Life Span

Life span is a term often used in the science and medical fields, and I recently read that that can mean two different things.  The definition of life span in a medical dictionary is “the average or maximum length of time an organism is expected to survive.” Note there are two things to consider. Average life span is a statistical estimation of how long let’s say an animal is expected to make it against all the trials of life: disease, food shortages, being someone’s lunch, etc.  Maximum life span is a measure of how long an animal can live if everything goes its way, plenty of food, no predators, no disease or really bad winters, etc.


Several things come into mind when looking at the maximum life span of animals.  A house mouse has a maximum life span of 4 years, while the larger cat has a max of 38 years, and an elephant can make it to 86. So there seems to be a correlation (with exceptions of course) between longevity and body size… the bigs live longer. This may have something to do with lifestyle.  Smaller animals tend to live in the fast lane and perhaps burn our sooner. The average heart rate for a house mouse in over 500 beats per minute, a cat averages 140 per minute, while the elephant only averages 30.  All you Type A/multi-taskers out there (of whom I am one) might want to take note that a frenzied life may not lead to a long one.  Turtles, those easy going/take your time animals, live a long time.  The box turtles in our woods can make it 100 years, and the big Galapagos turtles can make 200.  Something to think about.


Humans seem to be an exception to the rule, living way longer than our size or heart rate would indicate.  Our average life span has moved up over the decades due to better food and medicine availability.  In the U.S. the average life span was on 39 year in 1850, by 1900 is was up to 48, then 56 in 1920, 61 in 1930, 67 in 1960, and now the average life span stands at 78.  Unfortunately not all humans of the world do as well due to poverty and harsh living conditions.  The average life span of a man in Swaziland is only 40 years.  Some think we have gone about as far as we can in raising average life expectancy through science and medicine, so 70 to 80 may be it. Three thousand years ago Psalms 90:10 stated that “Seventy years are given to us! Some even live to eighty. But even the best years are filled with pain and trouble; soon they disappear, and we fly away”.  How about that?  The present record for human longevity is 122, held by a French woman named Jeanne Calment.


Isaac Asimov wrote an article some years ago comparing life span with the number of times an animal’s heart beat.  He took the average heart rate of each animal and multiplied it by its maximum life span.  He did a bunch of mammals both large and small, and concluded that about a billion heart-beats is all you can hope for, and when those are done so are you.  But humans again turn out to be standouts. We hit our first billion heartbeats about the time we get our first real job (age 23).  By 75 we are approaching three billion beats.  Ms Calment’s heart cranked over four billion times in her 122 years.  So in the animal kingdom we are indeed blessed with long life, and one hard working heart.


This entry was posted in Nature. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s