PBIO 100 Lecture Notes

I. Plant systematics: see also summary of taxonomic methodology

• A. Common names
  • 1. Have evolved over centuries in a multitude of languages
    2. Sometimes only used in a limited geographic area
    3. The difficulty with common names - one plant may be known by several different names and the same name may apply to several different plants

  B. Scientific names [REQUIRED READING]

  • 1. Each unique kind of organism is known as a species; similar species form a group called a genus (plural - genera). Genera, in turn, are grouped into families, these into orders, classes and phyla.
    2. Each species has a single correct scientific name in Latin called a binomial (two names) that is always italicized or underlined.
    • a. the first name is the genus name; the second is the species epithet (specific epithet)
      b. example: the genus of maple trees (Acer) has many different species including "red maple" (Acer rubrum), "sugar maple" (Acer saccharum), and "black maple" (Acer nigrum)

    3. Taxonomic hierarchy

    • a. species that have many characteristics in common are grouped into a genus
      b. related genera that share combinations of traits are grouped into families
      c. related families are grouped into orders
      d. related orders are grouped into classes
      e. related classes are grouped into divisions or phyla
      f. related divisions are grouped into kingdoms.

    4. What is a species?

    • a. a set of individuals that are closely related by descent from a common ancestor and ordinarily can reproduce with each other but not with members of any other species
      b. other definitions

    5. History of classification [REQUIRED READING]

    • a. Theophrastus (370-285 BC) -- early Greek and student of Aristole
      b. Dioscorides (first century AD) -- Roman who wrote De Material Medica
      c. Herbalists -- Renaissance botanists who wrote herbals: book on the medicinal uses of plants

    6. Carl Linnaeus (1707-1778): Father of Systematic Botany [REQUIRED READING]

    • a. established modern system of nomenclature
      b. summarized world's flora in Species Plantarum in 1753

II. Evolution - change over time; Organic Evolution is genetic change in a population of organisms that over time

• A. Must be genetic-inherited, not acquired
  B. The concept of evolution originated long before Charles Darwin (1809-1882)
  • 1. Aristotle (384-332 BC.) - saw design and purpose in nature and thought living organisms moved from an imperfect, simple state to a more perfect, more complex state
    2. George Cuvier (1769-1832) - promoted the notion of "Catastrophism" as a result of his study of fossils. He argued that there were repeat creations and extinctions, the latter caused by floods or droughts. He published in 1825.
    3. Jean-Baptiste Lamarck (1744-1829) thought organisms were driven by some inner force toward greater complexity; thought organisms could pass on traits to their offspring that they acquired during their lives ("Lamarckanism"). Proposed his theory in 1809. Eramius Darwin (1731-1802), Charles's grandfather, promoted a version of Lamarckanism, using mainly animals to support his theory although his style of writing is often more admired than his views on evolution.
    4. James Hutton, a geologist, championed "Gradualism", a view supported by Charles Lyell, another geologist, and adopted by Darwin. They, like the zoologist George-Louis Buffon, were convinced that the earth was hundreds of thousands to million of years old; not some 6000 years as was maintained by some biblical scholars.
    5. Others, contemporaries of Darwin, also worked on the problem of evolution in the broad sense.

III. Darwin [REQUIRED READING]

• Historical Review [REQUIRED READING]
  
• Darwin's place in historical time
  A. Darwin could not accept the idea that living organisms are "specially created" or that they are unchanging, appearing today exactly as their ancestors have always appeared.
  B. Proposed that evolution occurs by natural selection
  • 1. 5 year trip as a ship's geologist/naturalist on the H.M.S. Beagle - spent time in South America and in Galapagos Islands
    2. He theorized that tortoises, finches, lizards, "sunflower" trees, and other unique plants and animals on the Islands were similar to forms on the mainland of South America because they were descended from those organisms.
    3. The differences between each island group resulted from the inhabitants of each island having been isolated from each other and changing slowly and separately in response to the conditions on their own island.

