relativity time biology age

The relativity of age

Time flies – but certainly not at the same speed for everyone

When Albert Einstein developed his “Theory of Relativity”, velocity played an essential role. If two trains, both speeding along at 100 km/h with regard to a stationary person on the ground, run side by side on parallel tracks, then -relative to one another- they do not move at all. If one of the trains is pulling ahead and increases its speed to 150 km/h, it is then travelling at a speed of 50 km/h relative the other, but for passengers in the faster train it looks as if the slower train has been moving backwards.

Turning to animals, the speeds with which the various species ‘race through life’ differ considerably and the ways how animals of different species manage to have some individuals reach their maximum life spans are also not identical. Take, for instance, humans and the freshwater pearl mussel Margaritifera margaritifera. Both are known to have a maximum life span of approximately 100 years. But when we plot the number of individuals of a given cohort (i.e. all individuals born in one year), which survive from year to year, then we see a tremendous difference between the two species. The so-called survivorship curve shows for humans, right up to an age of 70 or so, that relatively few individuals die early in life. However, at greater age the curve drops steeply to end at 100. The survivorship curve for the freshwater pearl mussel has a completely different shape: right from the start at year 1, there is an immediate huge mortality that lets the curve plunge steeply and shows that few individuals survive the first few years. But then as the surviving few individuals become older, the curve flattens and eventually ends where that for the humans ends, namely at age 100. Further beyond no individual (whether human or mussel) in this model example is expected to survive.

Of course, not all animals can live a hundred years. Amongst the mammals, marsupial mice of the genus Antechinus rarely even reach two years of age, dogs are very old at 15 years of age, elephants may attain 70, humans 100, and bowhead whales (Balaena mysticetus) 150-200 (based on the ages of harpoon heads found deeply embedded in the skins of recently killed whales). Scaling all these life spans to that of the human being’s 100 and looking at the relative speeds with which the various species race through life from birth to death, it follows that one year in a dog’s life, for example, is equivalent to seven years of a human being’s life. For the marsupial mouse Antechinus it would even be 50 years.

Could this explain why dogs become so desperate when left in a car or tied up outside a shop for an hour, while its owner has gone buying a few things (not necessarily dogfood, though!). If a one hour wait in a dog’s life means that this is equivalent to 7 hours of waiting for a human, wouldn’t we get impatient sitting in a car or being tied up outside a shop for that amount of time? And, of course, like the dog, wouldn’t we be extremely happy when this long wait is over and the person we love finally returns? I know, I would. Thus, if impatience is related to a ‘concept of time slipping by’, would animals possess such a concept at all? These almost philosophical questions have only partially been answered when it comes to animals and I’m now left wondering whether in the Sino-Japanese zodiac calendar of 12 animals, I would find the Year of the Monkey (i.e., 2016, 2004, 1992, 1980) to be longer or shorter than the Year of the Goat before or the Year of the Chicken that always follows a monkey year?

relativity time biology age

© Dr V.B. Meyer-Rochow and, 2015.
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