I have a simple answer to this question which can be confirmed in any person’s daily life.
Simply, to be human is to seek to save one’s life and the life of another.
I’m going to deal with the latter, first.
First, saving the life of another: My son loves to scare the bejeebers out of me. If he isn’t trying to crowd surf (without the crowd) by diving head-first off the couch, or pulling household chemicals out from under the sink, then he’s stuffing some inedible object into his mouth and then giggling as I scramble to stop him.
Instead of becoming complacent to his consistently suicidal habits, I am on red-alert most of the time, actively working to curve his I-think-I’m-Superman behavior and channel his curiosity to non-fatal objects, such as toys.
And I’ve observed that I’m not alone in seeking to preserve my child’s or anybody’s life. In fact, our most basic human instinct compels us to do so. With regards to my children: whether we’re in public and another adult calls out to my child if they’ve disappeared around a corner, or we’re in the mall and the grown ups surrounding us take care to avoid knocking over my toddler who is absentmindedly darting through knees and couples, people always demonstrate a very human sensitivity to the vulnerable little person near them. I have never once encountered someone willing to callously kick a child over, or ignore them if the are in danger.
No, something triggers within us when we sense the potential for harm is imminent. I would say this is our human instinct to be on guard, whether consciously or not, to protect life-in-general.
Second, saving your own life. This is inextricably linked to safeguarding someone else’s life. Think about it. What makes us different from the magnificent wild beasts that roam the Savannah? The difference is that we care for those among us who are wounded; we don’t treat them as broken objects and leave them to become some predator’s meal ticket. Somehow we sense that our welfare is intimately tied up with theirs, and we begin to instinctively operate by the golden rule: we treat those in need the way we would want to be treated were we the ones injured (I think deep down, we know we all will need to be cared for at some time or another.)
If you want to put it another way, our empathy, our ability to look outside of ourselves and care for someone else is what humanizes us. This can help us understand what Christ meant when He said, “Whoever seeks to keep his life will lose it, and whoever loses his life will preserve it.” (Lk 17:33 NASB) It’s when we turn exclusively inward to seek our identity at the expense of loving those around us that we’ve missed our own humanity because we’ve betrayed our innately human ability to care for and sacrifice for others.
Therefore it is consistently human to want to save life: your own and someone else’s.
Those in the pro-choice camp want to argue that “preserving one’s life” (at least, the outer shell of a it and all its material accouterments) requires the ‘choice’ to kill an unborn baby. But their argument is inherently flawed because the so-called 'choice' of abortion is one whose essence contradicts the nature of the human being, who is naturally inclined to save and not eradicate life.
Therefore, only the pro-life perspective is consistently and fully pro-human.
This stands in sharp contrast to the view of an abortion providing giant like Planned Parenthood which justifies the taking of innocent human life because they see the bringing of that life into the world as a violence. And the same can be said for euthanasia: the pro -‘death with dignity’ camp operates under the perverse notion that we ‘impose’ life on those who are nearing its end.
This world view is the complete opposite of the pro-life, pro-human camp. It’s anti-human because its manifesto holds that life is somehow detrimental to us. We’re supposed to laud those that would end this burdensome gift-of-life, be it our own or someone else's.
But the pro-life movement marches on because its principles are confirmed in our inner-most being. Deep down we seek to truly preserve our lives and to flourish – even the 'choice' of abortion grows out of this desire, though it’s a decision that inherently violates it. And this is not only the case of abortion but to all life issues. One needs not look much further than within the confines of their own home, at their children or in the mirror for proof.