Download Chapter 17 The Biological Impact of Agriculture and Civilization

Chapter 17
The Biological Impact of Agriculture and Civilization
Overview
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The evolution of the human species continues to the present day. Although biological change continues in human
populations, the rate of such change is most often exceeded by the rapid rate of culture change.
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Over the past 12,000 years, the human species has moved from hunting and gathering TO agriculture to feed itself,
and the total size of the human species has increased roughly a thousand-fold.
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These rapid cultural changes have influenced aspects of human biology by affecting our patterns of health,
physical growth, nutrition, mortality, and fertility, among other things.
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The subsequent rise of state-level societies with large urban populations was accompanied by further epidemics
and nutritional problems
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As people lived longer on average, the death rate due to noninfectious degenerative diseases increased.
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The recent changes in human history have occurred in the last 12,000 years
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One result is that biologically we remain hunter-gatherers.
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Another result is our population is now 7+ billion, estimated to reach 9+ billion before it levels off.
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Another is that we have more options for ‘making a living’
The Biological Impact of Agriculture 1
• The biological impact of agriculture
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The transition from hunting and gathering to agriculture was a major shift in human adaptation.
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The human population became more sedentary (settled in one place).
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The field of bioarchaeology provides data that shifting to agriculture could have negative effects on health
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Population growth
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The rate of natural increase is 1.2% per year. At this rate, the world’s population will double in 58 years.
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The more developed countries (MDCs) make up roughly 18% of the world’s population and have low birth
and death rates.
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The less developed countries (LDCs) make up 82% and have a natural increase of 1.5% per year.
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Their total population size is expected to increase by 47% by the year 2050
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Carrying capacity: The maximum size of human populations as supported by the relationship of population and
agriculture.
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It is small in hunting and gathering populations.
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Agriculture can support much larger populations.
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Two critical and interrelated questions regard the growth of the human species
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What will global population size be in the immediate future?
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How many people can the planet support?
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The questions are complex.
The Biological Impact of Agriculture 2
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Population growth (continued)
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Life expectancy at birth
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Is a measure of the average length of life for a newborn child based on a population’s life table (often called
an age-sex pyramid)
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In hunting and gathering populations, it is low (20-40 years)
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The shift to agriculture led to an increase in life expectancy.
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This was not true at Dickson Mound, Illinois (a prehistoric site) where HG had life expectancy of 26
years and agriculturalists only 19 years.
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The primary reason was they ate too much corn and did not diversify the diet.
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Population growth with agriculture is strongly linked to decreased breast-feeding and dietary changes that
improved ovarian function.
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Classic Demographic Transition model (more later in notes)
The Biological Impact of Agriculture 3
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Disease
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Disease in hunting-gathering populations
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The two most common types of infectious disease in hunting-gathering populations are due to parasites (lice
and pinworms) and zoonoses, diseases transmitted from other animals to humans (sleeping sickness, tetanus,
and schistosomiasis).
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Most diseases are endemic (occurring at relatively low, constant rates) in hunting-gathering populations.
Infectious disease in agricultural populations
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Larger population size in agricultural populations makes it possible for many to be susceptible to short-lived
microorganisms and epidemic (rapidly spread) diseases such as smallpox and measles.
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Sedentary life is the reason.
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Agricultural practices also cause ecological change making certain infectious diseases more likely.
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An endemic pattern shows a low but constant rate; hunting and gatherer populations do not have epidemics
for 2 reasons: Small population size & mobility
The Biological Impact of Civilization
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A civilization is a large, state-level society with characteristics such as large population, high population density,
urbanization, social stratification, food and labor surpluses, monumental architecture and a system of record keeping.
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Urbanization and disease
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Preindustrial cities increased in size and density, and provided opportunities of epidemics of infectious disease.
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Inadequate sewage and contamination of food led to the Black Death pandemic (widespread epidemic) in the
fourteenth century in Europe.
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Culture contact
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Expanding civilizations lead to an increase in long-distance contact with other societies, resulting in the spread of
infectious disease into populations with no prior immunity.
