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Time

Time Conceptualization

Joseph L. Glick, Jr.

Target age or ability group: High School General Biology (all levels).
Class time required: 20 minutes for individual work, 30 minutes for review and discussion.
Materials and equipment: Calculator, student worksheet.
Summary of activity: The following activity attempts to establish a new mode of reference for the student's conceptualization of time. To present hominid evolution in terms of millions of years and endosymbiosis of eukaryotes in billions of years carries little meaning to a person that has difficulty thinking abstractly. This activity is designed to provide an alternative, albeit more appropriate method of visualizing time in the context of the recombination of DNA in sexually reproducing organisms (i.e., generation).
Prior knowledge, concepts or vocabulary necessary to complete activity: This activity serves the student as an addendum to the evolution unit and as a review of genetics. Concepts that the students should have a basic understanding of include:

  • structure of DNA
  • dynamics of DNA
  • meiosis
  • taxonomy
  • evolution
Teacher instructions: It should be emphasized that this activity is focused on conceptualiza-tion and the historical data included herein is generally accepted. The length of generations has been arbitrarily set and the dates used are widely accepted in history texts. Periods of time regarding hominid evolution are taken from Minkoff, Evolutionary Biology, 1984. It is imperative to this activity that a review is conducted after the students complete their worksheets. Encourage the students to estimate when prompted. Failure to estimate will diminish the 'learning potential' of this activity.

Special consideration should also be given to students from adopted or single-parent households that may have difficulty with an-cestral lineages. This activity is intended to provide an alternative 'measuring stick' for time, and students should not be given a sense of exclusion if little is known of their heritage.

  • After the activity, the students will be able to:

    • visualize the relatively short period of recorded history.
    • conceptualize the vastness of time needed for notice-able change to occur in hominids.
    • gain a sense of kinsmanship of all people by the realization that all of us have common ancestral lineages.

      References:
      Minkoff, Eli. Evolutionary Biology. Addison-Wesley, 1984.


Lab No.DateName

Using Generations to Understand DeepTime

I. Evolution defined:

The following list of 'postulates' provides a fundamental definition of evolution. This covers information from DNA and protein synthesis through genetics and Darwinian thought.

  • DNA controls the structural and physiological make-up of all living things.
  • DNA is passed from generation to generation by processes of meiosis and fertilization.
  • The genetic template received by an offspring is a combination of the parent's DNA.
  • Changes in DNA also occur through random mutation: inversions, frame-shifts, deletions, translocations, etc.
  • Through recombination of DNA, variation exists.
  • All living things produce more offspring than can survive.
  • Individuals within a species vary.
  • The individuals best suited to survive in a given environment will sur-vive and may pass on the advantageous traits to their offspring.
  • Given sufficient amounts of time and influenced by the environment, changes occur.

II. Time:

Given sufficient amounts of time, physiological change may occur. Likewise, many definitions of evolution include the term 'gradual' in describing the 'change.' Considering the enormous geological and biological changes that have occurred in 4.6 billion years, it leaves us with the paradigm of time . In order to more easily accept the realism of evolution, try to answer the following questions the best that you can.

    1. How long is a long time?
    2. How long before the gradual change becomes noticeable change?

III. Years or Generations ????

Time, of course, is relative. What is a long time for one person may not be very long for the next. For hypothetical reasons, let us establish a human lifetime as being 'a long time.' And since DNA recombination (molecular change) occurs at fertilization/birth, let us go further and establish an estimate for a human generation.

LifetimeGeneration
HUMAN75 yrs.25 yrs.

IV. Activity:

A. Tracing Your Ancestors:

Provide one or two pieces of factual information about your ancestors.

1.Parents__________________________________________________

2.Grandparents_____________________________________________

3.Great-grandparents_______________________________________

4.Great-great grandparents_________________________________

Four generations only takes us back approximately 100-150 years. What do you suppose people were like 10 generations or 20 generations ago? Do you know what language your ancestors spoke?

How many years would that have been?

  • 10 generations = _______ yrs.

  • 20 generations = _______ yrs.

In fact, to provide a more historical perspective, approximate the number of generations (assuming a 25 year generation) since the following events:

1. Bubonic plague

(1350 A.D.)

gen______

2. Mayans designate the number zero

(250 A.D.)

gen______

3. Christ born

( 0 )

gen______

4. Earliest calendar and Sumerian math

(2500 B.C.)

gen______

B. Evolutionary Change in Hominids?

1. Neanderthals to today

Neanderthals were Homo sapiens that lived 100,000 years ago. They built stone shelters, fashioned tools, made clothing, cared for their families, etc. Despite the stockier size and smaller height (~ 5 ft. tall), they are classified as true humans. How many generations have passed from 100,000 years ago to modern day? Have the physiological differences been significant? Explain.

2. 'Lucy' to Homo sapiens

The earliest genus of hominids is called Australopithecus. Characteristics of australopithecans include bipedalism, approximate adult height of 4.5 feet, and a cranial ca-pacity less than one-third that of modern man. This appears to be very dissimilar from us today. Therefore, how many generations do you think are necessary to bring about this change?

Assuming that 'Lucy' dates 3.5 million years old and the generation length is reduced to 15 years, how many generations of recombining the DNA from the earliest hominids must have occurred to become Homo sapiens (100,000 years ago)?

					________________ generations

Please comment on your answer to #2. Does this surprise you?

V. Prokaryotes to Eukaryotes (just for fun)

The earliest prokaryotic cells have been found in micro fossils dating 3.5 billion years. The earliest eukaryotic cells date 1 billion years. Assuming that the generation length of a prokaryotic cell is 1 hour, how many reproductive cycles occurred to get to eukaryotic cells?

	________________________________________________ generations


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