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The Institute’s thirty-first annual symposium was held on 15 & 16 September 1994. The twelve papers will be published in full as a single volume in association with Macmillan Press. Synopses of the first three papers appear in this issue of the Newsletter; the rest will follow in later issues.
Palaeontological research has shown that species can respond to environmental changes over time-spans inaccessible to living researchers but which are relatively short in geological terms. Some strata, for example an Ordovician sequence from the Builth inlier in Central Wales, permit a very fine detail of evolutionary change to be observed.
Fluctuations in the environment may have unexpected evolutionary results. Persistent phyletic evolution (“trends”) is more characteristic of narrowly fluctuating, slowly changing environments. Stasis - the persistence of form relatively unchanging over geological time, tends to prevail when environments are more widely fluctuating, until some threshold is exceeded at which time there is likely to be a sudden rapid evolutionary change. Species living in environments which fluctuate in the short term need to remain more “generalist”, with larger reserves of genetic variability.
Stress was a phenomenon understated in biology. Genetic studies of natural and captive populations made it clear that levels of genetic variability could adapt very quickly in the short term to environmental stress.
Adaptation to environmental stresses requires energy. Therefore the ability to adapt depends on an organism’s energy surplus. The amount of energy an organism dissipates as heat is at a minimum when the environmental temperature is within certain limits and often increases rapidly on one or both sides of a narrow optimal range. There may therefore be climates in which an organism has no energy surplus to adapt to the other stresses of life and into which the species cannot expand.
There appears to be an inverse relationship between metabolic activity and longevity. This may be because metabolic activity liberates free radicals which damage the body’s defence system. Organisms ought therefore to eliminate unnecessary metabolic activity. Stress in living organisms can be measured by reduced levels of metabolic energy carriers such as adenosine triphosphate and in historic populations by morphological asymmetry (of which more in a later paper).
Given the need to conserve energy, the investment some organisms - particularly the males of certain species - make in sexual ornamentation may seem surprising. However, in a population under nutritional stress there is likely to be a shift from monogamy to polygyny and this is promoted by complex mating patterns and social structures associated with sexual selection. The result is that scarce resources are channelled to a few dominant males who survive whilst the rest perish. Nevertheless, there is evidence that these ornaments enjoy their most extreme manifestations when stress is low, their size being restricted when stress is high.
Since stress-resistance and longevity are both mediated through metabolic energy carriers. it might be expected that genes for stress resistance also confer longevity and there is some evidence for this.
In Homo sapiens, which originated in the tropics where the low metabolic rate of modern populations compared with those elsewhere may be seen as an adaptation conferring heat resistance, body form may be regarded as an adaptation to climate. This may be a better explanation of the diversity of body types among Pacific populations than the usual reference to successive waves of settlement from South East Asia.