Answer:
When two species share a large number of homologous traits, it is evidence that they share a recent common ancestor. Vestigial traits are those that no longer function in an organism. The presence of vestigial traits can also help determine relationships between species that possess homologous traits that still function.
Step-by-step explanation:
Homologous traits are similar traits that are found in different species which share a common ancestor. An example of a homologous trait is the forelimb that is found to be similar in humans, whales, and birds, of which the arrangement and structure of their various bones are somewhat similar. The hint is that these three must have evolved over time from a common ancestor. Furthermore, the larger the number of homologous traits shared by two species, the more concrete the evidence it presents that they share a more recent common ancestor. For example, salamanders and lizards share a number of homologous traits which can be traced back to a more recent ancestor.
Vestigial traits are traits or features that are no longer functional or has no known function, and are said to be a remnant part from a past ancestor, which serves as an evidence of the ancestral origin of an organism. For example, the presence of vestigial leg bones in some snakes suggests that they come from an ancestor that are four-legged. Another example is the tailbone in humans, which is said to be remnant part of a tail.
Vestigial traits common in organisms are those that are no longer functional and can be used in determining the relationships between species that possess homologous traits that still function, as stated in the example above. i.e. the tailbone and tail, the vestigial leg bones and legs.