Evolution, Darwin and Evidence 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 November 24, 1859

Evolutionary history Linnaeus: taxonomy Hutton: gradualism Lamarck: evolution Malthus: populations Cuvier: paleontology Lyell: uniformitarianism Darwin: evolution Mendel: inheritance Wallace: evolution

Charles Darwin 1809-1882 British naturalist Proposed the idea of evolution by natural selection Collected clear evidence to support his ideas What did Darwin say? What evidence supports Evolution by Natural Selection? What impact did Evolution have on biology?

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 After graduation Darwin was recommended to be the conversation companion to Captain Robert FitzRoy, preparing the survey ship Beagle for a voyage around the world. FitzRoy chose Darwin because of his education, his similar social class, and similar age as the captain. Darwin noted that the plants and animals of South America were very distinct from those of Europe

Darwin found… birds Collected many different birds on the Galapagos Islands. Thought he found very different kinds… Finch? Finch? Sparrow? Woodpecker? Warbler? Sparrow? Woodpecker? Warbler?

But Darwin found… a lot of finches Darwin was amazed to find out: All 14 species of birds were finches… But there is only one species of finch on the mainland! Large Ground Finch Small Ground Finch Sparrow? How did one species of finches become so many different species now? Warbler Finch Veg. Tree Finch Woodpecker? Warbler?

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 Small ground finch Warbler finch Large insectivorous tree finch Cactus eater Tree finches Medium ground finch Ground finches Insect eaters Seed eaters Vegetarian tree finch Large ground finch Bud eater

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

Seeing this gradation & diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species has been taken & modified for different ends.

Darwin’s finches Differences in beaks allowed some finches to… successfully compete successfully feed successfully reproduce pass successful traits onto their offspring

Correlation of species to food source More observations… Correlation of species to food source Whoa, Turtles, too!

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

Evolution evidence: Biogeography Geographical distribution of species Examples: Islands vs. Mainland Australia Continents

Evidence supporting evolution Fossil record transition species Anatomical record homologous & vestigial structures embryology & development Molecular record protein & DNA sequence Artificial selection human-caused evolution

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

Evolution evidence: The Fossil Record Succession of forms over time Transitional links Vertebrate descent

Fossil record A record showing us that today’s organisms descended from ancestral species

Evolutionary change in horses 550 500 450 Equus 400 350 Body size (kg) 300 250 Merychippus increase in size, loss of toes, increase in size of molars 20-25 mya grasslands became widespread in Norh America molars = easer to eat grass hoof = faster locomotion on grassland 200 Mesohippus 150 Hyracotherium 100 50 Nannippus 60 55 50 45 40 35 30 25 20 15 10 5 Millions of years ago

Evolution of birds Archaeopteryx lived about 150 mya links reptiles & birds The avian nature of the brain and inner ear of Archaeopteryx (Alonso et al. 2004) - Archaeopteryx, the earliest known flying bird from the Late Jurassic period, exhibits many shared primitive characters with more basal coelurosaurian dinosaurs (the clade including all theropods more bird-like than Allosaurus), such as teeth, a long bony tail and pinnate feathers. However, Archaeopteryx possessed asymmetrical flight feathers on its wings and tail, together with a wing feather arrangement shared with modern birds. This suggests some degree of powered flight capability but, until now, little was understood about the extent to which its brain and special senses were adapted for flight. Alonso et al. (2004) investigated this problem by computed tomography scanning and three-dimensional reconstruction of the braincase of the London specimen of Archaeopteryx. A reconstruction of the braincase and endocasts of the brain and inner ear suggest that Archaeopteryx closely resembled modern birds in the dominance of the sense of vision and in the possession of expanded auditory and spatial sensory perception in the ear. Alonso et al. (2004) concluded that Archaeopteryx had acquired the derived neurological and structural adaptations necessary for flight. An enlarged forebrain suggests that it had also developed enhanced somatosensory integration with these special senses demanded by a lifestyle involving flying ability. Smithsonian Museum, Washington, DC

Evolution evidence: Comparative Anatomy Homologous structures (homology) Descent from a common ancestor

Homologous structures Similar structure Similar development Different functions Evidence of close evolutionary relationship recent common ancestor

Analogous structures Separate evolution of structures similar functions similar external form different internal structure & development different origin no evolutionary relationship Don’t be fooled by their looks! 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 non-critical structures without reducing fitness snakes & whales — remains of pelvis & leg bones of walking ancestors eyes on blind cave fish human tail bone

Vestigial organs Hind leg bones on whale fossils

Evolution evidence: Comparative Embryology Pharyngeal pouches, ‘tails’ as embryos

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

Comparative hemoglobin structure Human Macaque Dog Bird Frog Lamprey 8 32 45 67 125 10 20 30 40 50 60 70 80 90 100 110 120 Number of amino acid differences between hemoglobin (146 aa) of vertebrate species and that of humans

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” “descendants” of the wolf

Natural selection in action Insecticide & drug resistance insecticide didn’t kill all individuals resistant survivors reproduce resistance is inherited insecticide becomes less & less effective The evolution of resistance to insecticides in hundreds of insect species is a classic example of natural selection in action. The results of application of new insecticide are typically encouraging, killing 99% of the insects. However, the effectiveness of the insecticide becomes less effective in subsequent applications. The few survivors from the early applications of the insecticide are those insects with genes that enable them to resist the chemical attack. Only these resistant individuals reproduce, passing on their resistance to their offspring. In each generation the % of insecticide-resistant individuals increases.

Final words…... “Absence of evidence is not evidence of absence.”