The Problem of Increasing Human Energy (1900)

When we speak of man, we have a conception of humanity as a whole, and
before applying scientific methods to the investigation of his movement
we must accept this as a physical fact. But can anyone doubt to-day that
all the millions of individuals and all the innumerable types and
characters constitute an entity, a unit? Though free to think and act,
we are held together, like the stars in the firmament, with ties
inseparable. These ties cannot be seen, but we can feel them. I cut
myself in the finger, and it pains me: this finger is a part of me. I
see a friend hurt, and it hurts me, too: my friend and I are one. And
now I see stricken down an enemy, a lump of matter which, of all the
lumps of matter in the universe, I care least for, and it still grieves
me. Does this not prove that each of us is only part of a whole?

For ages this idea has been proclaimed in the consummately wise
teachings of religion, probably not alone as a means of insuring peace
and harmony among men, but as a deeply founded truth. The Buddhist
expresses it in one way, the Christian in another, but both say the
same: We are all one. Metaphysical proofs are, however, not the only
ones which we are able to bring forth in support of this idea. Science,
too, recognizes this connectedness of separate individuals, though not
quite in the same sense as it admits that the suns, planets, and moons
of a constellation are one body, and there can be no doubt that it will
be experimentally confirmed in times to come, when our means and methods
for investigating psychical and other states and phenomena shall have
been brought to great perfection. Still more: this one human being lives
on and on. The individual is ephemeral, races and nations come and pass
away, but man remains. Therein lies the profound difference between the
individual and the whole.

—Nikola Tesla