Evolution
speaking, variance within populations leads to the survival of individuals with favourable traits, who pass these heritable traits onto their offspring.
Darwin’s theory cannot, however, explain evolution by itself: while it explains external trends in species based on observations of biology, it does not offer a cell-level explanation, for example, for the process by which variation comes about, or traits are inherited. Insight into these is given by the process of genetics – mutations in genes can cause the variation for natural selection, 8 and Mendel’s law of inheritance can be used to explain how traits can be passed on and remain expressed in the phenotypes of offspring 9 – which is ultimately also useful to understand the trajectory of evolution over long periods of time. In recent years, the growing field of epigenetics – a term coined by Conrad Waddington in the ‘40s – has also incorporated factors other than genes into the expression of characters in an organism’s phenotype, which may themselves be heritable. Waddington uses the metaphor of a ball (predetermined genes) taking different paths down an ‘ epigenetic landscape ’ and so arriving at different points 10 – which is essentially the modern conception of differential gene expression. Some have even gone so far – controversially – as to call this Lamarckian. 11 Certainly, I would emphasize that, even if epigenetic factors effect evolution, they necessarily act secondary to natural selection. One problem troubled Darwin more than any other. He considered the seemingly instantaneous appearance of fossils, biologically very similar to animals today, at the start of the Cambrian period to be the greatest challenge to natural selection, which due to the small, random nature of changes, significant alterations must accumulate sequentially over many generations. To the absence of ‘ rich, fossiliferous ’ rocks in the aptly named pre-Cambrian, suggesting a suspicious lack of animal life, he had ‘ no satisfactory answer ’ . 12 More curiously, over the course of the 20 th century with the discovery of exceptionally-preserved soft bodied fossils (called Lagerstätten 13 ), parts of the supposedly lifeless pre- Cambrian were discovered to be full of animal life: only, this ‘Ediacaran biota’ mostly possessed no organs and were constructed modularly or fractally, 14 leading some to believe this was a ‘lost’ branch on the tree of life, or even lichens. 15 And after these organisms disappeared, soft-bodied Lagerstätten from the Cambrian ‘Explosion’ didn’t provide any clear answers either; though, as Darwin recogn ized, modern body plans emerge, so did a wealth of animals which seemed to be constructed of jumbles of mismatched body parts – the five- eyed Opabinia with its long ‘nozzle’ 16 or Hallucigenia apparently propped up on spines 17 (both from rocks from the Burgess Shale in Canada). Stephen Jay Gould – ever the colloquial science communicator – called these ‘ weird wonders ’ . 18 But far from just being oddities,
8 Dobzhansk 1937. 9 Fisher 1958. 10 Waddington1940. 11 Jablonka and Lamb 2002; Loison 2021. 12 Darwin 1859. 13 Conway Morris 1985. 14 Hoyal Cuthill and Conway Morris 2014. 15 Seilacher 1992; Retallack 1994. 16 Whittington 1975. 17 Conway Morris 1977. 18 Gould 2024.
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