  C. Timing was right for Darwin's proposal

  • 1. Artificial selection- selecting and breeding only those individuals that possessed desirable traits
    • a. Bull dogs, St. Bernards, Chihuahuas, beagles- all same species
      b. Cabbage, cauliflower, broccoli, kale, kohlrabi, Brussels sprouts- all same species

    2. Thomas Malthus' work on populations

    • a. Populations tend to increase geometrically
      • 1 -> 2 -> 4 -> 8 -> 16 -> 32 -> 64 -> etc.

      b. Eventually, population size is checked by factors in the environment- lack of food, disease

    3. James Hutton (in 1795) and Charles Lyell (in 1831) argued the earth was far older than had previously been suspected. They argued for a gradual change over time ("Gradualism") for geological changes.

  D. Darwin's mechanism of evolution by natural selection, developed mainly from 1835-1844 and refined until 1858, was independently developed by Alfred Wallace (1823-1913), working in Malaysia and Indonesia in a matter of a few days while ill. He summarized Darwin's entire theory in a short letter sent to the Linnean Society of London in June of 1858.
  E. Darwin's work had been seen (as early as 1844) only by the botanist Joseph Dalton Hooker (1817-1911); Hooker and Lyell showed Wallace's letter to Darwin and urged a joint publication. This was presented as a joint paper to the Society on 1 July 1858 with publication of the paper following a few months later.
  F. Darwin abandoned his huge manuscript and decided to publish an "abstract". This appeared on 24 November 1859 with the title On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. The entire printing of 2500 copies was sold that day.
  G. The Origin caused considerable argument [REQUIRED READING] between scientists and philosophers, with both noting his theory's failures [REQUIRED READING].

  • 1. Supporters included Thomas Huxley, known as Darwin's bulldog; Joseph Dalton Hooker, a botanist at the Royal Botanic Garden, Kew, England; and Asa Gray, a Harvard University botanist, his American champion.
    2. Opponents included the English zoologist and head of the British Museum (Natural History) in London, Sir Richard Owens and Gray's Harvard fellow professor Louis Agassiz.

IV. Evolution by natural selection

• A. Darwin's [REQUIRED READING] observations about the natural world
  • 1. Variation- individuals vary and this variability is heritable
    2. Overproduction- each species produces more offspring than will survive to maturity
    3. Competition- organisms compete with one another for the limited resources available to them
    4. Natural selection works on the individual phenotype, and thus selects individuals which, in turn, change the population gene pool
    5. Survival to reproduce (survival of the fittest) - individuals that are selected must be able to produce viable, fertile offspring to pass on the successful genes within the population
    6. Time - long periods of time must be available, since some changes occur slowly

  B. As a result of natural selection, there is an increase of "favorable genes" and a decrease of "unfavorable genes" within a population
  C. Over time, enough changes may occur to cause a new species to arise

V. Rates of Evolution - Two interpretations about the pace of evolution based on the fossil record

• A. Traditional view- Gradualism- evolution proceeds as a slow and steady accumulation of changes in organisms (Darwinian)
  • 1. Not much evidence for this in the fossil record (one notable exception- Sheldon's work with trilobites in late 1980s)
    2. Interpretation- the fossil record is incomplete - not many fossil flowers or fungi, don't preserve well

  B. Many evolutionary biologists support- Punctuated equilibrium- evolution proceeds with periods of inactivity followed by periods of very rapid evolution (Gould & Eldridge model)

  • 1. Fossil record supports this more- long periods of stasis (no change in species) followed by rapid change
    2. However, fossil record is evidence of morphology (structure), while evolution encompasses morphology, ecology, biochemistry, and behavioral changes (that is, there may be stasis in morphology while there is active evolutionary change in the other areas)

VI. Modern Evolutionary Theory

• A. Darwin and Wallace had no concept of modern genetics
  B. Early genetics rejected the concept of natural selection
  C. Modern views of evolution formulated from 1938 until 1950 by numerous biologists
  D. Concept of punctuate equilibrium and related theories proposed from 1972 to present

Other sites of interest:
A solid summary
Historical summary
Summary of Natural Selection
A fair summary with animal examples
Outline of the history of systematic botany - More than you need!

Delwiche

Last revised: August 26, 1998  Straney