Final answer:
Natural selection has shaped the female pelvis to be wider and shallower to aid in successful childbirth, which is an example of the pelvis adapting to reproductive fitness. This is part of sexual selection, where traits that enhance reproductive success are favored, even if they don't benefit individual survival.
Step-by-step explanation:
The effects of natural selection on the female pelvis are significant in terms of reproductive fitness. Over generations, females with a wider pubic angle and a larger diameter pelvic canal experienced more successful childbirths. Consequently, these features were passed on to their offspring, demonstrating how natural selection shapes anatomical structures for specific functions. The female pelvis is lighter, wider, shallower, and has a broader angle between the pubic bones than the male pelvis, adapting over time to the needs of successful reproduction.
In the broader scope of evolutionary biology, these changes in the pelvis also exemplify sexual selection, a process where certain traits become preferred because they enhance an individual's chances of attracting a mate and having offspring. Sexual selection may sometimes lead to traits that are not necessarily advantageous for survival but are beneficial for reproduction. An example in another context is the peacock's tail, whose its size and coloration, while disadvantageous for escaping predators, attract mates and hence are favored sexually.
These evolutionary processes, including natural and sexual selection, highlight the intricate relationship between physical anatomy, reproductive success, and survival, echoing across various species.