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Evolution
 

Evolution

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    Evolution Evolution Presentation Transcript

    • Evolution Biology S.Rucker
    • What scientific explanation can account for the diversity of life?  Biodiversity- the degree of variety of life. Where do these differences stem from?  The differences in these organisms stem from differences in their DNA (genetic diversity).  Genetic diversity- differences in DNA among the same species of a population resulting in different physical characteristics Ex- why are these puppies all colored differently even though they are littermates?
    • Evolution  Evolution, or change over time in a population, 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.  Evolution does not explain the origin of life itself.
    • So how does evolution happen?  Two hypotheses: J.B. Lamarck: Theory of Acquired Characteristics Published 1809 – same year Darwin and Abraham Lincoln were born. 1st “complete” theory of evolution Charles Darwin: Theory of Natural Selection Published in On the Origin of Species in 1859.
    • Jean-Baptiste Lamarck 1744-1829  Proposed the Theory of Acquired CharacteristicsBy selective use or disuse of organs, organisms acquired (gained) or lost certain traits during their lifetime. These changes were then passed on to their offspring. Over time, this process led to change in a species.
    • Lamarck’s Giraffe Example
    • Charles Darwin  Known as the “father” of evolution  Proposed that evolution happens by “natural selection” or survival of the fittest  Born in England (Feb. 12, 1809)  Left England on a ship known as the HMS Beagle in 1831 for a voyage around the world  Made observations on the Galapagos islands  Darwin was the “first” to “discover” why evolution happens. He published his ideas in a book called On the Origin of Species by Natural Selection in 1859
    • Galapagos Islands
    • 620 miles
    • Galapagos Islands A group of islands located ~1,000 km (around 620 miles) west of South America Islands very close together but had very different climates and different types of food sources Darwin studied ground tortoises , iguanas, and finches
    • 1 mile
    • Giant Tortoises of the Galápagos Islands Pinta Pinta Island Tower Marchena Intermediate shell Fernandina James Santa Cruz Isabela Santa Fe Hood Island Floreana Isabela Island Dome-shaped shell Hood Saddle-backed shell
    • Darwin’s ideas Discussed how organisms evolved from other organisms and how new species formed from “common ancestors” Ex- the lion, tiger, panther, bobcat and common house cat all descended or “came from” a common ancestor Ex- Tigers, dogs, horses, and bats share a common ancestor because they are all mammals
    • Darwin’s theory of evolution by natural selection 1. In nature, there is a struggle for existence, meaning that there is competition between each species for resources such as food, water, shelter, and space; in the same species there is competition for mates Ex- In predators, such as wolves, the wolf that has the ability to catch more rabbits will survive and reproduce more Ex- In prey, such as rabbits, that rabbits are faster, better camouflaged, etc. and will survive
    • Natural Selection Natural selection-Individuals that are better adapted and more “FIT” will survive and reproduce more successfully.  aka “Survival of the fittest”
    • 5 points of Darwin’s Theory of Natural Selection 1. There is genetic variation within populations 2. Some variations serve an organism better than others 3. More young are produced in each generation than can survive 4. Those that survive and reproduce must be those with better variations 5. Over enormous spans of time, small changes gather and populations change to the point of forming new species.
    • So what makes some organisms “better” than others? An adaptation is a genetic change within a new species that increases its fitness Ex- long legs, camouflage, jumping ability, etc Fitness is defined as an organism’s chances of survival until it can reproduce Depends on factors such as • Mating success • Avoiding predators • Finding food Which one of these moths would be considered more “fit” for this environment? Influenced by physical traits (adaptations) AND behavior.
    • Bill Gates, Microsoft CEO Brad Pitt, Actor
    • How quickly does evolution happen? Ideas differ based on the rate of change Gradualism – evolution occurs slowly but steadily over time Darwin and Lamarck believed this Punctuated Equilibrium – organisms change rapidly in bursts, followed by time unchanged Proposed by Steven Jay Gould (1941-2002)
    • Gradualism Change Time
    • Punctuated Equilibrium Change Time
    • But evolution was not Darwin’s Idea…He just figured out how it worked (the mechanism)  Evolutionary thought (and Darwin) was influenced by many individuals James Hutton (1785): Geologist estimating Earth to be millions of years old Thomas Malthus (1798): Economist studying interplay between population size and available resources J.B. Lamarck (1809): Proposed a flawed mechanism for how organisms change.
