Chapter 7 – Instinct

What is the point of chapter 7?

In chapter 7, Darwin goes into a discussion about instinct and how it changes. He specifically narrows the topic of instinct change to members of the same “class”. And also he does not talk about how instincts arise in the first place.

“I must premise, that I have nothing to do with the origin of the primary mental powers, any more than I have with that of life itself. We are concerned only with the diversities of instinct and of the other mental qualities of animals within the same class.”

As a note, this is the first time (and only time) I’ve come across him mentioning the problem of the origin of life in the book.

Just as he had been unable to offer definition of terms used in previous chapters, he also does not offer any definition of instinct in this chapter.

“I will not attempt any definition of instinct. It would be easy to show that several distinct mental actions are commonly embraced by this term; but every one understands what is meant, when it is said that instinct impels the cuckoo to migrate and to lay her eggs in other birds’ nests.”

He talks about the instincts of various animals in the chapter – aphides, dogs, cuckoo birds, slave ants, bees, and others.

Overall, I thought this was a very weak chapter and it did nothing to further his theory. And Darwin even admits this at the end of the chapter.

“I do not pretend that the facts given in this chapter strengthen in any great degree my theory; but none of the cases of difficulty, to the best of my judgment, annihilate it.”

I would agree that the discussion did not annihilate his theory, but if it didn’t strengthen it, is the only purpose then to just make the book longer?