The Origin of Species: Chapter 7 Summary & Analysis

Darwin announced his intention to use this chapter to respond to some miscellaneous critics of natural selection. Darwin believed that perhaps the most serious objections came from Heinrich Georg Bronn, a distinguished German paleontologist. Bronn thought it unlikely that a variety would live side-by-side with its parent species. He also believed that different species must differ not just in a single characteristic but in multiple ways. Finally, Bronn (and others) suggested that many creatures have characteristics that seem to be useless and therefore could not have been influenced by natural selection.

While Darwin acknowledged the validity of Bronn’s concerns, he cautioned against making sweeping generalizations about what was and wasn’t a useful characteristic. The ears of mice, for example, were listed by Bronn as an example of a trivial adaptation, but Darwin noted that these ears were full of nerves and that their size likely did play an important role.  Darwin also acknowledged that he had adapted his own views on the issue since the previous edition of the book.

A prominent zoologist named St. George Mivart was a critic whom Darwin respected and wanted to answer. Mivart had a couple objections, notably that a giraffe didn’t make sense under natural selection because the additional bulk added by its neck (requiring an increased supply of food) surely outweighed any potential advantages. Darwin argued that the increase in food was great enough to justify the neck and that perhaps the tall neck also helped the giraffe observe and fend off predators.

Mivart’s second objection was that if a giraffe is so well adapted, why haven’t all four-legged mammals developed a long neck like giraffes and, to a lesser extent, camels have? Darwin believed that this objection could be dealt with by considering the different geographies of different creatures’ environments. Another solution is considering how a feature like a long neck requires other body adaptations to be an advantage, meaning it would not be naturally selected for in all animals.

Darwin continued looking at some of Mivart’s other objections, including the idea that the jaw of a Greenland whale is so large and complex that it couldn’t have arisen through slight successive adaptations under natural selection. Darwin held firm in his disagreement, however, using the example of the shoveler-duck’s beak to show how a structure like a whale’s jawbone could have similarly arisen through natural selection. Mivart had other objections of a similar nature, and Darwin responded in turn to each of these with examples.

Ultimately, Darwin’s disagreement with Mivart was that Mivart believed drastic adaptations like a bat’s wings happened suddenly, rather than through successive variations as Darwin proposed. While Darwin acknowledged that in some ways Mivart’s view sounded reasonable, he ultimately believed it required making too many assumptions, and that there was not enough evidence in the geological record or in studies of embryos to suggest that it was valid.