Successive Timelines

If I move from one place to another, then I am at one set of spatial coordinates (longitude, latitude and altitude) at time t1 and at another set of coordinates at t2. The entire three-dimensional spatial universe exists at both times. Similarly, I suggest, if the Scipios do not die at the battle of Ticinus in timeline 1 but do die at that battle in timeline 2, then the whole four-dimensional spatiotemporal universe exists in both timelines. This makes more sense, I think, than that a Neldorian time criminal causes a single timeline to split, thus effectively creating an entire new universe, merely by shooting the Scipios.

These are two examples of a successive timelines scenario:

"Delenda Est" by Poul Anderson
Timeline 1: Rome wins the Second Punic War.
Timeline 2: Neldorian intervention causes Carthage to win the Second Punic War.
Timeline 3: Time Patrol counter-intervention restores Roman victory in the Second Punic War.

Island In The Sea Of Time by SM Stirling
Timeline 1: Nantucket departs 1998 A.D.
Timeline 2: Nantucket arrives 1250 B.C.

In the second case, many Native Americans die of diseases imported by Nantucket and many Olmecs die fighting Nantucketers. Thus, many people die years or decades earlier in timeline 2 than they did in timeline 1. Thus, further, many other lives are affected, e.g., the Olmec champion killed by a Nantucketer would have lived longer and killed more people in timeline 1. Changes in peoples' lives change whether and when they procreate. Thus, before long, the entire population will be not only living in an altered history but also of a different genetic make-up. To give an example in the twentieth and twenty first centuries, there might be a blog written not by me living in a history which had a World War II but by someone else living in a history that did not have a World War II. We cannot know what would happen.

Comparing two timelines, there are three kinds of people:

before 1250 B.C., two identical world populations;
from 1250 B.C., an increasing number of people whose lives begin identically but then take a different course, e.g., by premature death;
some time later: two entirely different world populations.