The Macroevolutionary Puzzle Chapter 18

Fossils and the Great Deluge Fossils of seashells have been found in rock layers high in the mountains How did they get there? Initial explanation was that they had been deposited during the biblical flood

Evidence of Past Life 1700s Excavations unearthed similar fossil sequences in distant places Scholars began to view these findings as evidence of the connection between Earth history and the history of life

What Do Fossils Tell Us? As a result of mutations, natural selection, and drift, each species is a mosaic of ancestral and novel traits All species that ever evolved are related to one another by way of descent

Macroevolution The large-scale patterns, trends, and rates of change among families and other more inclusive groups of species

Fossils Recognizable evidence of ancient life Fossilized hard parts (most common) Trace fossils (indirect evidence)

Fossilization Organism becomes buried in ash or sediments Rapid burial and a lack of oxygen aid in preservation The organic remains become infused with metal and mineral ions

Stratification Fossils are found in sedimentary rock This type of rock is formed in layers In general, layers closest to the top were formed most recently

Radiometric Dating parent isotope in newly formed rock after one half-lives after two half-lives

Geologic Time Scale Archean eon (oldest interval) Proterozoic eon Paleozoic era Mesozoic era Cenozoic era (most recent) Boundaries based on abrupt transitions in fossil record Correspond to mass extinctions

Record Is Incomplete Fossils have been found for about 250,000 species Most species weren’t preserved Record is biased toward the most accessible regions

Continental Drift Idea that the continents were once joined and have since “drifted” apart Initially based on the shapes Wegener refined the hypothesis and named the theoretical supercontinent Pangea

Changing Land Masses 420 mya 260 mya 65 mya 10 mya

Evidence of Movement Wegener cited evidence from glacial deposits and fossils Later was discovered that magnetic orientations in ancient rocks do not align with the magnetic poles Discovery of seafloor spreading provided a possible mechanism

Plate Tectonics Earth’s crust is fractured into plates Movement of plates is driven by upwelling of molten rock at mid-oceanic ridges As seafloor spreads, older rock is forced down into trenches

Forces of Change crustal margin of one plate being thrust under margin of another plate mid-oceanic range plumes of molten material

Comparative Morphology Comparing body forms and structures of major lineages Guiding principle: When it comes to introducing change in morphology, evolution tends to follow the path of least resistance

Morphological Divergence Change from the body form of a common ancestor Produces homologous structures that may serve different functions

Morphological Divergence 1 2 3 Morphological Divergence PTEROSAUR 4 1 2 CHICKEN 3 STEM REPTILE 2 3 PENGUIN 1 2 3 4 1 5 2 PORPOISE 4 3 5 1 2 BAT 3 4 5 1 2 3 4 HUMAN 5

Morphological Convergence Individuals of different lineages evolve in similar ways under similar environmental pressures Produces analogous structures that serve similar functions

Comparative Development Each animal or plant proceeds through a series of changes in form Similarities in these stages may be clues to evolutionary relationships Mutations that disrupt a key stage of development are selected against

Altering Developmental Programs Some mutations shift a step in a way that natural selection favors Small changes at key steps may bring about major differences Insertion of transposons or gene mutations

Development of Larkspurs Two closely related species have different petal morphology They attract different pollinators side view front view D. decorum flower side view front view D. nudicaule flower

Development of Larkspurs Petal difference arises from a change in the rate of petal development 6 D. decorum 4 Petal length (millimeters) 2 D. nudicaule 10 20 40 Days (after onset of meiosis)

Similar Vertebrate Embryos Alterations that disrupted early development have been selected against FISH REPTILE BIRD MAMMAL

Similar Vertebrate Embryos Aortic arches Adult shark Early human embryo Two-chambered heart Certain veins

Developmental Changes Changes in the onset, rate, or time of completion of development steps can cause allometric changes Adult forms that retain juvenile features

Proportional Changes in Skull Chimpanzee Human

Comparative Biochemistry Kinds and numbers of biochemical traits that species share is a clue to how closely they are related Can compare DNA, RNA, or proteins More similarity means species are more closely related

Comparing Proteins Compare amino acid sequence of proteins produced by the same gene Human cytochrome c (a protein) Identical amino acids in chimpanzee protein Chicken protein differs by 18 amino acids Yeast protein differs by 56

Sequence Conservation Cytochrome c functions in electron transport Deficits in this vital protein would be lethal Long sequences are identical in wheat, yeast, and a primate

Sequence Conservation Yeast Wheat Primate

Nucleic Acid Comparison Use single-stranded DNA or RNA Hybrid molecules are created, then heated The more heat required to break hybrid, the more closely related the species

Molecular Clock Assumption : “Ticks” (neutral mutations) occur at a constant rate Count the number of differences to estimate time of divergence

Taxonomy Field of biology concerned with identifying, naming, and classifying species Somewhat subjective Information about species can be interpreted differently

Binomial System Devised by Carl von Linne Each species has a two-part Latin name First part is generic Second part is specific name

Higher Taxa Kingdom Phylum Class Order Family Inclusive groupings meant to reflect relationships among species

Phylogeny The scientific study of evolutionary relationships among species Practical applications Allows predictions about the needs or weaknesses of one species on the basis of its known relationship to another

A Cladogram shark mammal crocodile bird feathers fur lungs heart

Five-Kingdom Scheme Proposed in 1969 by Robert Whittaker Monera Protista Fungi Plantae Animalia

Three-Domain Classification Favored by microbiologists EUBACTERIA ARCHAEBACTERIA EUKARYOTES

Six-Kingdom Scheme EUBACTERIA ARCHAEBACTERIA PROTISTA FUNGI PLANTAE ANIMALIA

Transitional Forms Dromaeosaurus Archaeopteryx