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Population Problems

  1. History of Population Growth
    1. "Lag phase" up to about 1800
      • before energy subsidy (~2 million years ago) humans were very much in the same boat as other animals, population was determined very directly by habitat
        • adequate and continuous food supply
        • mild weather
        • starvation was probably a significant mortality factor
      • the utilization of energy (probably burning wood) and resources (stone tools and weapons) allowed a greater flexibility in food supply and living conditions
        • population grew to about 5 million during the Pleistocene (stone age)
        • there were oscillations in population connected to food supply
          • abundant food led to growth, food shortage to decrease
        • interestingly, archaeological studies of pre-Columbian Americans shows that these fluctuations may not have been simple cause and effect
          • ie, while famine will no doubt decrease population, there appeared to be some sort of regulation of the birth rate with more children being born during periods of prosperity and less during periods of shortage (this may been simply due to the effects of adequate or malnutrition on fertility)
        • the first resource crisis was the large scale destruction of game animals during the Pleistocene overkill
      • encouragingly, at that time, the shortage of resources led to innovation, specifically agriculture was invented about 10,000 years ago
        • with agriculture came towns (literally "civilization") and population grew, probably into the tens of millions
        • although farming and towns stabilized food supply, with towns came epidemics
          • disease became a significant mortality factor
          • bubonic plague in the middle-ages seemed to have reduced the number of people but otherwise not to have influenced population growth
            • insecticides do the same thing with insects
      • around the seventeenth century science and technology increased the sophistication of agriculture and manufacturing; in the 19th medicine and public health began to make inroads into infectious disease; the log phase (exponential growth) took off
        • in developed nations starvation and infectious disease are not currently significant mortality factors; under these conditions, death rate decreases (life expectancy increases), the population growth suddenly depends on birth rate (the doubling time approaches one generation)
        • mortality factors become related to population density per se: stress & substance-abuse (primarily tobacco and saturated fat) related illness and violence, and to technology: accidents
        • once again, the birth rate is influenced by social conditions, under industrial/urban conditions fewer children are needed as grow-your-own laborers and retirement insurance, and each child diverts more of a families time and resources; thus birth rate decreased in industrialized nations
        • in contrast, in the less developed nations, death rate may have decreased in recent years, but the birth rate is declining much less rapidly
          • there’s some form of vicious circle at work here: the rapid growth of population hinders economic development, which then cannot control population
  2. Human Demography-the study of human population characteristics
      • the "shape" of the population affects the rate of growth beyond the mere number
      • see the population profiles (demographic pyramids) on pp 152,154,155,156
    1. Doubling time
      • doubling time: N=log2/log(1+P/100)
      • N = 41 years for P = 1.7%
    2. Fertility rate
      • the number of children produced, for zero population growth in the long run, this must be 1.0 per person
      • since not all people have children (and only women bear them) the "replacement value" is calculated in terms of total fertility per female
      • the replacement value for the US is given by the book as 2.1 children per woman
    3. Life tables
      • a demographic tool
      • also called actuarial tables
      • the static table is based on the number of people dying at each age at a given time (hence the term static)(sample on pg. 381: note that life expectancy increases from age 0 to age 1, and that women live longer than men until they are over the age of 75)
      • a cohort table is derived by tracking the same group of individuals over their life span
        • more accurate, but by the time its compiled, it’s useless since the group to which the data applies is dead (as is the researcher who started compiling it!)
    4. Birth & death rates
      • just as you would expect, it is the proportion of births and deaths to live population
      • generally expressed like a batting average, in parts per thousand
      • see table on p 157
      • if birth rate is higher than death rate, population increases
          • RNI = CBR - CDR
          • RNI: "rate of natural increase"
          • CBR: "crude birth rate"
          • CDR: "crude death rate"
          • Total Growth = RNI + immigration - emigration
    5. Two important factors that affect the relationship between demographics and population in an area
      • dispersal: the young are likely to move, decreasing the population of their native land, and increasing the pop in their adopted land
        • social conditions in the native areas affect the rate of emigration
        • the rate of immigration has an affect on social conditions in the adopted areas
      • age distribution
        • this the demographic pyramid (pp 152, 154, 155, 156)
        • the slices in the 15 to 50 year old range are the ones creating the bottom slice; the 15 to 20 year old chunk is the one that accelerates or decelerates the birth rate
        • recently decreased death rate with continued high birth rate gives the broad, pointy pyramid characteristic of high population growth areas
        • more stable populations have more straight sided pyramids
        • the shape of the pyramid has other social effects
          • some say the pyramid will be top heavy when the boomers get to retirement age
            • the predicted median age is 60 in 2100
    6. The Demographic Transition (see pp 158-159)
      • as a society undergoes economic development, sanitation, medicine, agriculture, and so forth improve
        • the death rate drops
        • birth rate initially stays the same although infant mortality drops
      • the cost of having children increases as the economic benefit of children decreases
        • the birth rate decreases
        • population growth stabilizes with the population at a higher level
  3. Stress
    1. Environmental influences
      • the major causes of death can be related to chemical, social, and emotional stress
      • the crowding, noise, odor, and grime of cities is thought to be depressing
      • the lack of stable social structure (ie, loss of values or norms) is also thought to be disruptive to peoples mental equilibrium
      • rapid change in the social and physical milieu is also stressful
        • something as simple as the biannual daylight savings time shift has been shown to significantly increase accidents and mortality
    2. Physiological effects
      • some have attributed the high rates of cardiovascular disease to a lack of physiological outlets for fight-or-flight stress responses
      • certainly there are chemical insults in the environment (including self-inflicted chemical insults such as poor diet, cigarettes and other drugs) that contribute to heart disease and cancer
        • did anyone hear about the recent report that TSP is responsible for higher death rates in air polluted areas?
