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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