My Personal Summary
This book is about evolution through sexual section, or why organisms develop certain physical traits (“beauty”) as a result of mate selection.
The one big idea in this book is that evolution is not only driven by survival of the fittest, but also by survival of the most attractive.
There is evidence of evolution by sexual selection in many different species and this book focuses primarily on examples that can be found in various bird species since the author is an ornithologist.
- “Natural selection cannot be the only dynamic at work in evolution because it cannot fully account for the extraordinary diversity of ornament we see in the biological world.”
- The feathers of a peacock always bothered Darwin because it wasn’t clear how they improved an animals ability to survive and reproduce. It turns out that the feathers developed as a result of sexual selection – more brilliant feathers attracted females and increased one’s odds of reproducing.
- There are two schools of thought among evolutionary biologists as to why organisms develop “beautiful” physical ornaments: (1) these ornaments are a sign of good genes and vitality that females can detect in males or (2) these ornaments are simply aesthetically pleasing to females. Although (1) has received the majority of support among scientists over the past century, there is actually very little evidence in research that supports this. The author himself believes (2) is the correct school of thought.
- One example of evolution through sexual selection is club-winged manakins. This is a type of bird that has developed club shaped wings that allow it to make noises and songs through simply flapping their wings in a specific way that attract females during mating rituals. The development of this type of wing must be driven by sexual selection (females preferring it purely for aesthetic reasons) rather than natural selection because it actually hinders a manakins ability to fly since the wing shape is no longer optimally shaped for flight. The only reason this wing shape developed is because it increased a male manakins ability to mate and reproduce.
- Another example of evolution by sexual selection is in duck mating tendencies. It’s a fact that there are far more male ducks than female ducks, which means females have the ability to choose a partner based on aesthetic preferences (color, song, mating display, etc.). Once females mate with a male, they leg eggs which result in offspring. However, it’s well known that males who never get chosen by females often turn aggressive and force themselves onto females. Male ducks have evolved lengthy penis’ to penetrate the females but as a defense mechanism females have actually developed complex vaginas that make it much harder for unwanted males to successfully impregnate them. Females assume a certain position and use specific muscles to make it easy for wanted males to impregnate them. This is evidence that females do have aesthetic preference for males and will go to great lengths to avoid reproduction with males they find unattractive.
- Another example of evolution by sexual selection can be seen in the behavior of bowerbirds. The male birds in this species build bowers (structures made or plants, twigs and other materials) that they use as part of their mating ritual. It has been shown that the males who build the largest and most impressive bowers are the ones who most successfully reproduce with females. This is another example of behavior in males that has developed as a direct result of aesthetic preference from females.
- Modern science has allowed us to sequence the entire human genome and yet physicians still can’t predict whether or not an individual will develop heart disease later in life. Similarly, it’s tough to say that a female bird would be able to predict the health of their offspring purely off of the display traits of a particular male. It’s much more likely that female birds choose partners due to aesthetic preferences.