 The conclusion that species are individuals has a number of interesting implications. For one, the relationship between an organism and its species is not a member/class relation but a part/whole relation. An organism belongs to a particular species only if it is appropriately causally connected to the other organisms in that species. The organisms of a species must be parts of a single evolving lineage. If belonging to a species turns on an organism’s insertion in a lineage, then qualitative similarity can be misleading. Two organisms may be very similar morphologically, genetically, and behaviorally, but unless they belong to the same spatiotemporally continuous lineage they cannot belong to the same species. Think of an analogy. Being part of my immediate family turns on my wife, my children and I having certain biological relations to one another, not our having similar features. It does not matter that my son’s best friend looks just like him. That friend is not part of our family. Similarly, organisms belong to a particular species because they are appropriately causally connected, not because they look similar.