Chapter 17 Introduction to Darwinian Evolution Evolution Accumulation

Chapter 17: Introduction to Darwinian Evolution

Evolution • Accumulation of inherited changes within populations over time • NOT changes in an individual in its lifetime • Changes in characteristics of populations over many generations

2 perspectives: • 1) MICROEVOLUTION: short-term adaptations of population to changes in the environment • 2) MACROEVOLTUION: long-term formation of different species from common ancestors

Contributing Scientists • Jean Baptiste de Lamarck – 1 st – organisms undergo change because of natural phenomena – Organisms endowed with vital force to change toward complexity over time – Organisms could pass traits acquired during their lifetimes to their offspring • Giraffes – stretch necks • Discredited when basis for heredity discovered

• Thomas Malthus – Population growth not always desirable – Outstrip food supply – Famine, disease, war – stop growth • “struggle for existence” – strong and constant check on human population growth • Charles Lyell – Slow geological processes Old Earth

• Charles Darwin – HMS Beagle – South America – 5 years – Naturalist – plants, animals, fossils, geology – Galapagos Islands – compared species to mainland other Galapagos Islands – Artificial selection: breeders develop varieties in a few generations • Dogs, plants • Similar process in nature – model for natural selection

Fig. 22 -9 Terminal bud Cabbage Lateral buds Flower clusters Brussels sprouts Leaves Kale Cauliflower Stem Wild mustard Flowers and stems Broccoli Kohlrabi

Fig. 22 -5 GREAT BRITAIN EUROPE NORTH AMERICA ATLANTIC OCEAN AFRICA Pinta Marchena Santiago Fernandina Isabela Genovesa Daphne Islands Pinzón Santa Cruz Florenza Santa Fe PACIFIC OCEAN San Cristobal Española Equator SOUTH AMERICA AUSTRALIA Andes The Galápagos Islands Cape of Good Hope Tasmania Cape Horn Tierra del Fuego New Zealand

– Favorable variations would be preserved, unfavorable eliminated – adaptation : evolutionary modification that improves the chances of survival and reproductive success in a give environment – Accumulation of modifications maybe new species – Time required for new species to originate • Old Earth

Fig. 22 -6 (a) Cactus-eater (c) Seed-eater (b) Insect-eater

Fig. 22 -2 Linnaeus (classification) Hutton (gradual geologic change) Lamarck (species can change) Malthus (population limits) Cuvier (fossils, extinction) Lyell (modern geology) Darwin (evolution, natural selection) Wallace (evolution, natural selection) American Revolution French Revolution U. S. Civil War 1800 1900 1750 1850 1795 Hutton proposes his theory of gradualism. 1798 Malthus publishes “Essay on the Principle of Population. ” 1809 Lamarck publishes his hypothesis of evolution. 1830 Lyell publishes Principles of Geology. 1831– 1836 Darwin travels around the world on HMS Beagle. 1837 Darwin begins his notebooks. 1844 Darwin writes essay on descent with modification. 1858 Wallace sends his hypothesis to Darwin. 1859 The Origin of Species is published.

Natural Selection (Darwin) • Better adapted organisms are more likely to survive and become parents • Population changes over time; frequency of favorable traits increase with each generation

4 observation for Natural Selection • 1) Variation – each individual is unique – Some advantageous traits - inherited • 2) Overproduction – each species can produce more offspring than can survive • 3) Limits on Population Growth – (struggle for existence) more individuals than resources competition • 4) Differential reproductive success – (survival of the fittest) better adapted individuals will survive and reproduce

Fig. 22 -10

Evidence for Evolution • • • Fossil Record Comparative Anatomy Biogeography Developmental biology Molecular evidence

Fossil Record • Fossils – remains/traces of previously existing organisms – Sedimentary rock, bogs, tar, amber, ice – Conditions slow or prevent decay – Covered quickly – water, sand – Hard body parts – Record biased – location, body

Dating Fossils • 1) Relative Age – position in rock – Index fossils – • characterize a specific layer over large geographical areas • Existed short time, preserved in large numbers – With this info arrange rock layers and fossils in chronological order and identify comparable layers in widely separated locations

Fig. 22 -3 Layers of deposited sediment Younger stratum with more recent fossils Older stratum with older fossils

• 2) Absolute Age – – Radioisotopes – emit radiation – nucleus changes into nucleus of different element with decay – Half-life – time required for ½ of the atoms to change to a different atom – Potassisum-40 (1. 3 billion years) – Uranium-235 (704 million years) – Carbon-14 (5730 years)

Comparative Anatomy • Similar structures related organisms (common ancestor) • Homologous structures – features derived from same structure in a common ancestor – Ex: limb bones of mammals, modified leaves – Similar structure, different function • Homoplastic features (Analogous features) – structurally similar features that are not homologous but have similar functions in distantly related organisms – Ex: wings of insects/birds, spines and thorns – Same function, evolved separately (different structure)

Fig. 22 -17 Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat

Fig. 22 -20 Sugar glider NORTH AMERICA AUSTRALIA Flying squirrel

– Show organisms with separate ancestries may adapt in similar ways to similar environmental demands Convergent evolution • Ex: aardvarks, anteaters, pangolins • Vestigial structures – organs or parts of organs that are seemingly nonfunctional and degenerate, undersized or lacking some essential part – Remnants of parts that were functional in ancestors – Ex: • • • Human - appendix, coccyx, 3 rd molars, ear muscles Whales/pythons – hind limb bones Pigs – vestigial toes Kiwi – wingless bird – vestigial wing bones Burrowing/cave-dwelling – vestigial eyes Vestige usually not harmful so selective pressure to completely eliminate is weak

Biogeography • Study of past and present geographical distribution of organisms • Not all animals/plants found in all environments where they could survive • Spread from origin • Continental drift / Pangaea

Developmental biology • Genetic similarities reflect shared evolutionary history • Vertebrates – embryological development similar common ancestor – (segmentation, gill pouches, aortic arches)

Fig. 22 -18 Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo

Molecular evidence • Confirms structural and fossil evidence • Universal genetic code • Similar amino acid sequences, proteins, nucleotides • More similarities common ancestor • Phylogenetic trees - diagrams showing lines of descent – Derived from differences in DNA sequences – Whales and hippos closely related

Evolution is happening NOW! • Can be observed in our lifetime • Ex: – Resistant Bacteria – Finch beaks – Guppy study