All species change over generations. 100,000 years ago humans did not have widespread lactase persistence mutations. When some humans started pastoral agriculture, raising cattle, sheep, goats etc. Today the descendants of those pastoralists have lactase persistence mutations, which enable adults to digest milk, as supplied by cows, sheep, goats. Those mutations are present in about one third of the current human population.
Evolution happens and can be observed if you are prepared to see it.
How long is a generation? For bacteria it can be about 30 minutes. Small animals take weeks or months. Elephants take longer than humans.
The chance I gave was the chance of reproducing or not. By observation the chance of any individual reproducing is greater than 50%, because we can observe that most populations are steady over time. That means that on average every individual has one offspring that reaches reproductive age and itself reproduces.
In my scenario half the individuals have 0 offspring and half have 2 offspring. That gives the observed one descendant on average per individual. That maintains a steady population.
Over time, my scenario does indeed produce 1,000 heads in a row, because any tails thrown are eliminated. That mirrors the face that all of your ancestors succeeded in reproducing. None of them failed, as shown by your presence here today.
As the saying goes: "If your parents didn't have any children, the chances are that you won't have any either."