The origins of living things, with their astoundingly diverse forms and functions, has fascinated thinking people since ancient times. Modern understanding of how evolution works arose from ideas conceived independently by Alfred Wallace and Charles Darwin, and famously developed by Darwin in his book, “On the origin of species1 published in 1859. The idea of living things changing progressively over time has existed since antiquity. Palaeontology and the idea of evolution as currently understood emerged in the 18th and early 19th centuries2. What Wallace and Darwin brought to the field was a credible mechanism for evolution: that small variations in the form and function of living organisms provide differences in their capability to survive and reproduce, leading to beneficial variations progressively increasing in frequency in populations in a process that Darwin termed “natural selection”. (“Survival of the fittest”, a phrase coined by Herbert Spencer3, captures the concept of natural selection effectively and has become a popular term for it.) Natural selection of variants and the adaptations they enable in living things is the basis of the emergence of species of organisms, their eventual extinction, and replacement by new ones.
“A problem for Wallace and Darwin was that neither of them knew what caused the variations to appear”
A problem for Wallace and Darwin was that neither of them knew what caused the variations to appear; understanding of that had to wait for the development of genetic science. The integration of natural selection theory with genetics during the first half of the 20th century provided a fuller and even more persuasive explanation of evolution: that the variations on which natural selection acts are caused by random physical, and consequently heritable, alterations to genetic material called mutations. This integrated mechanism (termed, The Modern Evolutionary Synthesis (MES))4 has repeatedly explained or been consistent with many phenomena observed in evolutionary research, and has long been widely accepted as the core mechanism of evolution.
An important consequence of the MES is the severe constraints it imposes on how variation and consequent adaptation of organisms can occur; it predicts that some processes are impossible, and this has long prevented serious consideration of them. However, powerful as the MES is, it is far from a complete explanation of how evolution works or, more generally, of the history of life. There is more to evolution than the MES; indeed, some biological phenomena are inconsistent with it, and this has stimulated alternative lines of research that have produced radically new knowledge and perceptions. One aspect of this concerns the links between environmental conditions and variation. Darwin and other contemporaries suspected that the environment might cause or influence variation, but their reasoning was restrained by the mechanisms of cell biology, heredity and embryological development not being understood at that time. Mutational randomness is not affected by environmental conditions; the environment can exert natural selection on variations once they have occurred, but cannot affect the types of variations that are made available. That isolation, in the MES, of variation’s origin from the environmental challenges and opportunities that it addresses is sometimes expressed as the phrase, “nature not nurture”. Here, we show how this assumption is becoming inadequate and, in doing so, is generating an extended view in which evolution can respond to environmental threat; evolution still involves the throwing of mutational dice, but often their effects are loaded. Throughout, we base our description on interesting examples of animal adaptation. We begin with an example that illustrates why the new thinking has emerged.
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References
- Darwin C. On the Origin of Species. John Murray; 1859. Later edition of this work available. [↩]
- History of evolutionary thought. In: Wikipedia. ; 2022. Accessed May 24, 2022. https://en.wikipedia.org/w/index.php?title=History_of_evolutionary_thought&oldid=1085632766 [↩]
- Herbert Spencer. In: Wikipedia. ; 2022. Accessed May 30, 2022. https://en.wikipedia.org/w/index.php?title=Herbert_Spencer&oldid=1085395822 [↩]
- Huxley J. S. Evolution: The Modern Synthesis. George Allen & Unwin; 1942. Later edition of this work available. [↩]