony for that species ex: colonizing isolated island, lake, etc.

Figure 23.5 The bottleneck effect: an analogy

Figure 23.5x Cheetahs, the bottleneck effect

2)Gene flow – migration of fertile individuals between populations 3)Mutation – changes in DNA 4)Nonrandom mating - may include: selective breeding – choosing mates that are close by (may lead to inbreeding; extreme is self-fertilization) or assortative mating – individuals select partners like themselves in phenotype

Figure 23.16x1 Sexual selection and the evolution of male appearance

5)Natural selection – (variation is at the core) polymorphism – when 2 or more distinct forms are present in a population ex: M & F lions (sexual dimorphism); may be balanced (remains set in population)

Figure 23.16x2 Male peacock

Figure 23x2 Polymorphism

geographical variation – genetic differences in population of a species varies regionally ex: cline – graded change along geographic axis recombination & mutation add variety

Figure 23.8 Clinal variation in a plant

Variation may be preserved through: diploidy – hides recessive alleles balanced polymorphism – heterozygote advantage ex: sickle cell anemia Aa – resistant to malaria AA – susceptible to malaria aa – sickle cell anemia

Figure Diversifying selection in a finch population

Figure 23.12x Normal and sickled cells

Figure Mapping malaria and the sickle-cell allele

Fitness – relative contribution an individual makes to the gene pool of the next generation Relative fitness – contribution of a genotype to the next generation compared to the contributions of alternative genotypes for the same locus

Modes of Natural Selection 1)Stabilizing selection – favors the mean 2)Directional selection – favors one extreme phenotype over another 3)Diversifying selection – favors both ends of the spectrum, & not the mean **natural selection acts on individuals, but populations evolve

Figure Modes of selection