It does not include plant sources.
When using the term 'life form' I assume you are speaking of animals, bacteria, etc. Scientists take years to find their desired conclusion because of how the environment tends to change quite frequently (Depending on where the creature lives). The earth is constantly revolving and rotating, which causes changes in the environment. These changes affect the animals behavior, eating habits, and overall chances of survival. A factor that must also be considered is that scientists have to examine these creatures in their natural habitat which can be an issue depending on where they live. For example, if I were to study the behavioral patterns of a Leopard, it would be extremely difficult to do so because the Leopards are specifically keen at camouflaging in their environment. That would make observing its behavioral patterns very frustrating and time consuming. In a way, mother nature is always against us.
(Hope this helps)
Answer:
Dogs are wonderful human companions. They are the first species that humans domesticated and they have a long history of close relationships with people.
If you spend any time with dogs (I have two wonderful adopted dogs who shower me with affection and fur), then you see first-hand the many ways that dogs can respond to their owners. A dog may treat a stranger with suspicion, but dances with joy when its owner returns. Indeed, when one of our grown children returns after a long absence, the dogs respond with excitement.
