It’s called 6 degrees of separation. What it means is that we all have a common ancestor, and we all merely are branches of his genes. So we ARE all related.
If you look at it from a point of view, we are all children of God, and he is our father, he created us in his vision and mother nature gave birth to us.
Evolution, it would mean the first two apes that walked upright, male and female, started an offspring witch repopulated the earth. Some of the offspring mated with each other, while the others mated with todays apes and monkeys, but either way, it started with the two walking apes.
Or we could of been sent here by another planet? Say Humans exsisted on mars 4000 years ago? A meteorite hit the planet and destoyed all life, but in a last attemp to insure human survival, they sent Human cells, or DNA to planet Earth Via satelite or two astronauts, male and female, came and repopulated the earth. In other words, humans exist here because they came from another world, humans were the first aliens on the planet earth.
Alot could exsplain how all humanity is related, it could very well show why we have wars by reading how Cain killed Abel and how that was the first war among men. Cain killed Abel to show that men are killing their brothers when they have wars.
We may never know why it says that in the text of the bible, but I can insure you it is correct.