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Chapter 9
Themes
Key
LitCharts assigns a color and icon to each theme in The Origin of Species, which you can use to track the themes throughout the work.
Natural Selection and the Power of Nature
Reason, Argument, and the Scientific Method
Time and Progress
Collaboration and Science
Summary
Analysis
Darwin recounted some of his arguments from Chapter VI (where he answered his detractors), explaining again why it seemed likely that intermediate varieties died out quickly. The geological record seems to confirm this. Darwin noted that his mistake was often to look for intermediate forms that were directly between two current species when, in fact, it was better to look at how current species were related to an unknown ancestor species (for example, how contemporary fantail and pouter pigeons may have both descended from an ancient type of rock-pigeon).
Darwin’s continued emphasis on intermediate varieties shows how serious a challenge their absence in the fossil record potentially posed to his theories. Nevertheless, the situation also provides him with the opportunity to bolster his argument by providing greater nuance. Making the best of the data available to him, Darwin again turns to the abundance of examples present among currently existing species.
Themes
Literary Devices
Darwin allowed that it was theoretically possible for one current species to have descended from another current species (for example, the horse from the tapir), but this would involve one of the species staying unchanged for a very long period of time, and under natural selection, such a development was improbable.
Probability plays an important role in many of Darwin’s theories. As a careful scientist, he is cautious not to overreach with his statements. Instead of stating what definitively happened in the past, he generally prefers to say what is most likely to have happened. This goes hand in hand with the idea that natural selection is a process full of possibilities.
Themes
On the Lapse of Time, as inferred from the rate of deposition and extent of Denudation. Some of Darwin’s critics argued that the lack of intermediate forms in the fossil record was a sign that not enough time had passed for natural selection to have worked as Darwin argued it did. Darwin acknowledged that his own thinking on the issue of geological time owed a big debt to the geologist Charles Lyell.
Though the relationship between Lyell’s work in geology and Darwin’s work in evolution might not be immediately obvious, the connecting factor is the long timescales of both processes. Lyell’s work proved that the earth was very, very old and that geological changes generally happened very, very slowly. This long time scale also provided enough time for species to adapt and evolve very, very slowly.
Themes
Darwin explained how geological processes meant that some parts of the world had better preserved fossil records than others. This presented difficulties when using the fossil record to try to determine just how long it took for a new species to arise through natural selection.
Part of Darwin’s rhetorical strategy is to be honest about the shortcomings of the available data. This honesty helps him portray his arguments as even-handed, potentially making them appealing to a diverse audience of readers.
Themes
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On the Poorness of Palæontological Collections. Darwin wrote that even the world’s greatest museums had only a poor, imperfect collection of the geological record. In particular, massive geological shifts, due to factors like plate tectonics, mean that it is difficult to follow the geological record in a linear fashion. Moreover, only some regions had the right conditions to preserve fossils and become rich in them.
One of the hallmarks of Darwin’s theories is that he tries to make them comprehensive enough to account for different conditions in different parts of the world. Here, he notes how these different conditions could have led to different geological records, based on various factors that help preserve fossils.
Themes
On the Absence of Numerous Intermediate Varieties in any Single Formation. Even within a single geological formation, it is difficult to search methodically for intermediate varieties between species. There are strange cases where one species can be found on both the top and bottom of a formation but not in the middle. Though geological formations arose over a very long period of time, the time period often was not long enough to capture the change of one species into another.
Darwin suggests that the periods of time captured by the fossil record don’t match up perfectly with the periods of time over which evolution occurred in species. This means that the fossil record can seldom be used to chart an orderly progression of a new species as it diverges from its progenitor.
Themes
To get a perfect “gradation” between two different forms of a plant or animal, there must be a continuous regular geological deposit over a very long period of time. Such cases are very rare, and accumulation is more likely to be intermittent than continuous.
Darwin explains other geological factors that contribute to the difficulty of using the fossil record to try to reconstruct the linear development of new adaptations in a species.
Themes
Adding to the difficulties, it usually takes multiple specimens from multiple locations in order to definitively prove the connections between species. Many critics argued that, in fact, the geological record provided no evidence that intermediate forms even existed, suggesting that this means that species are immutable. While Darwin always acknowledged the imperfections of the geological record, he argued that there were cases of links in the geological record, while also acknowledging that it would be helpful to have even more.
Per the scientific method, results of an experiment should be repeatable. This is a challenge for Darwin because the imperfections of the fossil record mean that he often doesn’t have enough evidence to confirm some of his specific hypotheses and prove that they are repeatable. Nevertheless, Darwin makes it clear that even with all the geological imperfections, there is more than enough fossil evidence to support the theories about natural selection at the core of his ideas.
Themes
On the sudden Appearance of whole Groups of allied Species. Some of Darwin’s critics argued that because groups of species tended to suddenly show up in geological formations, this was evidence that species didn’t change. Darwin argued that such a view generally rested on too narrow a look at the geological record, and that considering other geological evidence from around the world usually complicated the picture.
As in other places where Darwin responds to his critics, Darwin generally takes a wider view of the situation than his critics do. By attempting to look at the full diversity of life on earth (and in this case the full fossil record), he is often able to reach surprising but well-founded conclusions.
Themes
On the sudden Appearance of Groups of allied Species in the lowest known Fossiliferous Strata. For Darwin, the more serious criticism involved some species of animals that began to suddenly appear in the lowest strata of fossil-bearing rocks. For a variety of reasons, geological strata from before the Cambrian era cover much longer periods of time. This long period of time would seem to suggest that there should be unusually rich deposits of fossils, but there aren’t, and even the most prominent geologists couldn’t fully explain the mystery.
The Cambrian Period, which began over 500 million years ago, was a time when diversity of life exploded and many new species formed. Study of geological eras from so many millions of years ago was a relatively new field in Darwin’s time, and the Cambrian Period remains a focal point for many who study evolution.
Themes
Darwin concluded that some aspects of the fossil record would have to remain a mystery, at least until new discoveries helped shed further light on the issue. Nevertheless, Darwin noted that prominent geologists like Lyell who once believed in the immutability of species had recently come around to ideas more similar to Darwin’s. He ultimately argued that in spite of the gaps in human knowledge, even the limited evidence that is available should be enough to diminish the concerns of his critics.
Though Darwin spends most of the chapter acknowledging flaws in the geological record, his ultimate point is that even with these flaws, there is enough evidence from the past to support his theories about natural selection and how new species formed and diversified slowly over time.
Themes
