1 / 44

Evolution by Natural Selection

Evolution by Natural Selection. Chapter 23. Darwin’s Theories. Charles Darwin. While on the voyage of the HMS Beagle in the 1830s, Charles Darwin went onshore and collected thousands of specimens of fossils and living things By studying these specimens he observed:

Lucy
Download Presentation

Evolution by Natural Selection

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Evolution by Natural Selection Chapter 23

  2. Darwin’s Theories

  3. Charles Darwin • While on the voyage of the HMS Beagle in the 1830s, Charles Darwin went onshore and collected thousands of specimens of fossils and living things • By studying these specimens he observed: • similarities between living and fossil organisms • the diversity of life in the world including the Galápagos Islands, where there was great diversity

  4. Charles Darwin • Darwin became convinced that the Earth was old and continually changing • He concluded that living things also change, or evolve over generations • He also stated that living species descended from earlier life-forms: descent with modification

  5. Darwin’s Theories • Natural selection- populations change over generations if individuals that possess certain traits have differential breeding success • Result is evolutionary adaptation where accumulated traits enhance an organisms ability to survive • Results in evolution, where a change in a populations genetic composition occurs over time

  6. Pre Darwin Theories • Until Darwin came up with his theories, most ideas viewed species as fixed and unchanging • Bible states that all animals were made perfect by God and never change • Carolus Linnaeus • Interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose • Was a founder of taxonomy, classifying life’s diversity “for the greater glory of God”

  7. Some Theories that Darwin Built Upon • Taxonomy influenced Darwin and helped to reinforce Darwin’s theories • The study of fossils also helped to lay the groundwork for Darwin’s ideas • Usually found in sedimentary rock, which appears in layers or strata • The theory of gradualism is the idea that profound change can take place through the cumulative effect of slow but continuous processes • Helped Darwin show how old the earth could be • Lamarck used observations in nature to develop his theories of acquired characteristics

  8. Darwin’s Voyage • In 1831, after college, Darwin was accepted on board the HMS Beagle, which was about to embark on a voyage around the world • During his travels on the Beagle Darwin observed and collected many specimens of South American plants and animals • Darwin observed various adaptations of plants and animals that inhabited many diverse environments

  9. England EUROPE NORTH AMERICA ATLANTIC OCEAN PACIFIC OCEAN HMS Beagle in port Galápagos Islands AFRICA SOUTH AMERICA Darwin in 1840, after his return AUSTRALIA Cape of Good Hope Andes Tasmania Cape Horn New Zealand Tierra del Fuego Darwin’s Voyage

  10. The Origin of Species • After the voyage, in 1844, Darwin wrote a long essay on the origin of species and natural selection • But he was reluctant to introduce his theory publicly, anticipating the uproar it would cause • In June 1858 Darwin received a manuscript from Alfred Russell Wallace • Who had developed a theory of natural selection similar to Darwin’s • Darwin quickly finished The Origin of Species • And published it the next year

  11. The Origin of Species • Darwin made two major points in his book • He presented evidence that the many species of organisms presently inhabiting the Earth are descendants of ancestral species • He proposed a mechanism for the evolutionary process, natural selection

  12. Descent with Modification • Darwin believed: • There was a unity to life • That all organisms were related through descent with modification from an ancestor that lived in the remote past • Called descent with modification • Organisms developed diverse modifications to adapt to specific ways of life

  13. Sirenia (Manatees and relatives) Loxodonta africana (Africa) Elephas maximus (Asia) Loxodonta cyclotis (Africa) Hyracoidea (Hyraxes) Years ago Stegodon Mammut Mammuthus Deinotherium Platybelodon Millions of years ago Barytherium Moeritherium Descent with Modification • In the Darwinian view, the history of life is like a tree • With multiple branches from a common trunk to the tips of the youngest twigs that represent the diversity of living organisms

  14. Evidence of Change Over Time

  15. Evidence for Changethrough Time • Fossils are traces of organisms that lived in the past • Fossils found and described in the scientific literature make up the fossil record

  16. Evidence for Changethrough Time • Most fossils are found in sedimentary rocks • Layers of sedimentary rock are associated with different intervals in the geologic time scale • A relative time scale based upon fossil content

  17. Carbon 14 Dating • Use radioactive isotopes to assign absolute ages • Carbon 14 • Uranium • Find out the amount of the product left • Earth is about 4.6 billion years old • Earliest signs of life at about 3.85 billion years old

  18. Fossils • Many fossils provide evidence for extinct species unlike any known living organisms • May link present organisms to past organisms

  19. Transitional Forms • The law of succession means that extinct fossil species are typically succeeded, in the same region, by similar species • Darwin saw this as evidence that species change over time

  20. Transitional Forms • Transitional forms have been discovered with traits that are intermediate between older and younger species

  21. Vestigial Traits • Functionless structures that are similar to functioning structures in related species • Evidence that trait structure and function change over time

  22. Evidence That Species are Related

  23. Decent with Modification • Darwin found many types of mockingbird • Superficially similar, but different islands had distinct species • Descended with modification from a common ancestor

  24. Decent with Modification

  25. Decent with Modification

  26. Structural Homologies • Morphological traits that are similar • Same general limb structure in vertebrates

  27. Developmental Homologies • Similarity in embryo morphology and/or pattern of tissue differentiation • All vertebrates have gill pouches and tails early in embryonic development

  28. Developmental Homologies • Observed at two levels: • Overall morphology of embryos • Fate of particular embryonic tissues • Pattern exists because the common ancestor of all vertebrates was a fishlike animal with gill pouches and a tail

  29. Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide Species 100% Human Rhesus monkey 95% Mouse 87% Chicken 69% Frog 54% 14% Lamprey Genetic Homologies • Similarity in the DNA sequences of genes from different species • Result in structural homologies • Reflected in their molecules, their genes, and their gene products

  30. Human Rhesus monkey Mouse Chicken Frog Lamprey Last commonancestor lived26 million yearsago (MYA),based onfossil evidence 80 MYA 275 MYA 330 MYA 450 MYA Genetic Homologies

  31. Homology vs Analogy • Homology - similarities due to common descent • Analogy – similarities not due to descent • Due to environment • Convergent evolution occurs when natural selection leads to similar solutions to the challenges posed by a particular habitat

  32. The Process of Evolution

  33. How does natural selection work? • A population experiences natural selection whenever the following four conditions apply: (1) individuals vary in their traits (2) some of these variations are heritable (3) some individuals survive and reproduce better than other individuals (4) differential survival and reproduction

  34. Heritable Traits • Some traits help an individual survive or reproduce • These traits will, over time, increase in frequency in the population, causing evolution • An adaptation is a heritable trait that increases an individual's fitness in a particular environment

  35. Evolution and Natural Selection • Evolution is the result of natural selection • Natural selection is the mechanism for evolution • Individuals do not change during natural selection • Causes them to produce more offspring • Causes a change in the genetic makeup of the population • Shifts gene frequency

  36. Evolution • Evolution is not progressive, there are no higher or lower forms • There is no ultimate being to achieve • Forms can be older or younger • Adaptations are for a particular environment

  37. Evolution

  38. Evolution • Adaptation is not perfect • Not all traits are adaptive • Some give no effect • Structures that currently function in organisms may be subject to genetic or historical constraints • Subject to time and place

  39. Genetic and Historical Constraints • Genetic outcomes are limited to alleles in the population • Can be constrained by lack of genetic variation • Can only evolve from preexisting traits • Mutations of existing traits

More Related