Siblings born years apart can turn out to be similar to one another as adults, both in appearance and temperament, despite the fact that the parents have change

Siblings born years apart can turn out to be similar to one another as adults, both in appearance and temperament, despite the fact that the parents have changed and learned in that time, and they grow up with a different peer group. Someone born from the same batch of sperm, with parents at the same stage in their lives, is likely to be pretty similar. There may be significant differences at the individual level e.g. a child of a different gender is born to a family with certain ideas about gender roles, or stillbirths/miscarriages/disabilities occur or fail to occur due to this falling branch, but in aggregate, the people of the next generation will be pretty similar to the ones who would have existed otherwise. A lot of inventions get attributed to individual geniuses, but in many cases society was ripe for them, if Joseph Swan didn't exist, or became a ballet dancer instead, we would still have had electric light bulbs around the same time. I am not just the product of my parents, but of the centuries of history of society leading up to now. So in a few generations, you are right that all those small changes will result in all the people being different, society as a whole is likely to be fairly similar.