The size and shape of the vertebrate skull can reveal a great deal about an animal's lifestyle and evolutionary relationships. Consider your own skull. If you put your finger in your ear and move your jaw up and down, you can feel the space near the hinge of your jaw. Nestled in this space are the tiny bones that make your hearing possible: the malleus, incus, and stapes. All mammals have these three ear bones, but reptiles such as this T. rex don't.
Where did ear bones come from?
Evolution often results in the co-option of a preexisting structure for a new use. Cite three examples from this chapter to support this statement.
Evolution can also result in the loss of a trait. Cite three examples from this chapter.

Verified step by step guidance

1. Identify the concept of evolutionary co-option, which involves the adaptation of existing structures for new functions. This is a key principle in understanding the evolution of complex traits.
2. Review examples of evolutionary co-option from the chapter. For instance, consider how the jaw bones of early vertebrates evolved into the ear bones in mammals, demonstrating the repurposing of structures.
3. Explore additional examples of co-option, such as the evolution of feathers in birds initially for insulation or display, which later became adapted for flight.
4. Examine the concept of trait loss in evolution, where certain features may become reduced or disappear if they are no longer advantageous. This is another important aspect of evolutionary change.
5. Identify examples of trait loss from the chapter, such as the reduction of hind limbs in whales, which reflects adaptation to an aquatic lifestyle, or the loss of eyes in cave-dwelling species where vision is unnecessary.

Key Concepts

Evolutionary Co-option

Evolutionary co-option refers to the process where existing structures or genes acquire new functions over time. This can occur through natural selection, where a trait originally evolved for one purpose is adapted for another. An example is the evolution of mammalian ear bones from jawbones in ancestral reptiles, demonstrating how structures can be repurposed for new functions.

Homologous Structures

Homologous structures are anatomical features in different species that originated from a common ancestor, reflecting evolutionary relationships. These structures may serve different functions in modern species but share a similar underlying anatomy. The presence of homologous structures, such as the forelimbs of mammals, birds, and reptiles, provides evidence for common ancestry and evolutionary divergence.

Trait Loss in Evolution

Trait loss in evolution occurs when a species loses a characteristic that was present in its ancestors, often due to changes in environmental pressures or lifestyle. This can lead to the reduction or complete disappearance of a trait if it no longer provides a survival advantage. Examples include the loss of limbs in snakes and the reduction of eyes in cave-dwelling animals, illustrating how evolution can streamline organisms for specific niches.