Nature 2019 February

It’s about time!

At the event we know as the Big Bang, some 13.88 billion years ago, there was no component or dimension which today we understand as time. Physicists define this as time zero. This is not to say this big bang moment is of no ‘duration’ or time was standing still, just that this period cannot be defined in terms of measured time.

Just over a hundred years ago, a period which already falls outside the memory of anyone still alive, even if it is but a mere moot in the eye for the universe, Albert Einstein developed his General Theory of Relativity. This theory proposes that time is not constant throughout the Universe. In the simplest of terms Einstein determined that the impact gravitational forces will affect the time duration measured by two observers at different locations and travelling at different speeds.

For all of us there are occasions when time passes in a jiffy and others when time seems to stand still. To a young child, be it on a car journey or stuck indoors on a rainy day time appears to take an age to pass. This is because time durations appear relatively long compared to their short lifetime’s experience to date. In contrast, these same periods experienced by a much older person seem to pass far too swiftly sometimes as the period is comparatively short relative to their much longer lifetime.

Is this just a human characteristic, made ever more noticeable by the prevalence of clocks? Could animals be influenced by observable landmarks in time? Consider how time might be perceived differently by short-lived and long-lived mammals. There are some rules of thumb for mammals whereby there are correlations between the mammal’s size and lifespan. The longest life spans tend to be found in the larger mammals and vice versa.

For example, at 1.8 grams the Etruscan shrew is the smallest terrestrial mammal in the world, and might only live for up to 6 months. meanwhile, one of the largest mammals, a Bowhead whale, weighs in at 100 tonnes, and can live to over 200 years. Shrews need to eat up to 200% of their body weight per day to support one of the highest metabolic rates in the animal kingdom. At the other end of the range the whale, which is some 50 million times heavier than the shrew, consumes around 2 tonnes of zooplankton per day, just 2% of body weight.

To transport gases, food and waste products around the body requires a powerful heart pump. The shrew’s heart beats 750 times per minute. With a much more efficient physiology, the whale’s heart needs only to tick over at a mere 8-10 beats per minute. To survive, very small mammals have a real struggle to consume sufficient energy-rich food to stay alive. For shrews every minute is precious as they forage for food, typically invertebrates found in the leaf litter. The whale can go without feeding for months before a visit to the rich feeding grounds in regions of the Arctic.

The contrast in the pace of life over such divergent life spans must have an impact on how such animals view the world. Does the shrew, scurrying around at breakneck speed, day in and day out for all its life, view the world around it in some kind of ultra slow-motion? Does the whale, cruisingaround leisurely throughout its lifetime view life in the oceans rushing by endlessly?

It might be reasonable to conclude that, for instance, an Orangutan is continually contemplating its surroundings, observing repeated events or learning from others in its troupe the implications for avoiding danger brought about by daily and longer-term changes in climate. It is well-known that the Orangutan has a complete map of the forest it inhabits. It not only knows where to locate each of over 500 species of food-plant but, crucially, when they can be found bearing new growth or producing fruit.

Such events, which would be unobserved by us unless we were indigenous people living also in the forest, must provide some concept that periods of time are passing by and there is a memory of previous periodic occurrences.

Compared to our animal cousins, be they our more distant relatives the pigmy shrews, or our much closer kin, the Orangutans, with whom we share, according to some analysis, some 97% of our DNA, we may or may not have a more sophisticated and longstanding grasp of The fourth dimension – time. We might think this to be the case but human nature has an overriding tendency to identify repeating patterns and individual events in the natural world which reassure us that the world around us is ticking along nicely. It could be our pet robin that we can set our clocks by when it visits the bird feeder around the same time each day over several years. In truth the bird has not retained a memory of visiting the feeder yesterday and given the annual attrition of robins it’s likely it was not the same robin as last year.

But, despite shattering some illusions, it is still reassuring to see the robin as usual as it is with so many other fixed and variable of nature’s events by which we fix the time or season. Like looking for when the first snowdrop of winter appears. Knowing when it is the best time to visit our favourite bluebell wood. Seeing the first swallow of spring and last of summer. Listening out for the cuckoo and remarking if it’s early or late this year. Harvesting fruit from the hedgerow in late summer. Remarking on whether the trees are turning brown earlier or later this year. Seeing the holly with red berries. Just a few of so many that we still know about or of the even greater number we sadly no longer record, that country folk relied on, were reassured by and celebrated.

It is About Time perhaps that we spent more of our valuable time observing nature’s clocks even though it often keeps a very different time to the one our precision time-pieces keep.