    • Agreements and Disputes The scientific community agrees that… Species change over time because of heritable traits Present-day organisms have descended from ancestors from the past Evolution occurs by natural selection The Earth is 4.6 billion years old Many scientists disagree about… The rate at which evolution occurs The exact ancestral relationships of species
    • Evidence of Evolution Can be found in:  fossils  geographic distribution of living species  embryology  Homologous structures Vestigial structures Biochemical similarities
    • 1. Fossils  Paleontologists study fossils.  Fossil – any evidence of an organism that is dead now. Can be mineralized pieces of the organism (often bones or shells), footprints, tunnels from burrowing creatures Fossils show, beyond any doubt, that life on Earth has changed over time.
    • How mammals adapted to life in the sea – whale evolution! Important changes: * Pelvis and hind-limbs reduced * Tail lengthened for swimming * Jaws modified for feeding on plankton
    • Dating Fossils & the Earth Two methods for determining age of objects: Radiometric dating – gives an approximate age (in years) by analyzing the presence of radioactive isotopes in the sample Eg) Carbon dating measures C-14; often used on fossils Eg) Dating rocks on Earth has led to our estimate of the Earth’s age – 4.6 billion years. Relative dating – requires 2 objects; can only tell which is older or younger than the other by comparing their positions in the ground. Eg) Fossils in deeper strata (rock layers) are older than those found in strata above it.
    • In the strata of your laundry hamper…or bedroom floor… Where are the clothes you wore yesterday? The day before? And before that? And before that?
    • Why are there “gaps” in the fossil record? Not all organisms fossilize Natural processes destroy fossils Conditions are rarely suitable for fossilization when an organism dies They are often buried and hard to find Fossils (blue) will rarely be on the direct line of descent to present-day species (red).
    • Which strata is older? A B If we found fossils in Layer A and Layer B, which fossils are older?
    • 2) Geographic Distribution of Living Species  Similar species exist in different geographic locations  Ex. Beaver, muskrat, cap ybara, and coypu are all similar species that are found in both N. America and S. America (suggested continents were once close) Beaver Muskrat Beaver and Muskrat Coypu Capybara Coypu and Capybara
    • 3) Homologous Structures  Structures on different species that developed from the same body part  Ex. The flippers on a dolphin developed from the same body part as the arms of humans
    • Divergence results in homologous structures  Homologous structure- Structures with different mature forms but develop from the same embryonic tissue because they have a common evolutionary origin. Eg) Vertebrate limbs Whale flippers, frog forelimbs, and your own human arm most likely evolved from the front flippers of an ancient jawless fish. Turtle Alligator amphibian Ancient fish Bird Mammal
    •  The picture above shows part of the pectoral girdle and limb of two flying vertebrates known as the bat and the prehistoric pterosaur. Which bone of the pterosaur corresponds to the humerus of the bat?
    • 4. Comparative Anatomy: Vestigial Structures  Vestigial structure (or organ)- Features that have lost all or most of their original function and are similar to structures possessed by ancestral organisms.  These are remnants of more developed structures that were present and functional in ancestors.  Important: vestigial structures are not always “useless” – they often have reduced functions that are not essential for survival  Humans: appendix, coccyx (tail-bone), body hair, wisdom teeth, muscles that move our ears  Whales and pythons: hind-limb bones  Pigs: toes that do not touch the ground  Wingless birds: vestigial wing bones  Blind, burrowing or cave-dwelling animals: nonfunctioning eyes.
    • Hind-limb bones in a whale (top) and python (right).
    • Vestigial hind-limbs of a snake
    • Flightless Cormorants (Nannopterum harrisi) live on the Galápagos Islands. They must have been able to fly at some time in their history, but now they have only vestigial wings, which when held out to dry in typical Cormorant style, look tatty and pathetic. These vestigial wings do not help them when swimming (they move through the water by kicking their powerful feet), but they are thought to help them to keep balance when hopping between rocks.
    • The Kiwis: New Zealand’s wingless group of birds – not the fruit! The wings are not quite absent, as the name implies, but are extremely aborted, consisting of a rudimentary humerus and one complete digit.
