GEOLOGY 12 CHAPTER 8 PATTERNS OF EVOLUTION NOTES EVIDENCE FOR EVOLUTION INDIRECT fossils (many forms now extinct) changes in a single species of snail DIRECT common ancestry (adaptive radiation) similar (homologous) structures vestigial organs (suggests common ancestry) biochemistry (molecular unity; see Unit 2) embryology (study of embryo development) genetics (cellular unity, DNA materials) GENETICS Trees of Life COMPARATIVE ANATOMY
HOMOLOGOUS VS ANALOGOUS STRUCTURES aka Analogous Structures NOTE: ANALOGOUS STRUCTURES Analogous structures are products of CONVERGENT EVOLUTION. The structures serve the same function, but have different origins. The pectoral fin of a shark and the flipper of a whale are analogous. The wing of an insect and the wing of a bird are also analogous structures. COMPARATIVE ANATOMY page 2
TYPES OF EVOLUTION KEY IDEA The basic evolutionary mechanisms mutation, migration, genetic drift, and natural selection can produce major evolutionary change if given enough time. PUNCTUATED EQUILIBRIUM VS GRADUALISM The "PUNCTUATED EQUILIBRIUM" theory was proposed as a criticism of the traditional Darwinian theory of evolution. ELDREDGE and GOULD observed that evolution tends to happen in FITS AND STARTS, sometimes moving very fast, sometimes moving very slowly or not at all. On the other hand, typical variations tend to be small. Therefore, DARWIN saw evolution as a SLOW, continuous process, without sudden jumps. (GRADUALISM) However, if you study the FOSSILS of organisms found in geological layers, you will see long intervals in which nothing changed ("equilibrium"), "punctuated" by short, revolutionary transitions, in which species became extinct and replaced by wholly new forms. Instead of a slow, continuous progression, the evolution of life on Earth seems more like the life of a soldier or a fire fighter: long periods of boredom interrupted by rare moments of terror. MICROEVOLUTION VS MACROEVOLUTION MICROEVOLUTION is evolution on a small scale within a single population. House sparrows have adapted to the climate of North America, mosquitoes have evolved in response to global warming, and insects have evolved resistance to our pesticides. These are all examples of microevolution evolution on a small scale. Macroevolution is evolution on a grand scale what we see when we look at the overall history of life: stability, change, lineages arising, and extinction. MUTATION CROSSING OVER during meiosis produces variety within a species but MUTATION is the ultimate source of NEW genetic varieties in a species. GENE FLOW can also be responsible for the introduction of NEW ALLELES into a population of a species but, generally, the most rapid and dramatic evolution is due to NATURAL SELECTION. A process like MUTATION might seem too small-scale to influence a pattern as amazing as the number of different beetles, or as large as the difference between dogs and pine trees, BUT IT S NOT. Life on Earth has been accumulating mutations and passing them through the filter of natural selection for 3.8 billion years more than enough time for evolutionary processes to produce its biodiversity history. page 3
KEY IDEA DIVERGENT and CONVERGENT evolution and CO-EVOLUTION are different ways organisms adapt to the environment. These are examples of how the diversity of life on earth is due to the ever-changing interaction between a species and its environment. CONVERGENT EVOLUTION In the frigid waters of the ocean surrounding ANTARCTICA, fish have a special trait which allows them to survive the big chill. As scientists discovered in the 1960s, the fish have adapted by evolving a kind of ANTIFREEZE. It's composed of molecules called GLYCOPROTEINS that circulate in the blood of the fishes, slightly lowering the temperature at which their body fluids would otherwise freeze and kill them. The glycoproteins surround tiny ice crystals and keep them from growing. It's another of those ingenious evolutionary solutions that seem almost too clever to be true. But consider this: Nature did it not once, but at least twice. Fish at the other end of Earth, in the ARCTIC, also have ANTIFREEZE PROTEINS. But those two populations of fish split long before they developed the antifreeze genes and proteins. And, researchers have found, the genes that produce the antifreeze proteins, north and south, are quite different. This is evidence that quite separate, independent episodes of molecular evolution occurred, with the same functional results. This is a dramatic example of CONVERGENT EVOLUTION, when organisms that aren't closely related evolve similar traits as they both adapt to similar environments. CONVERGENT EVOLUTION is also responsible for the WINGS of the bat, the bird, and the pterodactyl. In each case, the forelimbs of these vertebrates morphed over time into wings, but they did so INDEPENDENTLY. the different sorts of ANTEATERS found in Australia, Africa, and America. Though not closely related, they all evolved the "tools" necessary to subsist on an ant diet: a long, sticky tongue, few teeth, a rugged stomach, and large salivary glands. In each case, evolutionary adaptations allow them to exploit a food niche of ants and termites, but the developments occurred INDEPENDENTLY. DIVERGENT EVOLUTION The ADAPTIVE RADIATION of Darwin s finches is one example of DIVERGENT EVOLUTION. Divergent evolution is the process of two or more RELATED SPECIES becoming more and more DISSIMILAR. Some of Darwin s finches page 4
The red fox and the kit fox provide another example of two species that have undergone divergent evolution. The RED FOX lives in mixed farmlands and forests, where its red color helps it blend in with surrounding trees. The KIT FOX lives on the plains and in the deserts, where its sandy color helps conceal it from prey and predators. The ears of the kit fox are larger than those of the red fox. The kit fox's large ears are an adaptation to its desert environment. The enlarged surface area of its ears helps the fox get rid of excess body heat. SIMILARITIES IN STRUCTURE INDICATE that the red fox and the kit fox had a COMMON ANCESTOR. As they adapted to different environments, the APPEARANCE of the two species DIVERGED. CO-EVOLUTION Co-evolution is the joint change of two or more species in close interaction. PREDATORS and their PREY sometimes co-evolve; PARASITES and their HOSTS often co-evolve; plant-eating animals and the plants upon which they feed also co-evolve. One example of co-evolution is between PLANTS and the ANIMALS that pollinate them. In tropical regions BATS visit FLOWERS to eat nectar. The fur on the bat's face and neck picks up pollen, which the bat transfers to the next flower it visits. Bats that feed at flowers have a slender muzzle and a long tongue with a brushed tip. These adaptations aid the bat in feeding. flowers that have coevolved with bats are light in color. Therefore, bats, which are active at night, can easily locate them. The flowers also have a fruity odor attractive to bats. EXTINCTION Over 99% of the species that HAVE EVER lived on Earth have gone EXTINCT! Present day biodiversity is the result of an accumulation of changes due to extinction events over millions of years. EXTINCTION contains three important elements. For geographically WIDESPREAD species, extinction is rare. The largest MASS EXTINCTIONS produce major restructuring of the biosphere wherein some successful groups are eliminated, allowing previously minor groups to expand and diversify. It is generally impossible to predict which species will be VICTIMS of an extinction event. PHYLOGENETIC TREE The Tree of Life represents the PHYLOGENY of organisms (i.e. the history of organism lineages as they change through time). It implies that different species arise from previous forms and that all organisms, from the smallest microbe to the largest plants and vertebrates, are connected. In a phylogenetic tree. Each NODE represents the most recent common ancestor of the descendants, and edge lengths correspond to time estimates. page 5