1. (A) The theory of evolution by natural selection was developed by Charles Darwin in 1850. The theory was supported by his observations of the natural world during his five-year voyage from 1831 to 1836. (B) Evolution by natural selection happens when the environment changes, organisms best suited for the new environment survive and reproduce. The favorable adaptation is passed on to the next generation. Over time, more and more organisms will have a favorable adaptation, and the population will evolve.
2. Similar traits and features among various species can provide evidence of common ancestry. It is likely that traits and features shared by a group of organisms were inherited from a common ancestor.
Similar traits and features due to common ancestry are known as homology. By studying the homology of organisms, we can infer how they are related. The more similarities organisms share, the more closely related they likely are.
3. Habitat loss is the primary cause of higher extinction rates. Other causes include habitat changes, over-exploitation of wildlife for commercial purposes, the introduction of harmful nonnative species, pollution, and the spread of diseases.
4. Fossils are essential evidence for evolution because they show that life on Earth was different in the past than it is now. Paleontologists have used fossils to study the changes that have occurred in creatures as life has evolved on Earth. Embryology proves our modern theory of evolution by the similar structures found in embryos. The greater the similarity in structure, the more closely related the species are, and the more recent their common ancestor is. Natural selection is a mechanism that enables evolution. In a population with genetic diversity, the individuals that are better adapted and possess favorable traits eventually gain an advantage. Over time, the traits of these successful organisms dominate, causing the entire species to adopt these changes.
5. Every form of life on Earth interacts over time with other organisms, as well as with its physical environment. For that reason, the evolution of one species influences the evolution of species with which it coexists by changing the natural selection pressures those species face. The classic examples of this sort of evolution, called coevolution, are predator-prey and host-parasite relationships.