Evidence for Biological Change––#

EVIDENCE FOR BIOLOGICAL CHANGE

  1. Introduction

    1. Theories of biological change (transmutation or evolution) did not develop without reason
    2. Theorists from Lamarck, to Darwin, to Gould have marshaled considerable evidence to support their contention that species are not fixed
    3. Here we will examine some of that evidence
    4. But first we will examine concepts of species fixity

  2. Fixity of species

    1. During the mid-1700’s and before, most thinking people believed that God had specially created each type of organism we see today––The “fixity of species” concept
    2. Some believed in a ladder of life

      1. “There is in this Universe a Stair rising not disorderly, or in confusion, but with a comely method and proportion” wrote Sir Thomas Browne
      2. All earthly and heavenly things were links in the Great Chain of Being spoken into existence by the Creator: Minerals > plants > animals > humans > cherubim > seraphim > God
      3. Links were of equal length
      4. Scythian lamb linked vegetable and animal worlds
      5. Homo duplex bridged a temporal earth with an eternal heaven Everything had a preordained place

    3. Not only did every created thing have its preordained place, but extinction was impossible––obviously God could not allow anything he had created to disappear, else the Chain of Being would be broken

  3. Questions raised

    1. During the Renaissance, people began to

      1. Travel widely
      2. Question earlier assumptions

    2. A significant body of knowledge about the natural world was assembled
    3. By the beginning of the 19th century, the fixity of species notion was in serious difficulty because of three emerging views:

      1. Ancient earth––Hutton and other students of geology began to suspect that the earth was much older than 6000 years
      2. Extinction––Cuvier and others demonstrated from fossils that extinction had occurred
      3. Transmutation––Several lines of evidence began to suggest that organisms had changed over time

  4. Evidence for biological change

    1. Diversity of life

      1. Over 1.5 million species of organisms have been cataloged
      2. May be as many as 30 to 50 million species on the planet
      3. Specific examples:

        1. 7,000 species of green algae
        2. 25,000 species of mushrooms and toadstools
        3. 13,000 species of flatworms
        4. 47,000 species of mollusks

      4. Someone once asked J. B. S. Haldane what he had learned about the mind of God after his years of study of biology. His reply: “Madam, only that he had an inordinate fondness for beetles”––There are 300,000 described species within this order of insects
      5. The fossil record shows that many more species lived in the past than are alive today
      6. Also, similar, seemingly closely related, organisms are restricted to certain areas of the world:

        1. More than 300 species of hummingbirds, restricted to the New World
        2. Scores of species of marsupials, most restricted to Australia
        3. Originally 22 species of Hawaiian honeycreepers, restricted to the Hawaiian islands
        4. Thirteen species of Galapagos finches, restricted to the Galapagos islands

      7. Why would God create such a diversity of similar organisms in the same regions of the world?

    2. Parasitism

      1. Ticks, mites, and mosquitoes
      2. Acanthocephalon (spiny-headed) worms

        1. 500 species described––undoubtedly there are many more that remain undescribed
        2. All are parasitic, with highly modified structures for infecting and eating their prey alive:

          1. Proboscis covered with curved spines for attachment to the digestive tracts of host
          2. Proboscis retractable into protected sheath when not in use

      3. Ichneumon wasps

        1. Constitute a huge family of insects––3,000 species in North America alone
        2. There are more species of ichneumons in the world than all the species of fish, amphibians, reptiles, birds, and mammals combined
        3. All ichneumons are parasitic as larvae:

          1. After mating, the adult female locates a species-specific host––often a caterpillar or aphid––for her young
          2. She stings the host, thus paralyzing it
          3. She, then, deposits her fertilized eggs on or in the body
          4. Eggs hatch into voracious larvae
          5. Larvae feast first on paralyzed host’s nonvital fat bodies and digestive structures
          6. Only then do they devour the life-supporting nervous and circulatory systems
          7. The young ichneumons finally emerge from a hollow corpse––having dined on living, quivering flesh to almost the last bite

      4. Why would a benevolent God have created creatures like parasites?

    3. Dulosis––slave-making among ants

      1. Many species of ants invade the colonies of other species and kill both the workers and the queen
      2. Young are captured and carried back to the invaders’ nest.
      3. There they are raised to adulthood and put to work foraging, nest- building, and caring for their captors young
      4. Slave-makers typically possess large mandibles for puncturing the heads of their opponents during raids
      5. Does slave-making seem like something God would have designed?

    4. Homologous structures

      1. Homologous structures have shared developmental pathways, but may serve quite different functions:

        1. Human forearm
        2. Foreleg of a horse
        3. Wing of a bird
        4. Wing of a bat
        5. Flipper of a seal

      2. Descent from a common ancestor seemed like the most parsimonious explanation for homologous structures
      3. If God had created all these organisms separately, why would he have used the same basic design for all of them?

    5. Vestigial structures

      1. Vestigial structures are anatomical units with no apparent function

        1. Salamanders

          1. Many salamanders have four functional legs
          2. Others have no legs
          3. Still others have only front legs by which they drag themselves along
          4. And still others have four legs, though only the front two are functional––the remaining vestigial legs drag helplessly along behind

        2. Whales

          1. Modern whales have useless, poorly-developed pelvic and femur bones “floating” in the hindquarters
          2. Fossil whales from the Eocene have functional pelvic and femur bones

      2. Why would God have created organisms with functionless structures?

    6. Imperfections

      1. Examples

        1. Tree kangaroos of New Guinea
        2. Terrestrial locomotion by sea mammals
        3. Sea otters
        4. Elephant seals
        5. Panda’s thumb

      2. Would God have designed things so poorly?

    7. Mimicry and deception

      1. Examples

        1. Deadly allure

          1. Orchid mantis
          2. Bird-dropping spider
          3. Lightning beetles

        2. Wolf-in-sheep’s-clothing strategy––Crysopid larval

      2. What kind of God would have ordained structures and behaviors that involved deadly deception?

    8. Fossil record

      1. Increase in the percent of extinct types as strata get older
      2. Apparent changes within lineages:

        1. Reptiles > mammals
        2. Reptiles > birds
        3. Toothed > nontoothed birds
        4. Multiple-toed horses > single-toed horses

      3. The fossil record seemed to clinch the conclusion that extinction and change had occurred in the history of life

  5. Conclusion

    1. Charles Darwin and many of his contemporaries had been taught to believe in the fixity of species
    2. The evidence, however, seemed to contradict this view
    3. Many naturalists began to think in terms of changing species over time––Darwin wrote to a friend that this was like “confessing a murder”
    4. Commonly, “transmutation” was considered the work of a mystical force
    5. Darwin, however, rejected metaphysical interpretations and looked instead for a physicalist explanation for change