Evolution Descent with Modification: A Darwinian View of Life
Evolution Evolution: the change over time of the genetic composition of populations Natural selection: populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success) Evolutionary adaptations: a prevalence of inherited characteristics that enhance organisms survival and reproduction
Charles Darwin 1809-1882 British naturalist Proposed the idea of evolution by natural selection Collected clear evidence to support his ideas
Voyage of the HMS Beagle Invited to travel around the world 1831-1836 (22 years old!) makes many observations of nature main mission of the Beagle was to chart South American coastline Stopped in Galapagos Islands 500 miles off coast of Ecuador
Darwin found birds Collected many different birds on the Gaapagos Islands. Finch? Sparrow? Thought he found very different kinds Woodpecker? Warbler?
But Darwin found a lot of finches Darwin was amazed to find out: All 14 species of birds were finches Large Ground Finch Small Ground Finch But there is only one species of finch on the mainland! Veg. Tree Finch Warbler Finch
Darwin s finches Differences in beaks associated with eating different foods survival & reproduction of beneficial adaptations to foods available on islands Warbler finch Cactus finch Woodpecker finch Sharp-beaked finch Small insectivorous tree finch Large insectivorous tree finch Vegetarian tree finch Insect eaters Bud eater Cactus eater Seed eaters Small ground finch Medium ground finch Large ground finch
Darwin s finches Darwin s conclusions small populations of original South American finches landed on islands variation in beaks enabled individuals to gather food successfully in the different environments over many generations, the populations of finches changed anatomically & behaviorally accumulation of advantageous traits in population emergence of different species
Darwin s finches Differences in beaks allowed some finches to successfully compete successfully feed successfully reproduce pass successful traits onto their offspring
More observations Correlation of species to food source
Many islands also show distinct local variations in tortoise morphology perhaps these are the first steps in the splitting of one species into several?
Unique species
Anaerobic Bacteria Photosynthetic Bacteria Dinosaurs Green Algae Multicellular Animals Flowering Molluscs Arthropods Chordates Jawless Fish Teleost Fish Amphibians Insects Reptiles Mammals Birds Land Plants Seed Plants Plants mya Quaternary 1.5 Tertiary 63 Cretaceous 135 Jurassic 180 Triassic 225 Permian 280 Carboniferous 350 Devonian 400 Silurian 430 Ordovician 500 Cambrian 570 Ediacaran 700 Precambrian, Proterozoic, & Archarozoic 4500 Life s Natural History is a record of Successions & Extinctions
Life has changed over time & in turn has changed the Earth Living creatures have changed Earth s environment making other life possible
In historical context Other people s ideas paved the path for Darwin s thinking competition: struggle for survival population growth exceeds food supply land masses change over immeasurable time
A Reluctant Revolutionary Returned to England in 1836 wrote papers describing his collections & observations long treatise on barnacles draft of his theory of species formation in 1844 instructed his wife to publish this essay upon his death reluctant to publish but didn t want ideas to die with him
And then came the letter. Then, in 1858, Darwin received a letter that changed everything Alfred Russel Wallace a young naturalist working in the East Indies, had written a short paper with a new idea. He asked Darwin to evaluate his ideas and pass it along for publication.
