2.0        The Curve of Life

    The UN website lists a handful of researchers that have attempted to calculate the population of the Earth
    in the distant past. [1]  Regression analysis is a murky science when applied to demography, but this is all
    we have. If these experts are correct, there were anywhere from 1 to 10 million people on the planet at the
    start of civilization, 10,000 years B.C. Few demographer should feel uncomfortable with this estimate
    considering that it involves such a wide range. By the year 0, population seems to have climbed to 200
    million, in the year 1000 it was chugging along at 300 million, and 800 years later we finally reached a
    billion. Hence, it took humans 1800 years to grow arithmetically from two hundred million to 1 billion.
    Then, from 1800 onwards, the population seems to have exploded. We went from 1 billion to over 6 billion.
    Clearly, something happened that triggered the exponential growth of our species (Fig. 1).

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    Last modified 03/03/08


        Copyright © by Nila Gaede 2008
All species
eventually
conquer the
invisible bugs
that keep their
numbers back
Adapted for the Internet from:

Why God Doesn't Exist

    So what could have been responsible for such inordinate mortality? Were lions still pouncing upon us?

    The layman brainstorms the usual host of causes and agents that stopped us from expanding: predators,
    environmental changes, acts of God, starvation, war, and disease. What else could have checked our
    unmitigated advance?

    But then which of these factors was it that had the greatest impact?

    The demographers seem to have reached consensus on this issue: the number one agent holding our
    numbers back was disease, specifically mass diseases. Viruses and bacteria did what no army or
    earthquake or tsunami could. They attacked thousands of individuals simultaneously, unnoticed, and
    with lethal precision. Even in wars most people mostly die of disease and not in battle. Diseases
    relentlessly mowed humans down even in times of peace and specifically targeted the very young.

    Diamond [2] believes that the origin of mass diseases can be traced to the start of civilization                        
    (i.e., the agricultural phase). Domestication of plants and animals enabled Man to inherit the best of both
    worlds -- animals and plants -- and become the first ‘omnivore’ to rule the planet. The first 'pets' that we
    domesticated were the chickens, pigs, cows, horses, dogs, cats, lamas, camels, sheep, and goats.  
    Unfortunately, when these animals are confined in high densities, endemic viruses and bacteria have a
    field day and multiply. Some of these diseases mutate and find a better host in the masters themselves.
    The plague is an example of a crowd disease that did not get along with its host. It is believed by many
    that bubonic plague is responsible for wiping out from a third to a half of the population of Europe from
    1348 to 1352. No wars or natural accidents even remotely erased such high percentages of humans from
    the face of the Earth. The first crowd diseases to emerge were likely those that chose a physically easy
    mechanism for transmission: those that were airborne, those that were transferred to us by fleas, ticks,
    and mosquitoes, and those that swam in our drinks. They include some of the famed childhood diseases:
    smallpox, chicken pox, measles, mumps, whooping cough, and scarlet fever.

    Until the beginning of the 19th Century crowd diseases are said to have accounted for the deaths of as
    many as 50% of the children under the age of 5. [3]  [4] Children that survived still had to face a host of
    standbys throughout the rest of their lives, the likes of tuberculosis, typhus, typhoid fever, dengue, yellow
    fever, malaria, salmonella, anthrax, polio, bubonic plague, syphilis, and leprosy just to name a few. We
    tend to forget that our forefathers stared at death in the face much more often than we do. Hence, it did
    not matter that women had lots of babies throughout the agricultural epoch if few of these survived to an
    age where they could have children of their own.

    This situation changed dramatically at the beginning of the 19th Century with the introduction of vaccines
    and improvements in living conditions. Children that would have otherwise died now lived to reproduced
    children of their own, and adults who would have otherwise died early now fulfilled their natural life
    spans. Suddenly, the population, as well as the average age of the population, increased dramatically in
    what were fated to become the most advanced nations. Neither the young nor the old died, and the high
    pregnancy trend did not subside until after the middle of the 20th Century. Hence, for the thousand years
    leading up to the 19th Century we have two trends. One a flat curve marked by high birth and death rates
    and another marked by high birth, low death rates (Fig. 2). These numbers suggest that disease is the
    main agent that accounts for the two demographic trends just analyzed and that vaccines and better
    living conditions accelerated the conquest of our last natural enemies.

Fig. 1

Arithmetic and exponential demographic growth
Fig. 9.4   Arithmetic (b≈d) and exponential (b»d) demographic growth
    We should, however, be careful not to overestimate the muscle of artificial selection. The geometric
    expansion would have happened eventually even in the absence of vaccines. By the 19th Century, Man
    was already on the road to conquering these invisible enemies through natural means. For example,
    smallpox is regarded by many to be the greatest killer of all time. [5] This disease had apparently been
    around at least since the reign of Pharaoh Ramses V who is said to have died of its effects. [6] The bible
    mentions boils and blains (Exodus 9:8 - 9:11; Job 2:7), indicating that the ancients were familiar with such
    symptoms. It is also probable that Pericles died of a smallpox-like disease during the siege of Athens. [7]
    Some of these diseases may have mutated over time and caused different symptoms in those days. This
    may explain the disagreement among contemporary historiographers as to which disease affected a
    particular region in the past. What is indisputable is that, by the 15th Century, Eurasians had settled into
    an uneasy truce with smallpox whereas the native populations of the Americas had yet to experience their
    first case. [8] The reason for this disparity is that the Americas lacked cattle, the likely source of smallpox.
    Thus, the naturally immunized conquistadors of the 15th Century watched in amazement as the ‘Indians’
    succumbed to the divine, invisible agent that discriminated between the holy and the heathen. [9] [10]
    This experiment would be repeated over and over in the colonization of several Pacific Islands. [11]
    Therefore, humans were already acquiring natural immunity to smallpox and other diseases before the
    discovery of vaccines, and we can safely conjecture that, had we conquered the microbes through
    natural selection, the population would have later expanded exponentially anyways. Exponential growth
    was simply unavoidable. It was in the cards the moment Mother Nature was pregnant with Man.