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Native Americans and Pacific Islanders were two populations affected by this.
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The flow of disease was primarily in one direction—the Old World to the New World.
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One disease that may have flowed from the New World is syphilis (but major source of debate).
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Watch The syphilis enigma
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In recent times, industrialization and economic development has resulted in major biological impacts on disease,
mortality, fertility, and population growth.
Changes in Modern Times 1
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The epidemiologic transition
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The epidemiologic transition is the increase in life expectancy and the shift from infectious to noninfectious
disease as the primary cause of death.
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This has been observed in the more developed countries (MDCs) and to some degree, the less developed countries
(LDCs).
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The nature of the epidemiological transition
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This transition follows initial high death rates due to epidemics of childhood infectious disease and later
improvements in public health, sanitation, and medical technologies.
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One particular aspect of the ET is the increase in life expectancy at birth.
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Between 1900-2009 the overall life expectancy increased from 47.3 years to 78.2 years
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Women live longer in MDCs; in 2009 life expectancy for males was 75.7 years and females was 80.6
years.
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Remember life expectancy at birth is different from your life expectancy now (you did not die) so “the longer
you live the longer you live”.
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While the global life expectancy has risen, it is uneven.
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In many countries women have a lower life expectancy than men.
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The primary change in life expectancy has been the decrease in deaths due to infectious diseases.
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In the US (1900) top 3 causes of death: pneumonia/influenza, TB and diarrheal diseases.
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In the US (2009) top 3 causes of death: heart disease, cancer, and chronic lower respiratory diseases.
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Causes of ET: Biomedical, health care, public sanitation and most of all clean water/s
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Case Study of ET: New York City experienced the epidemiological transition from the mid-1860s through the
1920s.
Changes in Modern Times 2
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Secular changes in human growth
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Secular changes are changes in patterns of growth across generations.
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Three basic types of secular changes have been observed in the past century
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An increase in height (not at birth, but later)
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An increase in weight (mostly during adolescence)
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A decrease in the age of sexual maturation, especially age of menarche
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Causes of secular change reflect environmental change, and were too rapid and pervasive to be genetic.
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Some possibilities include: improved nutrition, reduction in childhood infectious disease, improved available
health care, improved standard of living, and reduction of family size.
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Many of these factors are interrelated.
The reemergence of infectious disease
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Emergent infectious diseases
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New infectious diseases are emerging and the old ones are coming back in new forms.
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The Ebola outbreak; Legionnaire's disease; E. coli; HIV
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The emergence of new diseases shows the evolution of microorganisms.
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This is exacerbated by new technologies and environmental change brought about by human populations.
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Reemergent infectious disease
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Reemergent infectious diseases are infectious diseases that have evolved resistance to antibiotics
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Tuberculosis is an example
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Antibiotic resistance illustrates the principle of natural selection applied to disease-causing organisms caused
by a mutant form of bacteria.
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This is linked to indiscriminate use of antibiotics for treating illness in humans and in animal feed.
Changes in Modern Times 3
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Demographic change
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Demographic Transition Theory
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A model of demographic change that states that as a population becomes economically developed; a reduction
in death rates (leading to population growth) will take place.
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Will be followed by a reduction in birth rates.
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Describes the experience seen in some of the more developed countries today.
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There is considerable variation in the timing.
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There are also cases of the basic trends reversing.
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The United States in the twentieth century is an example when fertility rates first declined, then rapidly
increased following World War II.
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Implications of changing age structure
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A major effect of the demographic transition is on the age structure of the population.
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The age-sex structure (number of males and females in different age groups of a population) is a way of
examining population change.
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A population pyramid is a graphic representation.
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These look different when comparing LDC’s and MDC’s.
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Population pyramids in LDC’s show a high segment of infants and young children and high fertility
rates.
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MDC pyramids show fewer births, an increasingly higher median age and low fertility rates and an
aging population.
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Culture changes can be expected.
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Awareness of the problems and solutions is a step in the right direction.
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Successful integration of demographic change requires awareness.
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