    • 5) Embryology  In early stages of development, or embryos, many animals with backbones are very similar
    • 6. Biochemical Evidence for Evolution (DNA similarities) All organisms made of the same basic molecules (proteins, carbohydrates, lipids, nucleic acids) All organisms based on the same, universal genetic code. The more closely related one species is to another, the more similarities should be observed in their biochemical makeup DNA sequences Amino acid sequences of proteins
    • Evolution of a Cell
    •  One method of determining the classification of an animal is comparing the amino acid sequence.
    • Convergent vs Divergent Evolution
    • Divergent Evolution  Divergent evolution (aka. speciation)- when a group from a specific population accumulates enough changes that it becomes a new species and is reproductively isolated (cannot interbreed) from its ancestors.  A species is a group of organisms that can breed and produce fertile offspring.  A population is a group of individuals of the same species that can breed.  Organisms that have recently “diverged” share many characteristics, but are too different to interbreed. Organisms that diverged a long time ago have fewer characteristics in common.  Homologous structures are produced by divergence.
    • Causes of divergence in species  Mutation as the cause of divergenceSometimes mutations in the population cause changes in the gene pool resulting in the emergence of new species  but this is rare!  Ex- a bacterial cell mutates into a new species- MRSA vs Staph aureus
    • Isolation leads to Divergence  Different types of isolation:  1) Geographic isolation – when populations become physically separated & unable to reproduce  Such as the storm-blown finches on the Galapagos  Continental movement, sea level changes, mountain range formation, new rivers, etc.  Sometimes referred to as reproductive isolation because two species can’t physically come together to mate due to geographical barrier (like the grand canyon)
    • Isolation (cont.) Sources of isolation 2) Behavioral isolation –two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior. These meadowlarks have overlapping ranges but do not interbreed because they have different mating songs. Each population will evolve independently and slowly accumulate more differences. Eastern Meadowlark Western Meadowlark
    • Isolation (cont.) Sources of isolation: 3) Temporal isolation – individuals mate at different times of the year. Ranges overlap, but they do not mate at the same time of year! Eastern Spotted Skunk (mates late winter) Western Spotted Skunk (mates late summer)
    • Adaptive Radiation  Adaptive radiation – When a single species diverges rapidly into several different species which all “occupy” different niches.  Niche – an organism’s role in it’s environment When 2 organisms occupy the same niche, competition arises. Darwin noticed adaptive radiation in finches on the Galapagos Islands.
    • Hypothesis: Ancestral finch species blown over to the Galapagos Islands from South America during a hurricane. In a brand new environment, the finches rapidly adapted to exploit available food sources.
    • Answer these questions????  An organism’s job is called its _______.  How many different niches do you observe from Darwin’s finch diagram?
    •  The finches of Galapagos islands were separated by very little distance. However, there were many different species of finches with different beak size and shape that evolved from a common finch. What can account for the different species of finches?  A) closeness of islands  B) many predators  C) different available food  D) each island has a different climate  The island of Tasmania is off the coast of Australia. It is home to the Tasmanian Devil. The Tasmanian Devils on Tasmania are very different from its cousin on the mainland of Australia. What can account for these differences?
    • Convergent Evolution Convergent evolution – process in which species that are not closely related to each other independently develop similar traits. Eg) Butterflies, hawks, and bats all have wings. NOT due to a common ancestor passing a “wing” gene to each Each kind of wing evolved independently, suggesting that the trait of flight is useful for the purpose of survival and reproduction. These wings are considered to be analogous structures.
    • Analogous Structures A result of convergent evolution, analogous structures look and function similarly but do not share a common evolutionary history. Eg) Wings. These structures perform the same function (flight), but they evolved independently. “Hummingbird moth” (an insect) “Hummingbird” (a bird)
    • Streamlined bodies and various appendages for moving quickly through water… Yet a shark is a fish… Penguins are birds… And dolphins are mammals. These features evolved independently in response to the selective pressures of a marine life.
    • Magnified by SEM Koala Human
    • Types of Evolution & Supporting Evidence  Fossil Record  Biochemistry  Comparative Anatomy  Divergent evolution  Homologous Structures  Adaptive Radiation  Convergent Evolution  Analogous Structures  Vestigial Structures  Embryology