Tuesday, 6 December 2016

Edward Forbes and testable hypotheses

Although he was only 39 when he died, Edward Forbes had a lasting influence in Botany, Zoology and Geology, from both his published work, his lectures and his enthusiasm in supporting others. He had many friends and it is not possible to read the memoir by Wilson and Geikie [1] without feeling the affection in which he was held by fellow Natural Historians. As Daniel Merriman wrote, he must have been "a gentle lovely man"[2] as well as an eminent Professor.

In the field of Marine Biology, Forbes was a strong proponent of the use of dredges to scrape over the sea bed – an example of a dredge is shown above from the NOAA website (in an article that contains a typical poem by Forbes) [3]. He recognised the zonation of organisms on shores and identified the following zones after dredging studies of the Aegean Sea, each being characterised by different groups [1]:

He found that the [Aegean] could be sub-divided into eight provinces of depth; first, as around his own native islands, came the littoral zone, which, from the feebleness of the tides in those seas, did not exceed a range of two fathoms. The second region reached from 2 to 10, the third from 10 to 20 fathoms below the sea-level. The fourth region ranged down to 35 fathoms, the fifth from 35 to 55, the sixth from 55 to 80, and the seventh from 80 to 105. Each of these zones showed a marked and peculiar assemblage of living beings, and could even be further separated into sub-regions. The eighth region included all the space explored below 105 fathoms, and embraced a depth of 750 feet. It was an unknown tract – a new sea-country now added by Edward Forbes to the domain of the naturalist. In the lower zones, the number of species gradually diminished as the dredge sank towards the abysses. From 230 fathoms below the sea-level – the greatest depth Forbes reached – he drew up yellow mud with the remains of pteropods and minute foraminifera, and occasionally a shell. From a comparison of his observations, he conjectured that the zero of animal life would probably be found somewhere about 300 fathoms.

In their paper reviewing this azoic hypothesis [4], Anderson and Rice point out that there were several records of animals being taken from deeper water, even before Forbes dredged the Aegean. They conclude their paper with a section on the benefits of false hypotheses:

The controversy surrounding the azoic hypothesis was not so much due to problems with the theory itself, but rather the reluctance of many contemporary scientists to accept contradictory evidence. By proposing it, Forbes paved the way for later discoveries by stimulating the debate among leading naturalists of the day about how the marine environment influences the distributions of the plants and animals that live in it. For theories, including erroneous ones, are absolutely necessary for the advancement of science.

The acceptance of the azoic hypothesis reflected, in part the status of Forbes in the world of Natural History in the nineteenth century. However, his hypothesis was testable by further investigation and we now know that there is a fascinating, and sometimes abundant, fauna in the very deep regions of oceans.

Some scientific ideas are tricky, or even impossible, to test and those that involve very long time scales are typical of these. For example, conditions in hydrothermal vents provide physico-chemical conditions that promote the formation of the essential organic precursors of the first living organisms. Although we have only known about these vents for less than half a century, it is now possible to hear scientists give talks assuming that life on Earth began in hydrothermal vents, as though repetition of this "fact" establishes its truth. I'm convinced that evolution occurred, although I have no idea where, or how, life began, and I am convinced that the wide array of living organisms that we see around us, and the abundant examples of other life forms we know from fossils, all came about by mutation and selection. However, it is not possible to carry out experiments over time scales of millions of years to test my assumptions. We know that simple organisms that are abundant, and reproduce rapidly, undergo evolutionary changes over short time scales, and similar changes must occur, or have occurred, in multicellular organisms.
What is clear from the acceptance of Forbes' hypothesis is that we must be critical of established views, yet anyone proposing an alternative explanation will feel the weight of the scientific establishment at their back (ask James Lovelock). History shows that scientific explanations change with time and that must still apply – I wonder how many of our accepted theories, and non-testable hypotheses, will be accepted in the future?

[1] George Wilson and Archibald Geikie (1861) Memoir of Edward Forbes, F.R.S.: Late Regius Professor of Natural History in the University of Edinburgh. Cambridge, Macmillan and Co.

[2] Daniel Merriman (1963) Edward Forbes – Manxman. Progress in Oceanography 3: 191- 206.

[4] Thomas R. Anderson and Tony Rice (2006) Deserts on the sea floor: Edward Forbes and his azoic hypothesis for a lifeless deep ocean. Endeavour 30: 131-137.

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