  4. Population Control
    1. Family planning vs pronatalist pressures
      • family planning is not a means of birth control, but rather a value or goal under which children are not born accidentally but rather as a result of conscious planning on the part of the parents
      • pronatalist pressures are all factors favoring an increase in the birth rate
        • children are "social security" in pre-industrial societies
        • many (most?) cultures prefer boy children, so couples have more children seeking a son
        • male ego
          • contraception is more effective when taught to women
      • in practice, without some social institutions favoring family planning, more children may be born than were desired
      • social and technological controls must be provided; also, local, regional or worldwide norms opposing family planning or birth control must be overcome
      • under Reagan/Bush, US financial support for family planning efforts in the developing nations was hampered, in spite of a petition from some 45 nations presented to the US congress in 1987
          • most (about 3/4) of the funding for family planning efforts come from the developing nations themselves
          • these nations recognize the potential hindrance to economic development posed by runaway population and the potential for conflict, overconsumption etc.; individual citizens of these nations recognize the burden of too many children
          • reaching the poor, young (under 20), far-flung people of these nations is a daunting task
      • what is needed:
        • counseling of single people and couples concerning the process of reproduction and birth control; education of women shows a clearcut inverse proportionality with fertility rate in developing nations
        • available means of contraception
        • pre- and postnatal health care and counseling for mothers, proper sanitation, nutrition, hygiene, to promote healthy children
        • promotion of the advantages of spacing children (eg through extended breastfeeding)
        • access to a safe abortion when a woman so desires
    2. Assuming mortality factors are constant, to achieve population control the birth rate must be controlled:
      • Abstinence
        • as the book points out, given the nature of the sex drive, it is probably not realistic to expect abstinence to be fully effective as the world’s means of population control
      • Contraception
        • chemical contraceptives for her
          • oral contraceptives
          • Norplant
        • chemical contraceptives for him
          • gossypol and others are still on the drawing board
        • barrier methods, in particular the condom, is having a public relations blitz due to its role in preventing STDs as well as pregnancy
          • similar barriers exist for her (ie the diaphragm) but recent work has focused on the so-called "female condom" I’m afraid that I must plead ignorance concerning the details
        • sterilization: the most popular form of birth control in the US, extremely effective and hassle free (after the initial surgery) but typically irreversible
    3. Abortion
      • a politically and emotionally sensitive issue
      • the removal or destruction of a fertilized ovum by surgical or other means
      • biologists remind us that one half to three fourths of all conceptions spontaneously abort--this works out to a spontaneous abortion rate of about 1300 to 2000 per 1000 live births; in comparison, the rate of induced abortion in the US is about 330 per 1000 live births
  5. The Future
    1. Why do we need population control?
      • in 1973, the Club of Rome published a paperback entitled The Limits to Growth
      • this book, based on a computer model of economic, biological, ecological, and resource factors, warned that humanity was headed for disaster if present trends continued
      • in such a scenario, increasing population serves as a feed forward control increasing the rate of resource depletion, pollution, habitat (and cropland) destruction and more population
      • as Malthus pointed out, an exponentially increasing population will outgrow its food supply
      • food supply is not the only factor, the computer simulations behind Limits point out that resource depletion and pollution are serious contenders for limiting factors on prosperity and population growth
      • every habitat is finite, and hence has a given carrying capacity
        • humanity’s habitat is not likely to be otherwise
        • ecology shows us that when birth rate pushes population beyond a systems carrying capacity, serious "mortality factors" prune the population and environmental destruction/depletion ensues
    2. food for thought
      • a famous religious leader has cautioned us to fight poverty not the poor; what do you think about that notion?
      • civilization has made it this far, what do you think lies ahead?

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