The Origin of Species: Chapter 1 Summary & Analysis

Causes of Variability. Darwin noted that, as a general rule, different varieties of domesticated plants and animals appear to be more distinct from each other than different varieties in the wild. Even the oldest domesticated plants and animals, like wheat, can be cultivated to yield new varieties.

Darwin suggested that there were two factors that led to variations: the nature of an organism and the nature of its environment. He introduced the concept of “indefinite variability” to refer to the slight variations between individuals of the same species. Over millions of years, these slight differences have the potential to become extreme. Differences related to the reproductive system were particularly important.

Some naturalists believed that all variations were connected to sexual reproduction, but Darwin noted that gardening, and particularly techniques like grafting, introduce variations that are rare in nature but common under domestication.

Effects of Habit and of the Use or Disuse of Parts; Correlated Variation; Inheritance. Darwin wrote that when organisms change their habits, it can produce an inherited effect. This means, for example, that the wings of a domesticated duck weigh less than a wild duck’s, because the domesticated duck doesn’t have to fly as much.

Darwin noted that sometimes traits were inherited together: for example, white cats with blue eyes were typically deaf, but mostly only if they were male. He suggested that, while many parts of the inheritance process were mysterious, ultimately it followed certain laws. He also clarified that he was only interested in variations between organisms that could be inherited, but that even with this limitation, the possibilities were endless.

Darwin didn’t have an explanation for why a child organism might inherit a trait from a grandparent that wasn’t present in either parent. He also didn’t know why some traits seemed to only be transmitted from males to males in domestic breeds.

Other naturalists in Darwin’s time noted that when domesticated animals were let out in the wild, their offspring gradually reverted to something more similar to the wild animals. Some took this as evidence that domestication could never add traits that would help an animal in the wild, but Darwin doubted this statement, although he admitted it was hard to prove either way. He believed that with an unlimited amount of time, it was possible to breed an animal for just about anything.

Character of Domestic Varieties; difficulty of distinguishing between Varieties and Species; origin of Domestic Varieties from one or more Species. Darwin wrote that domestic plants and animals often had a “somewhat monstrous character” compared to their wild counterparts, meaning that one specific part of them differed in an extreme way.

Darwin wrote about the difficulties of assessing differences between similar types of domestic plants and animals. For example, Darwin didn’t know whether the different breeds of dogs had all been produced through domestication of a single species or whether, in addition to the effects of domestication, dog breeds were also determined through the mixing of multiple distinct species. Darwin believed the latter view.

Some naturalists assumed that humans specifically picked animals and plants for domestication that were predisposed to develop variations and adapt to different environments. While Darwin believed variability was an important factor in determining a species’ suitability for domestication, he believed that many plants and animals that hadn’t yet been domesticated also possessed incredible potential for variation.

Darwin conceded that the origin of most domestic animals would probably remain obscure. He repeated his belief that modern dogs involved the mixing of several Canidae (a biological family that includes modern dogs and other dog-like creatures). Darwin looked at other species like cattle, sheep, horses, fowl, rabbits, and goats, weighing how likely it seemed to him that they descended from a single species or from a mixing of species.

Darwin considered ideas about the descent of species held by other naturalists, many of which Darwin found ridiculous. One naturalist, for example, believed that at one point, there used to be eleven different species of wild sheep in Great Britain alone—Darwin found this very improbable. Even with dogs, which Darwin himself believed came from multiple species, Darwin felt that some peers held views that were too extreme, like the idea that animals that looked like a pug or greyhound ever existed in nature.

Breeds of the Domestic Pigeon, their Differences and Origin. Darwin believed there was value in looking at specific examples in detail, so he decided to focus on domestic pigeons, obtaining samples of skins from as many varieties of pigeons around the world as he could. He found the variations among them extreme and surprising, particularly when seeing the pigeons from outside of England.

