|Cogito ergo sum|
Logic and rhetoric
An ultimate end is a goal that is not subject to rational examination because there is no logical argument that can be made as to why a person should or should not pursue it. Logic and evidence are used to prove whether an action is a suitable means for attaining a given goal. They cannot prove whether the goal itself is worthwhile, except to the extent that the goal itself helps further another goal. Eventually, though, one reaches an ultimate goal that cannot be questioned.
For example, one person might prioritize pleasure over longevity, and choose to smoke even if it shortens one's life. A person could appeal to his desire for pleasure by saying that smoking has a lot of unpleasant effects. One could not, however, make an argument for why longevity is more important than pleasure if those are ultimate ends. It is simply a matter of preference.
Even if one argues that "it is logical to pursue longevity over pleasure because that would better further survival and reproduction, which natural selection favors," this is not persuasive because one has not explained, and cannot explain, why it is beneficial to do what will be favored by natural selection rather than what will bring the most pleasure. The meaning of life is a matter of opinion and not only is unsolved thus far by philosophers but is unsolvable even in principle because of infinite regression.
The gene is selfish, but the mind that the gene produced is also selfish. Occasionally the two will be in conflict, and one will prevail at the expense of the other. Natural selection could have the upper hand in the long term with regard to determining what behaviors will be encouraged, but the individual mind could be stronger in the short term and choose to act in disregard of what evolution will reward, if it does not care about those rewards.
An ultimate end is a type of "ultimate given".