In the late
1960s, US scientist John B Calhoun created a ‘Mouse Utopia’ – an artificial
environment which provided what he regarded as the perfect breeding conditions.
To everyone’s amazement, and without any signs of disease or hardship; after a
few months of rapid population growth, the mouse colony ceased to reproduce at
all; and soon became extinct – every single mouse dying within three years.
Could Mouse
Utopia have lessons for humans? Well, that depends on the explanation for
extinction – but if Michael A Woodley’s hypothesis that the mice died of
‘mutational meltdown’ is correct, then humanity’s days could be numbered.
Woodley’s
hypothesis, which seems to be the only one to fit the facts (unlike Calhoun’s
own explanation of ‘overcrowding’), is that it was exactly the utopian
perfection of conditions which killed all the mice.
The idea is
that mice depend upon a very high death rate (mostly from predation) to
filter-out new and harmful genetic mutations which spontaneously arise each
generation. When nearly all of each mouse generation survives and breeds, then
the harmful mutations rapidly build-up to produce genetically unfit mice who
lack desire to breed, and who neglect their young.
Exactly the
same explanation could apply to Western humans since the industrial revolution;
because the average premature death rate, both pre-natally and in childhood,
has declined from about two-thirds to only one percent. If we assume that most
of the uterine and childhood deaths occurred among those least-fit children
with the most mutational damage – this must mean that Western Man has
accumulated something like eight generations worth of damaged genes.
The irony is that probably greatest triumph of the industrial revolution - the saving of so many lives of children - was perhaps therefore also the cause of a future 'Mouse Utopia' scenario...
But how bad
are human mutations? Geneticist Michael Lynch estimates that there may be dozens
of slightly-harmful mutations per human generation, among which approximately
one to three mutations will be significantly harmful. So, lacking the harsh and
cruel filter of high child mortality rates, each modern human generation would
be expected to accumulate a couple of extra harmful genes.
What effect
might these accumulating mutations have? Well, in a word they will reduce
‘fitness’ – Lynch suggests each harmful mutation might reduce reproduction by
one percent - which means they will in multiple ways reduce reproductive
potential for a given environment (multiple ways according to the chance of
which gene is mutated).
So, it seems
that the average modern human surely must be less genetically fit than his ancestor
of two hundred years ago. Then, why isn’t this more obvious?
One reason
may be that the most sensitive measure of reduced fitness is psychological,
rather than physical. We are therefore first likely to see
biologically-damaging changes in social, sexual and offspring-rearing behaviours;
before we see any clear increased rate of diseases (although an increased rate
in genetic disease would eventually be observable).
However, on
the other side of the coin; reduced fitness would only be directly measurable
if the environment had stayed exactly the same as in 1800; whereas we know that
the modern environment is much less harsh. There is less starvation and less
infectious disease; there have been breakthroughs in medicine and surgery, the
expansion of the welfare state – and so on. It seems likely that a softer and
more comfortable modern environment is mostly concealing a decline in modern
fitness – and life expectancy has been rising for many decades.
But
declining fitness is evident in the most fundamental biological measure – which
is reproduction. It was declining reproduction that caused the extinction of
Mouse Utopia; and the same pattern can be seen in the prosperous developed
nations today.
For example,
the age-adjusted native population size has been declining in Britain for
several decades, since deaths exceeded births in the 1980s. The average number
of children per women is now much less than two, especially among the
wealthiest and most highly educated (ie. those best able to care for children).
Median average age (excluding recent migrants) is probably into the late
forties, which means that a large majority of native Brits are beyond
reproductive age.
In brief,
the British population is headed for extinction – and for psychological rather
than physical reasons; and the same applies across all developed nations.
Woodley’s ‘mutational meltdown’ scenario would be expected to kick-in as
population decline combines with mutation-cased fitness decline to make a
down-spiral of ever fewer, ever more damaged people.
What are the
prospects? In a way the human situation may be worse-off than Calhoun’s mice;
because we are in the position of having to maintain our own ‘utopia’. But mutation accumulation will progressively
erode our ability to sustain a modern civilisation – as average health,
adaptiveness and abilities decline with each generation. Sooner or later, the
older mutated population will become unsupportable by the even-more-mutated
younger generation.
On the
positive side, it seems likely that something important is missing from the
simplified biological model underlying the above calculations; and there are
positive, cohesive forces at work which may tend to compensate for mutation
accumulation. I personally believe that there are as-yet undiscovered factors
which tend to work in opposition to the degenerating effects of natural
selection.
The question
is whether any such positive factors will be strong enough and rapid enough to
let us escape from the collapse of ‘Mouse Utopia’ which otherwise seems
inevitable.