The pigeons often had fundamental differences in their anatomies, including different skeletons. The differences were so wide that if an ornithologist observing the domesticated pigeons had been told they were wild, he might have categorized them as different species or even in a different genus. Nevertheless, Darwin believed that most naturalists held the correct opinion: that all domesticated pigeons were descended from one original species: the rock-pigeon.

Darwin himself experimented with crossing some pigeons to see what would happen, and in particular, which traits were inherited. His findings seemed to confirm the idea that all pigeon varieties were descended from wild rock-pigeon, since the mixtures generally produced results similar to a rock-pigeon. Additionally, these hybrid pigeons all remained fertile, and modern wild rock-pigeons have proven capable of being domesticated. Given that pigeons have been domesticated since at least the time of ancient Egypt, there was plenty of time for domestic pigeon variations to arise.

Darwin acknowledged that his overview of domesticated pigeons was too short to fully cover the topic and that some people may still have trouble believing that all domesticated pigeons originated from one species. He also admitted that breeders—not only of pigeons, but of everything from cattle to rabbits to pears to apples—were often most likely to believe that different varieties arose from different species, because these experts are skilled at seeing differences. Darwin asked how naturalists, who know less than breeders about specific characteristics, can be confident that domestic plants and animals often descended from a single species.

Principles of Selection anciently followed, and their Effects. Darwin decided to answer the question posed at the end of the last section by going through the steps of how domestic species of plants and animals were produced. The important factor in domestication is that it results in adaptations that are useful to humans, not necessarily to the animal or plant itself. It was commonly known that these useful varieties of plants and animals didn’t arise all at once but that the adaptations were refined over successive generations.

The most expensive domestic animals with good pedigrees were generally created by never crossing different breeds, unless the sub-breeds were extremely similar. Propagating traits useful for humans wasn’t easy and often required careful attention to details—details so small that Darwin himself couldn’t see them. The same applied for plants, although in plants variations sometimes arose more quickly.

Some argued that the methodical breeding of plants and animals had only been a practice for about 75 years before the publication of The Origin of Species. But Darwin argued that despite the importance of modern innovations, the basic principles of breeding are ancient, and that ancient writings make reference to it, including classical Roman writers and the book of Genesis. Even people from central Africa, who went for a long time without contact with Europeans, had their own version of breeding.

Unconscious Selection. Darwin noted that while skilled modern breeders employ selection methods that are precise and intentional, for observing nature it is helpful to look at unconscious mechanisms for selection. Even inexperienced breeders and “savages” tend to unconsciously encourage the selection of animals that are better at leaving more offspring.

All of these unconscious changes accumulated to result in descendants that often seemed to bear little resemblance to their wild parents. Darwin believed that this explained why “uncivilised” regions like Australia and the Cape of Good Hope didn’t have any plants worth cultivating elsewhere—since their traits hadn’t been refined by civilizations with ancient origins.

Darwin reiterated that humans were the main force in driving domestication. He admitted that, for example, the first person to breed a pigeon with a slightly unusual tail probably couldn’t have predicted what a modern fantail pigeon would look like. Experts would be skilled at noticing differences, and so the changes in the pigeon’s tail would have been gradual over time.

Circumstances favourable to Man’s Power of Selection. Darwin wrote that he would weigh both the pros and cons of the proposition that humans have the power to drive selection in animals. To Darwin, it seemed that creating specific changes in a plant or animal involved both a lot of expertise and a large stock of the plant or animal in question to work with.

Darwin found that some animals were better suited for breeding than others. Pigeons were easy to breed quickly in great numbers, but cats were much harder to pair up for breeding—leading to less variation among varieties of domestic cats.

Some naturalists believed that domestic animals were reaching a limit in their adaptability for humans. While Darwin acknowledged that there were certainly limits to the possible adaptations of an animal, he didn’t believe that humans had reached that limit yet.

Darwin concluded the chapter by repeating and summarizing all his ideas about how different kinds of domestic plants and animals arose. He reasserted that selection was unquestionably the main force driving variations, regardless of whether that selection happened in a fast, methodical way or in a slow, unconscious way.