    There are three lessons to be gleaned from these facts:

    •        Man’s conquest of disease was inevitable.

    •        Therefore, our exponential demographic phase was in retrospect predictable and inevitable.

    •        Plants and animals also adapt to diseases and enter an exponential demographic phase.

    Skeptics may have trouble with my last conclusion, so I’ll pitch in a little bit of evidence. It is well
    established that animals have developed immunities to diseases that devastate humans and other
    animals. Snakes are practically immune to salmonella, [12] macaque monkeys are largely unaffected by
    Herpes B Virus, [13] and fleas and rats have reached an agreement with the bubonic plague. [14] Plants
    are plagued with all types of diseases, [15] yet they manage to develop natural resistances. [16] [17] This
    suggests a lengthy period of adaptation between host and guest. What I am getting at is that Dimetrodon,
    T-Rex, and Neanderthal were no different. Exposure to transmittable diseases would have eventually
    resulted in increased resistance. Immunity or partial immunity would have given these species the ability
    to increase faster. Some dinosaur and Neanderthal bones exhibit signs of arthritis, an ailment of old age,
    indicating that individuals were attaining their natural life spans. Some analysts calculate that in order to
    grow so large, the sauropods had to have lived nearly 100 years. These facts imply that the species as a
    whole had apparently managed to build up its immunities.

    The epidemiologists may argue that new diseases or mutated strains irremediably fill the vacuum:

    “ Pathogens are evolving ways to combat our control methods…We’re going to have
      to run as fast as we can to stay in the same place.” [18]

    “ In the 1970s, eminent people were saying it was the end of the infectious disease era.
      We now find after the experience of the 1980s and 1990s, we are sadder and wiser.” [19]

    “ Influenza, which killed 20 million people in the year after the end of the first world war,
      is still a killer and has the capacity to change rapidly and spread widely throughout
      the world. Two attributes of the influenza virus – its potential for rapid genetic change
      and its ease of transmission – make it a continued threat that is often overlooked and
      underestimated.” [20]

    Therefore, if you’re wondering why we still have polio or the flu, or why there are different strains of AIDS,
    the epidemiologist has a ready answer. We are forever struggling with diseases and have no guarantees
    that tomorrow we won’t be decimated by a post-virus bug.

    The conclusions of these experts are myths as far as demography is concerned. In developed nations
    people no longer die of smallpox or malaria. They die of poor circulation, cancer, and other ‘diseases’ of
    old age. But even assuming that contagious diseases were to make a comeback, once the main strains
    have been neutralized and population is in the exponential phase, new diseases and mutated strains
    affect only a tiny fraction of the population. Most of the severe infectious disease cases are in Africa, and
    even there they have no chance of causing a dent in population. Referring to Sub-Saharan Africa,
    Bongaarts concludes:

    “ the AIDS epidemic is not expected to eliminate population growth.” [21]

    According to the U.N., despite that millions will die of AIDS in Africa, the nine most affected nations will
    almost double in size by the year 2050. [22]  Similarly, flu [23] and polio [24] viruses are known to have
    mutated. Should you be worried? Of course not! Today they claim a negligible portion of the world
    population:

    " Four million people have healthcare infections every year in the EU. Out of that
      figure, 35,000 die... We consider antimicrobial resistance or AMR as one of the
      major challenges for public health." [25]

    You have as much chance of catching a virulent disease such as mutated polio as you have of winning
    the lottery. [26] For all practical purposes, contagious diseases are a thing of the past. They are the least
    likely candidates to wipe out humanity in the future. Diseases are a problem only for epidemiologists
    tasked with minimizing the impact of epidemics and of new strains.

    To summarize, whereas in the past, it was the microscopic bugs that held our numbers in check, once we
    discovered them with our microscope, we slaughtered the last natural enemies we had on the planet. We
    would have eventually conquered them anyways through natural selection. Instead, we attained this goal
    much quicker using our intelligence and skills. This is a quantitative issue of time and not a qualitative
    issue of ‘whether’. Today, we are home free. Any new bug that arises has at most the potential to take out
    a small fraction of the population before we annihilate it under the microscope. Even in smallpox’s
    heyday, it had no chance of wiping out the entire population of Earth. We have for all practical purposes
    defeated the last enemy that all species eventually overcome. The conquest of disease indicates a long
    acclimatization process with viruses and bacteria. Therefore, it necessarily occurs towards the end of a
    species’ life cycle.

    But then, if we eliminated disease, which is what kept our numbers in check, why did the population of
    humans stop growing exponentially? Why is the population of our species growing at a slower rate?

Fig. 2
This graph more or less depicts
the 2000-year demographic
history of Man. We grew more
orless arithmetically until we
reached the 1-billion mark
around 1820. Afterwards Man
entered an exponential regime.
Consensus is that during most of
the agricultural phase (i.e., the last
10,000 years) women had a high fertility rate. In spite of this, the population did not increase
exponentially. The demographers believe that our high birth rates were offset by high
mortality.
At time T1 population P1 was
characterized by a regime in which
deaths balance out births.
Population increases very slowly.
The period of exponential growth
T2, in contrast, is distinguished by
a dramatic drop in deaths.
Exponential growth occurs when children that would have otherwise died
before reaching puberty now reach maturity and produce children of their
own. Compounding this growth is a non-trivial arithmetic component: an
increase in the average life span of a human. Both factors are health-related
(i.e., improved living conditions and eradication of contagious diseases.)