You're Not Fully Human Until You're 18

First question:

From an evolutionary standpoint, what differentiates humans and animals?

Answer:

The historical great ones—particularly Kant, but also to at least some extent Aristotle, Aquinas, Hegel, Bradley, Mead, Prichard, etc.—will tell you it is moral thought. And if you think about it, you'll find the distinction makes sense. Some animals might be capable of rational thought, or may express human-like emotions, but animals are never capable of moral thought, of forming moral judgments.

Only humans do that.

Moral thought distinguishes humans from animals, and moral thought enables humans to act autonomously. It's what gives us rights, as opposed to animals.

Next question:

Why do we not allow individuals less than 18 years of age to participate in certain activities without their parent's/legal guardian's consent?

Answer:

Because adolescents' brains are such that they are not yet operating morally enough and they, thus, may make the wrong choice; that is, the choice that is not in their best interest. Not to mention, if young enough, they may be incapable of making a choice at all.

Final questions:

If individuals less than 18 years of age are incapable of moral thought, why do we still respect their autonomy by getting consent from their (morally thinking) parent/guardian, instead of coercing them to do what we want? Or, if a parent/guardian is overstepping their bounds and is harming a child under 18, why do we think it is ideal for CPS to step in and protect the child's autonomy, rather than letting the parent/guardian disrespect the child's autonomy, or letting the child fend for him- or herself?

Answer:

Because the potential for moral thought in the adolescent is there. We recognize that once they develop out of adolescence they will be capable of moral thought, capable of acting autonomously. We respect and protect (with the legal system) what does not yet physiologically exist, but will one day. To say "one day" is 18 years old is a bit of an arbitrary cut-off point, but it gets the job done. Most people are pretty grown-up and physically/chemically developed at that point. Brain circuitry and all. (I remember Nat Geo wrote an approachable article on the developing brain topic back in 2011.)

Do you see my point? (Sorry to drop another question on you. That really is the last one.) According to "The Greats" what makes you human is moral thought. According to the current US legal system (among others), as well as neuroscience, you are not fully capable of moral thought until you are 18 or 21. So, hate to break it to you youngsters reading this, but you are not human until you are 18.

From all this, it follows that:

We must (logically) respect and preserve the lives of the unborn, from conception to birth, because, just like adolescents, they are potential autonomous agents who will one day (you know, when they are fully human at 18 or 21) be capable of moral thought.