"On the Geological Succession of Organic Beings" is the tenth chapter of both On the Origin of Species by Means of Natural Selection by Charles Darwin and Darwin's Ghost by Steve Jones. In this chapter, Darwin and Jones continue to discuss geology. Much of the chapter is similar to the last one in that it consists of observations and explanations of the fossil record. On the other hand, this chapter delves more deeply into controversies surrounding the record.
One of the observations Darwin makes is that there tend to be periods during which many different species change and evolve much more than usual. This is somewhat contrary to Darwin’s idea of gradual change taking place in all species. There is an explanation for it, though. "When many of the inhabitants have become modified and improved," Darwin writes, "we can understand, on the principle of competition, and on that of the many all-important relations of organism to organism, that any form which does not become in some degree modified and improved, will be liable to be exterminated." In other words, there are periods of time during which species compete vigorously, and either evolve or face extinction. This leads to big changes in a number of species at once.
This idea is related to the modern theory of "punctuated equilibrium," developed by Niles Eldredge and Stephen Jay Gould. Jones, in his version of this chapter, describes punctuated equilibrium as "the notion of evolution as stasis interrupted by sudden change, a pattern that might, perhaps, result from some intrinsic property of the organism, rather than of the environment in which it lives." Punctuated equilibrium is, in fact, an idea that could fit right into the previous chapter of The Origin of Species, "On the Imperfection of the Geological Record." It is an explanation of the tendency of the geological record to have many gaps. Punk eek, as it is sometimes called, argues that if species evolve a great deal in a relatively short period of time, fewer fossils will exist to record that evolution than if they took longer to do so. This, of course, fits our observations of the geological record, but it is still an idea that is controversial within evolutionary biology.
Darwin mentions another possible reason for our difficulty in understanding fossil formations. "[A]s the accumulation of long-enduring fossiliferous formations depends on great masses of sediment having been deposited on areas whilst subsiding," he writes, "our formations are almost necessarily accumulated at wide and irregularly intermittent intervals; consequently the amount of organic change exhibited in fossils embedded in consecutive formations is not equal." He continues with a metaphor: "Each formation, on this view, does not mark a new and complete act of creation, but only an occasional scene, taken almost at hazard, in a slowly changing drama."
After having taken another look at these difficulties in understanding the fossil record, Darwin moves on to the concept of extinction. Darwin explains that in most cases extinction is not sudden, but is preceded by rarity of a species. Here Darwin makes an interesting point related to the modern idea of endangered species. He writes that "to admit that species generally become rare before they become extinct—to feel no surprise at the rarity of a species, and yet to marvel greatly when it ceases to exist, is much the same as to admit that sickness in the individual is the forerunner of death—to feel no surprise at sickness, but when the sick man dies, to wonder and suspect that he died by some unknown deed of violence."
Earlier in this chapter, Darwin makes another statement about extinction. This one seems obvious to us now, but it is interesting to think that how at one time it was not. "When a species has once disappeared from the face of the earth," Darwin writes, "we have reason to believe that the same identical form never reappears." Believers in divine creation of unchanging species might have no problem with the idea that God could create the same species twice. An evolutionist could hold the idea that there are only a small number of possible species, so an extinct species could simply evolve again. Neither of these views is right, however. Evolution is so complex, and involves, we know now, so many different genes, that the odds against the same species evolving twice are astronomical.
Darwin soon comes to another important question: the question of whether more modern species can be said to be "higher," or better, than older, less evolved ones. Darwin notes that "naturalists have not as yet decided to each other’s satisfaction what is meant by high and low forms." This is still the case, but even so, Jones is able to answer the question by writing that "[t]he idea of evolution as a ladder is (or ought to be) dead, but life has certainly gotten more complicated since it began." Darwin has something more to add to this debate, though. "[I]n one particular sense," he writes, "the more recent forms must, on my theory, be higher than the ancient; for each new species is formed by having had some advantage in the struggle for life over other and preceding forms." In addition, Darwin notes that species from England introduced to New Zealand have competed successfully against native inhabitants and spread, while species from New Zealand introduced to England have not. "Under this point of view," he writes, “the productions of Great Britain, may be said to be higher than those of New Zealand."
In Darwin’s summary of his ninth and tenth chapters, he writes, "He who rejects these views on the nature of the geological record, will rightly reject my whole theory." Darwin’s views on geology continue to appear right, and thus support his theory as a whole. "For he may ask in vain," Darwin continues, "where are the numberless transitional links which must have formerly connected the closely allied or representative species." Creationists continue to use the absence of transitional fossils as an argument against evolution, despite the fact that Darwin addressed this very issue over 140 years ago, and did so through arguments that make sense within the context of our lives and in light of more recent experiments. As Darwin notes at the end of his chapter, "all the chief laws of palaeontology plainly proclaim… that species have been produced by ordinary generation: old forms having been supplanted by new and improved forms of life, produced by the laws of variation still acting around us, and preserved by Natural Selection."
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