The time was ripe for the idea! To Lyell
November 24, 1859, Darwin published Voyage: 1831-1836 On the Origin of Species by Means of Natural Selection http://www.pbs.org/wgbh/evolution/library/02/2/l_022_04.htl Darwin: Reluctant Rebel
Essence of Darwin s ideas Natural selection variation exists in populations over-production of offspring more offspring than the environment can support competition for food, mates, nesting sites, escape predators differential survival successful traits = adaptations differential reproduction adaptations become more common in population
Lamarck Organisms adapted to their environments by acquiring traits change in their life time Disuse organisms lost parts because they did not use them like the missing eyes & digestive system of the tapeworm Perfection with Use & Need the constant use of an organ leads that organ to increase in size like the muscles of a blacksmith or the large ears of a night-flying bat transmit acquired characteristics to next generation
Lamarckian vs. Darwinian view Lamarck in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring Darwin giraffes born with longer necks survive better & leave more offspring who inherit their long necks
Evidence supporting evolution Fossil record transition species Anatomical record homologous & vestigial structures embryology & development Molecular record protein & DNA sequence Artificial selection human-caused evolution
Evolution evidence: The Fossil Record Succession of forms over time Transitional links Vertebrate descent
Fossil record Layers of sedimentary rock contain fossils new layers cover older ones, creating a record over time fossils within layers show that a succession of organisms have populated Earth throughout a long period of time
Fossil Record
Fossil record A record showing us that today s organisms descended from ancestral species
Fossil record OBSERVATION
Land Mammal????
2006 Fossil Discovery of Early Tetrapod Tiktaalik missing link from sea to land animals
Evolution evidence: Comparative Anatomy Homologous structures (homology) Descent from a common ancestor
Anatomical record Homologous structures similarities in characteristics resulting from common ancestry
Homologous structures Similar structure Similar development Different functions Evidence of close evolutionary relationship recent common ancestor
colored leaves Homologous structures spines leaves succulent leaves needles tendrils
Analogous structures Separate evolution of structures similar functions similar external form different internal structure & development different origin no evolutionary relationship Solving a similar problem with a similar solution
Vestigial organs Modern animals may have structures that serve little or no function remnants of structures that were functional in ancestral species deleterious mutations accumulate in genes for noncritical structures without reducing fitness snakes & whales remains of pelvis & leg bones of walking ancestors eyes on blind cave fish human tail bone This is not LaMarck s loss from disuse!
Vestigial organs Hind leg bones on whale fossils Why would whales have pelvis & leg bones if they were always sea creatures?
Evolution evidence: Biogeography Geographical distribution of species Examples: Islands vs. Mainland Australia Continents
Evolution evidence: Comparative Embryology Pharyngeal pouches, tails as embryos
Comparative embryology Reveals additional anatomical homologies not visible in adult organisms Pharyngeal pouches Post-anal tail Chick embryo Figure 22.15 Human embryo
Evolution evidence: Molecular Biology Similarities in DNA, proteins, genes, and gene products Common genetic code Closely related species have sequences that are more similar than distantly related species DNA & proteins are a molecular record of evolutionary relationships
Building family trees Closely related species (branches) share same line of descent until their divergence from a common ancestor
Artificial selection Artificial breeding can use variations in populations to create vastly different breeds & varieties
Natural selection in action Insecticide & drug resistance insecticide didn t kill all individuals resistant survivors reproduce resistance is inherited insecticide becomes less & less effective
Convergent evolution Flight evolved in 3 separate animal groups evolved similar solution to similar problems analogous structures Does this mean they have a recent common ancestor?
Convergent evolution Fish: aquatic vertebrates Dolphins: aquatic mammals similar adaptations to life in the sea not closely related Those fins & tails & sleek bodies are analogous structures!
Parallel types across continents Niche Placental Mammals Australian Marsupials Burrower Anteater Nocturnal insectivore Mole Anteater Mouse Marsupial mole Numbat Marsupial mouse Climber Glider Stalking predator Lemur Flying squirrel Ocelot Spotted cuscus Sugar glider Tasmanian cat Chasing predator Wolf Tasmanian wolf
Parallel Evolution Convergent evolution in common niches filling similar ecological roles in similar environments, so similar adaptations were selected but are not closely related marsupial mammals placental mammals
Essence of Darwin s ideas (1) Variation exists in natural populations (2) Many more offspring are born each season than can possibly survive to maturity (3) As a result, there is a struggle for existence - competition (4) Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the average characteristics of the population - adaptations (5) Over long periods of time, and given a steady input of new variation into a population, these processes lead to the emergence of new species