Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 22 Descent with Modification: A Darwinian View of Life Darwin made two major points in his book: Many current species are descendants of ancestral species Natural selection is a mechanism for this evolutionary process Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions The study of fossils helped to lay the groundwork for Darwin’s ideas Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata Video: Grand Canyon Theories of Gradualism Gradualism is the idea that profound change can take place through the cumulative effect of slow but continuous processes Lamarck’s Theory of Evolution Lamarck hypothesized that species evolve through use and disuse and the inheritance of acquired traits The mechanisms he proposed are unsupported by evidence Rats and giraffs LE 22-6 Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp. Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground. Insect eater. The green warbler finch (Certhidea olivacea) used its narrow, pointed beak to grasp insects. The Origin of Species Darwin developed two main ideas: Evolution explains life’s unity and diversity Natural selection is a cause of adaptive evolution The phrase descent with modification summarized Darwin’s perception of the unity of life The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past In the Darwinian view, the history of life is like a tree with branches representing life’s diversity LE 22-7 Sirenia Hyracoidea (Manatees (Hyraxes) and relatives) 0 10,000 2 5.5 24 34 Elephas Loxodonta Loxodonta cyclotis maximus africana (Africa) (Africa) (Asia) Natural Selection and Adaptation Evolutionary biologist Ernst Mayr has dissected the logic of Darwin’s theory into three inferences based on five observations Observation #1: For any species, population sizes would increase exponentially if all individuals that are born reproduced successfully Observation #2: Populations tend to be stable in size, except for seasonal fluctuations Observation #3: Resources are limited Inference #1: Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving Observation #4: Members of a population vary extensively in their characteristics; no two individuals are exactly alike Observation #5: Much of this variation is heritable Inference #2: Survival depends in part on inherited traits; individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals Inference #3: This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over generations Artificial Selection In artificial selection, humans have modified other species over many generations by selecting and breeding individuals with desired traits LE 22-10 Terminal bud Lateral buds Brussels sprouts Cabbage Leaves Flower clusters Kale Cauliflower Stem Flowers and stems Broccoli Wild mustard Kohlrabi Summary of Natural Selection Natural selection is differential success in reproduction from interaction between individuals that vary in heritable traits and their environment Natural selection produces an increase over time in adaptation of organisms to their environment If an environment changes over time, natural selection may result in adaptation to these new conditions Video: Seahorse Camouflage LE 22-11 A flower mantid in Malaysia A stick mantid in Africa Darwin’s theory explains a wide range of observations Darwin’s theory of evolution continues to be tested by how effectively it can account for additional observations and experimental outcomes Natural Selection in Action Two examples provide evidence for natural selection: the effect of differential predation on guppy populations and the evolution of drugresistant HIV Researchers have observed natural selection leading to adaptive evolution in guppy populations- Differential Predation in Guppy Populations LE 22-12a Pools with killifish but no guppies prior to transplant Predator: Killifish; preys mainly on small guppies Experimental transplant of guppies Guppies: Larger at sexual maturity than those in “pike-cichlid pools” Predator: Pike-cichlid; preys mainly on large guppies Guppies: Smaller at sexual maturity than those in “killifish pools” 200 160 120 80 40 185.6 161.5 67.5 76.1 Males Females Age of guppies at maturity (days) Mass of guppies at maturity (mg) LE 22-12b 100 80 60 40 20 85.792.3 58.2 48.5 Males Females Control population: Guppies from pools with pike-cichlids as predators Experimental population: Guppies transplanted to pools with killifish as predators The Evolution of DrugResistant HIV The use of drugs to combat HIV selects for viruses resistant to these drugs The ability of bacteria and viruses to evolve rapidly poses a challenge to our society LE 22-13 Percent of HIV resistant to 3TC 100 Patient No. 1 Patient No. 2 75 50 Patient No. 3 25 0 0 2 4 6 Weeks 8 10 12 Homology, Biogeography, and the Fossil Record Evolutionary theory provides a cohesive explanation for many kinds of observations Homology is similarity resulting from common ancestry-Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor LE 22-14 Human Cat Whale Bat Comparative embryology reveals anatomical homologies not visible in adult organisms Vestigial organs are remnants of structures that served important functions in the organism’s ancestors Molecular Homologies Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor Homologies and the Tree of Life The Darwinian concept of an evolutionary tree of life can explain homologies Anatomical resemblances among species are generally reflected in their molecules, genes, and gene products LE 22-16 Species Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide Human 100% Rhesus monkey 95% 87% Mouse 69% Chicken 54% Frog Lamprey 14% Biogeography Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution Some similar mammals that have adapted to similar environments have evolved independently from different ancestors LE 22-17 NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel The Fossil Record The succession of forms observed in the fossil record is consistent with other inferences about the major branches of descent in the tree of life The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record Paleontologists have discovered fossils of many such transitional forms