When I speak with audiences about our responsibility to bear in mind the needs of the generations that will come after us, a century and more in the future, I am often asked why we should care about people who do not even exist.

The first time I encountered this question, I had to puzzle before answering. Assuming that those unborn future generations bear no genetic link to ourselves—as the vast majority of them will not, even if we happen to have children—there is no biological reason for caring whether they flourish or suffer. Nor is there any practical reason to care for them, since the quality of their lives can have no direct effect on our own well-being.

What I realized, as I pondered this challenge from the audience, is that the impulse to care about the fate of unborn generations arises from my sense of taking part in the human lineage. We are born into a world filled with blessings as well as curses inherited from previous generations—mathematics and nuclear weapons, antibiotics and racism, art and war; and when we die we pass on a world either enriched or diminished by our having lived. Our big brains enable us to remember and learn about the past, and to imagine the future consequences of our actions. A failure to recognize our participation in this human lineage is to waste our distinctive gifts.

I feel deep gratitude for the goods we’ve received from previous generations, including the bounty and resilience of nature they have taken pains to preserve. Likewise, I feel deep regret over the legacy of damage those generations have passed on to us—from slavery, sexism, genocide, pollution, and the like. The regret prompts me to reduce the damage I might cause by my own way of life, and to resist the most damaging aspects of my society. The gratitude prompts me to help preserve the sources of our well-being—clean water and air, biodiversity, public lands, knowledge, art, democracy, among many other gifts—and to add whatever new goods I can fashion with my limited time and talents.

Caring about the fate of unborn generations—strangers who exist, as of now, only in our imagination—is an essential part of what it means to be human.