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Chapter 10
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
In the geological record on both land and sea, new creatures appeared slowly, one after the other. Once again, Darwin looked to Lyell, who noted that every year, new discoveries helped fill in the blanks between species and reveal the transition to be more gradual than previously realized. One of the lessons from the fossil record was that plants and animals from the same area do not necessarily change abruptly, all at once, or to the same extent. When species or groups of species disappear, they don’t come back, even if conditions change back to a favorable state.
Geology is the focus of yet another chapter in Darwin’s book. This might seem strange in a book that is ostensibly about biology, but Darwin’s theories involve the past and the passage of time—often geology is the best or even the only way to study these matters, particularly when it comes to the prehistoric past. Though Darwin has touched on the significance of extinction before, in this chapter, he expands on those earlier ideas.
Themes
On Extinction. Extinction and the introduction of new species are closely related processes. There is no universal law, however, determining how long a species will or won’t last before extinction. Though some authors believed that species had a fixed lifespan, Darwin didn’t. He did, however, believe that some factors played an important role in determining the lifespan of a species, including the presence of predators and competitors.
In general, Darwin avoids creating new laws to describe nature unless absolutely necessary. He is cautious about making claims he can’t support with evidence, which is why he doesn’t join with the opinions of other naturalists who believed that there were laws governing how long any given species would last.
Themes
On the Forms of Life changing almost simultaneously throughout the World. The geologists of Darwin’s day were surprised to discover evidence that many lifeforms changed almost simultaneously, even when separated by vast geographic differences. The findings were particularly striking for marine life.
Darwin attempts to follow the evidence wherever it points. This sometimes means accepting and accounting for strange observations that may at first be difficult to explain.
Themes
Natural selection, however, could explain why new forms of life seemed to appear simultaneously around the world. Since new species formed by having advantage over other forms, the new forms would gradually diffuse, ultimately spreading around the world. Thus, while the change did happen over time, when viewed on a large timescale, it would appear to have happened simultaneously.
The timescales involved with evolution are difficult for humans to understand and can often only be understood indirectly by studying evidence from the geological record. This is why many of Darwin’s disagreements with critics or even with allies often hinge on chronology.
Themes
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On the Affinities of Extinct Species to each other, and to Living Forms. Darwin looked at how extinct species could have potentially served as bridges between currently existing species. One particularly surprising case was the possible connection between modern birds and reptiles. Darwin found truth in the common belief that more ancient forms were more likely to have played an intermediate role in connecting modern forms.
Darwin has previously touched on the idea that intermediate forms were more likely to go extinct. Here, he extends the idea to note how this would specifically apply to modern species and how the links between different modern species (such as an intermediate species between birds and reptiles) may have gone extinct a long time ago.
Themes
Darwin observed that the animals alive during any one period in earth’s history will, on the whole, seem to be intermediate between the animals in the previous era and the animals in the succeeding one, although he allowed that in some genera, there were exceptions to the rule. As a result, fossils from consecutive formations in the same era were more similar to each other than fossils from more remotely separated formations.
The previous section looked at similarities moving horizontally along a hypothetical tree of life diagram. With this passage, Darwin extends the idea to apply similar principles to vertical relationships on the tree of life (i.e., relationships between current species, future species, and ancestor species).
Themes
On the State of Development of Ancient compared with Living Forms. Darwin hypothesized that if the ancient inhabitants of the world were pitted against its current inhabitants, the latter would survive because they are better adapted to earth as it currently exists. He admitted that such a conclusion was difficult to prove, but explained how he arrived at it. Despite its flaws and gaps, the fossil record does seem to show that modern lifeforms have become more organized on the whole than their ancient counterparts.
Darwin believes that natural selection results in organisms that are better adapted to their environment, and he believes that the environment of earth has changed over time. Therefore, he puts these two facts together to conclude that modern species are better adapted to the current environment than ancient species would have been.
Themes
Literary Devices
On the Succession of the same Types within the same Areas, during the later Tertiary periods. Darwin explained why, for example, terrestrial mammals like marsupials seemed to be endemic to areas like Australia. He explained that there was historical evidence of marsupials in other places like Europe, but that over time, the inhabitants of specific regions of the world tended to stay in their regions and pass on their unique characteristics to their descendants in the region.
Though Australia is a continent, it is also geographically isolated, which is why its species are often different from those found in the rest of the world. Notably, however, this isolation isn’t total, and there is some evidence of migration between Australia and the rest of the world. This demonstrates how widely animals migrated over time while also showing how local geography shapes natural selection.
Themes
Summary of the preceding and present Chapters. Darwin conceded that anyone who rejects the idea of an imperfect geological record might reject his theories, but he argued that available evidence pointed clearly to an imperfect record and that what did survive from this record generally lent additional support to his theories.
The imperfect geological record remains both a hindrance to Darwin’s argument (because it limits the amount of evidence he has to work with) and an advantage (because it allows for a wide range of possibilities in the past that have not been preserved).
Themes
