2 15–1 The Puzzle of Life's Diversity This variety of living things is called biological diversity.How did all these different organisms arise? How are they related?Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms.A scientific theory is a well-supported testable explanation of phenomena that have occurred in the natural world.
3 Voyage of the BeagleCharles Darwin (born February 12, 1809 in England)1831 – set sail on the H.M.S. Beagle
4 During his travels, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.That hypothesis, now supported by a huge body of evidence, has become the theory of evolution.
5 On The Voyage Collected plants & animals on land At sea – studied specimens, read, recorded observationsSaw great diversity in the organisms – enormous numbers of species!
6 Patterns of DiversityPlants and animals seemed so well suited to their environmentsImpressed by the many ways organisms survive and reproduceSimilar areas on different continents were inhabited by very different animals.Ex: why are there no rabbits on the Australian grasslands? No kangaroos in England?
7 Living Organisms and Fossils Darwin also collected fossilsSome fossils looked like organisms that were still aliveOther fossils looked completely different!Darwin wondered:Why had so many of these species disappeared?How were they related to living species?
8 The Galápagos Islands 1000 km west of South America (Ecuador) Islands are close together but very different climatesDarwin was fascinated in particular by the land tortoises and marine iguanas
9 The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.
10 The Journey HomeDarwin began to wonder if animals living on different islands had once been members of the same species.these separate species would have evolved from an original South American ancestor species after becoming isolated from one another
11 15-2 Ideas that shaped Darwin’s thinking Geological InformationMassive, rich fossil record – much older than the current age of the earth beliefs.James Hutton (1795) – old earth – great earth changes take timeCharles Lyell (1831) – the processes shaping the Earth now are the same ones that shaped the earth in the pastCould life change as earth has changed?
12 Jean Baptiste Lamarck 1809 “living things have changed over time” Species descended from other speciesLamarck’s theory of evolution:Tendency toward perfectionUse and DisuseInheritance of Acquired TraitsWhy was he wrong?Behavior doesn’t affect the DNAHe was WRONG.
13 Thomas Malthus1798Population growth (if gone unchecked) would quickly over run the earthWhy don’t maple trees cover the earth since they each release 1000s of seeds?Darwin’s questions:What causes the deaths of so many?What factors determine which survive and reproduce?
14 All species tend to produce more offspring than they can support Turtle eggsInsect eggsFrog eggs
15 15-3 Darwin presents his case Worked for years but scared to publish because of religious backlash1858 – sent an essay by Alfred Russell Wallace summarizing Darwin’s theory of evolution1859 – Darwin publishes “On the origin of species by means of natural selection”
16 What did Darwin say? Inherited Variation & Artificial Selection Members of a species varyArtificial Selection = nature provides the variation and humans select the variations they find usefulExamples: fat hog, fast horse, high milk producing cowDoes something in nature select the same way?
19 Evolution by Natural Selection Compared nature to artificial selection
20 Struggle for Existence Members of each species compete for food, space, mates, and other necessities of lifePredators (that are better/faster) catch more preyPrey (faster, better camouflage) avoid being caughtExamples: fast cheetah, small rabbit, stronger lion, more colorful butterfly
21 Producing more offspring than can possibly survive thus creating a struggle for existing resources sunflowerPreying Mantis
22 Survival of the Fittest Fitness = being able to survive and reproduce in its specific environmentFitness results from adaptationsAdaptations = inherited characteristics that improve an organisms chance of survivalSuccessful adaptation better suited to the environment more fitness
23 Adaptations – Anatomical/structural (quills on a porcupine) Physiological (photosynthesis)Behavioral (live/hunt in groups)
24 Low Fitness organisms die off High Fitness survive + reproduce Survival of the Fittest!Natural Selection of most fit organisms!
25 Nature (the environment) will determine which organism is the fittest to Survive
26 Natural SelectionResults from NO human intervention, control, or directionResults in changes in the inherited characteristics of a populationIncreases a species’ fitness in the environment (over time!)
27 Descent with Modification Over large amounts of time… natural selection produces organisms:with different structuresestablishes different nichesoccupies different habitatsorganisms look different than their ancestorsDescent with modification = each living thing has descended with changes, from other species over time.
28 Common AncestorsImplies that organisms are all related to one another.Tiger, panther, cheetah – relatedHorses, dogs, cats – related farther backMammals, birds, reptiles, fish – related even farther backAll living things – related!Single Tree of Life!
31 Living things have been evolving on Earth for millions of years… Evidence..Fossil RecordGeographic distribution of living speciesHomologous body structuresbody part with the same basic structure and embryonic origin as that of another organism, though not necessarily sharing the same functionSimilarities in early development (embryology)
32 The Fossil Record Fossils = remains of ancient life Different layers of rock were formed at different times during Earth’s history.Darwin proposed that organisms had coming into being, lived, and vanished.Life had changed over time!
36 Since Darwin… The number of known fossils has gone up dramatically! Researchers have discovered many hundreds of transitional fossils that document various intermediate stages in the evolution of modern species from organisms that are now extinct.Gaps remain in the fossil recordsThese gaps do not indicate weakness in the theory of evolution itself. Rather, they point out uncertainties in our understanding of exactly how some species evolved.
37 Geographic Distribution of Living Species Darwin wondered about the finches he found in the Galapagos Islands.Where were they similar but still different?Also.. Slightly different from S. American mainland speciesCould the birds have changed as they adapted to local environments?=> descended with modification from a common mainland ancestor
38 Convergent EvolutionDarwin found entirely different species of animals on the continents of South America and Australia.Similar environments on those continents he sometimes saw different animals that had similar anatomies and behaviors.The existence of similar but unrelated species was a puzzle to Darwin.
40 Convergent EvolutionThe adaptive evolution of superficially similar structures, such as the wings of birds and insects, in unrelated species subjected to similar environments.
41 Unrelated organisms come to resemble one another
42 Analogous StructuresStructures that serve the same function in different species but they evolved independentlysame function, different structureEx: bat wing, butterfly wing
43 Divergent Evolutiontwo or more related species becoming more and more dissimilar
44 Homologous Body Structures striking anatomical similarities among the body parts of animals with backbonesof reptiles, birds, and mammals—arms, wings, legs, and flippers—vary greatly in form and function.all constructed from the same basic boneslimbs has adapted in ways that enable organisms to survive in different environments
45 Homologous Body Structures structures that have different mature forms in different organisms but develop from the same embryonic tissues
46 Vestigial Organs organ that serves no useful function in an organism Why would an organism possess organs with little or no function?One possibility = presence of a vestigial organ may not affect an organism's ability to survive and reproduce natural selection would not cause the elimination of that organ.
48 The human appendixhas no function inhumans but is veryimportant in cows andother animals
49 Human tailbone is a vestigial vertebrate tail consists of fusedvertebrae that nolonger functionas a tail
50 Similarities in Embryology embryos of many animals with backbones are very similarmany embryos look especially similar during early stages of development
51 chickens, turtles, and rats Pharyngeal slitsDolphin
52 Summary of Darwin's Theory Individual organisms differ, and some of this variation is heritable.Organisms produce more offspring than can survive, and many that do survive do not reproduce.Because more organisms are produced than can survive, they compete for limited resources.
53 Each unique organism has different advantages and disadvantages in the struggle for existence. Individuals best suited to their environment survive and reproduce most successfully. These organisms pass their heritable traits to their offspring. Other individuals die or leave fewer offspring. This process of natural selection causes species to change over time.Species alive today are descended with modification from ancestral species that lived in the distant past. This process, by which diverse species evolved from common ancestors, unites all organisms on Earth into a single tree of life.