A Slime Mold’s View Of Time

24 05 2010

Good tidings and well-wishes!

I’ve recently been reading John Tyler Bonner’s very intriguing, albeit imperfectly written (his writing style can, on occasion, be needlessly vague), book entitled “Why Size Matters: From Bacteria To Blue Whales” which, as the name suggests, analyzes the role of an organism’s size in it’s evolution, ecological niche, population density, and anatomy/physiology.  Dr. Bonner is perhaps best known for his expertise in the field of Slime Mold research, a fact which resulted in the following essay that first appeared in the Buddhist magazine Tricycle following a request from the magazine’s editorial staff just before the dawn of the 21st century. Although some of the prose contains a degree of anthropomorphism (which, given the non-scientific context, is excusable), I think that, overall, it nicely articulates just how ‘relative’ time often is in the scientific sense:

“Time From The Point Of View Of A Slime Mold”

Time and life are intertwined in so many different ways, something all biologists are acutely aware of. Consider a few extremes: a single cell bacterium may have its entire life cycle in half an hour, but a generation for an elephant takes 12 years and a giant sequoia 60 years. One reason I work with slime molds, which are soil amoebae that start off as single cells, and then come together to form a multicellular organism, is that their generations are short, so that if I start an experiment on Monday, I will know the result by Wednesday or Thursday. This kind of biological time–life cycle time–is at the middle of the time scale of living phenomena.

At the faster end of that scale is physiological time: how many beats does a heart have in a minute, or how long does it take to swerve the car in order to avoid a squirrel on the road. As with life cycles, these rapid living activities are greatly affected by size, so a huge elephant will have about 25 heartbeats per minute, while a tiny shrew’s heart goes at the amazing rate of over 600 beats every minute. The elephant will step to one side with slow deliberation compared with a small sparrow on the willow ledge with its lightning movements. We can combine the concept of the time required for a life cycle and the time required for rapid physiological processes in an interesting way. A shrew will live only a year or two, but an elephant will average 40 to 50 years; yet they have one thing in common: the total number of heartbeats they have in their whole lifetime will be approximately the same. So life for the small beast goes faster because its engine is racing along compared to the larger beast, and the total budgets for their actions are the same.

Evolutionary time is another time scale in the realm of life. Now we are no longer dealing with one generation, but with a great series of generations going way back in time to the beginning of life on earth. We are no longer dealing with minutes or a few scores of years, but with millions, and even billions of years. We find in the fossil record an era when all life consisted of cells, which later were followed by simple multicellular organisms, leading ultimately to all the great variety of animals and plants that we see on the earth today. This has been an exceedingly slow and exceedingly grand evolution that has taken up a vast quantity of time–so much so that it is difficult to comprehend the magnitude of geologic time. And we know that even these time spans are modest compared with those of the astronomer, who thinks in terms of light-years*.

So what does a biologist think of this second millennium? It is too short a time for major changes in evolution, but time enough for many generations. Every 1000 years will allow some 50 human generations, but the shrew will have a new generation each year, which means [some] 1000 each millennium. So for slime molds and shrews, the second millenium has meant waiting impatiently for a huge number of generations, while for elephants and ourselves–the wait barely tries our patience.

* [(I fully realize that a light-year is a unit of distance, and not time. However, the enormous amount of time required to travel between them preserves Bonner’s point.)]

The sheer magnitude of time with which paleontologists work on a daily basis is every bit as humbling and awe-inspiring as the vastness of space so eloquently celebrated by a host of passionate astronomers and astro-physicists throughout the ages from Issac Newton to Carl Sagan. 

But alas, I’ve said too much already! To those among my readers who study the field of long-vanished life, either professionally or as amateurs such as myself, I’d like to ask how this knowledge of deep time affects you outside the realm of scientific pursuits and during the course of day-to-day life.

May the fossil record continue to enchant us all!

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One response

31 05 2010
Moldtruth

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