Message Number: YG5931 | New FHL Archives Search
From: RRC
Date: 2001-07-30 04:04:00 UTC
Subject: Re: Ferret/Human age ratios

Patti B. wrote:

<In this digest someone wrote that 2 years of ferret life is like
<20 human is that true that for every one year they are 10 of a
<humans. Patti B. Mom of Max and Bandit

Taking the average age at death of Americans to be roughly 75 years, and
the average age of ferrets to be roughly 7.5 years, then the ratio of 10
human years per ferret year would be about right. The problem is that
the initial part of the ferret ageing curve is different than that of a
human, so the first few years of a ferret's life can be quite different
than 10 times human years. For example, at the end of the first year of
a ferret's life, they are full grown, capable of reproduction, and
living independently. This places them at about 20 years when compared
to a human. Like in humans, during the middle years there are little
changes in the ferret's attitudes or behavior. This starts to change at
about 4 or 5 years, when ferrets begin to play less and sleep more.
Gradually, ferrets will begin to slow down, will lose their position of
dominance, lose most of their interest in play, and sleep for long
periods of time. This relates to humans at about 60-70. By 8 years of
age, many ferrets show obvious signs of old age, including changes in
bowel habits, lack of tolerance for food changes, and a lack of self
care. Some even seem forgetful, especially of the toilet location. This
roughly corresponds to about the 80s in humans.

While the beginning of the 10:1 scale is wrong, I do think that a five
year old ferret roughly corresponds to a 50 year old human, a six year
old ferret to a 60 year old human, etc. In other words, after five
years, I think 10 human years are roughly about the same as a year in
ferrets. Here is a rough scale *I* use (based upon established human
ageing parameters, compared to similar applicable signs of ageing in ferrets):


There are three important things to consider. First, my scale is based
on published signs of ageing and NOT upon experimental data. In other
words, it is possibleĀ—perhaps probableĀ—that a controlled study may find
my scale inaccurate. Second, all studies depend upon statistical
generalizations and do not necessarily apply to specific instances. In
other words, remember that ferrets are just like humans in terms of
ageing in that not all members of a species age at the same rate. Simply
put, not all 50 year old humans look or act 50; most seem about 50, some
seem older and some seem younger. This is normal, and ferrets are no
different. Third, and most important, while the national average age of
death for male humans is about 77 years, deaths around that mean are not
normally distributed. Rather, they are heavily skewed, with a slow, long
rise, a moderate plateau around the mean, then a rapid fall. This type
of distribution has relatively few deaths prior to the "national
average", with a lot of deaths after the mean. For example, in a normal
distribution, for every death at 50, you would have one at 104 (assuming
a mean of 77). However, in an aging demographic, for every death at 50,
you will have about 27 dying at 78 to maintain the average. In terms of
ferrets, that means relatively few die before 7.5, but at lot die after
that age, which is why ferrets older than 9 are very rare (and why
humans reaching the century mark are likewise so unusual).

Species have evolved to die after a few breeding seasons and when their
offspring are self-sufficient. This does two things. First, it maximizes
resources for the offspring, insuring their survival. Can you imagine
the success rate of offspring attempting to enter a landscape dominated
by older adults who have learned where all the good stuff was hidden?
The youngsters wouldn't have a chance! Second, when natural selection
weeds out the less-fit individuals, the resulting population is well
adapted to the environment. If the population was skewed to older
individuals and the environment changes, then the entire population
could die and the species becomes extinct. However, if the population is
dominated by younger individuals, prior to when natural selection can
weed out the less-fit, then there will be some individuals that can
adapt to environmental changes, and pass those traits on to their
offspring, thus insuring species survival. From an evolutionary
standpoint, limiting the time an individual can live might be really bad
for the individual, but it is really great for the species.

Bob C