It is reasonable to assume
that the characteristics that define us are distributed across our
population like a bell
curve, which has a central bulge including about two-thirds of
the people with the characteristic, and two "tails" on
either side of the bulge that each include about one-sixth of them. A
typical characteristic is influenced equally
by our biology and experience, with each of its aspects (observable
values, such as the color of one's eyes) best suited to survival and
reproductive success in a particular type of environment. If the
environment changes, experience may compensate faster than biology,
which depends on generations of breeding under restricted conditions
to manifest significant changes. To a high degree, each of us shares
the same genetic makeup even though we manifest very specific aspects
(values of characteristics), which as a practical matter means that
over enough time and environments some of our descendants may have
aspects like people in other parts of the population.
The
greatest differences between people are between those at the extremes
(the ends of the bell curve's tails), but the actual number of people
involved is small: precisely one person for each extreme. At the
beginning of civilization, each of those two people was one-millionth
of the world's population. By 2013, each person was one of 7.1
billion people, the difference between them (the width of the bell
curve) was
one-third larger than at the beginning of civilization due to the
increase in population, and each of the original one-millionths of
the population had grown to the size of a town.
Each
characteristic imposes its own scale on this overall population curve
based on the range of possible aspects. That is, the width of the
curve is measured as the difference between the highest and lowest
values, and the center of the curve is the average of the two. The
units will be different for different characteristics, though they
all describe the same population. If the low or high value changes,
then the curve will appear to either change its width or its position
(sliding forward or backward), resulting in everyone changing –
again, relative to the particular characteristic. If the changes
allow for a larger population, then the population may grow; if the
changes restrict the population, it may decrease.
For
example, if consumption of a particular resource is the
characteristic, then greater access to that resource will increase
the maximum amount that can be consumed, widening the curve as long
as someone continues to consume the minimum amount. If the minimum
consumption is increased by people by distributing resources, the
curve may then shrink in width and appear to have moved as a whole
toward greater values, reflecting the fact that everyone is consuming
an equal amount more than before access was increased. If access to
the resource is reduced, however, and the minimum consumption is
reduced, the curve may slide backwards; and if there is some critical
minimum value of consumption below which people can't survive, the
result will include a reduction in population.
For
a critical characteristic – one whose changes affect population –
it makes sense that people would resist changes that could decrease
the population, or even be perceived to do so. Those who could
experience any reduction in population first would be most resistant;
but unfortunately, because they are likely to be on a tail of the
bell curve (such as those at the lowest level of consumption in the
example above) and have only a small number of people to help (people
like them), they would be the least able to prevent it unless they
could increase their own numbers to compensate.
The
least vulnerable people, at the end of the other tail, would
experience the narrowing of the curve associated with an increase in
the minimum value, without a corresponding increase in the average,
as a personal decrease similar to a sliding of the curve toward
population loss, and instinctively resist it for that reason. If
their resources were great enough to compensate for their lack of
numbers, they might even be somewhat successful at doing so.
Given
the inherent inertia in the bell curve's central bulge, it would be
tempting for people to attribute a change to those on the tail
associated with the direction of the change. For instance, increases
in the average would be attributed to those on the leading edge of
the curve, and decreases would be attributed to those on the trailing
edge. To actually make a change, though, the people in the bulge
would need to be convinced to actually make the change. During such a
change, the bell shape of the curve might not be preserved; there are
other curves that could describe the population until, in a more
stable state, it settles into its new yet familiar form.