We learn about the remote past from fossils but the picture we can form is very incomplete. Chance governs the formation, preservation and discovery of fossils.
The more abundant a species was in nature, the more likely its remains are to be found: our early ancestors were not numerous, so their story is less well known than that, for example, of pigs.
And finding fossils themselves is like looking for a needle in a field of haystacks: selection of suitable locations will take the palaeontologist only so far - after that it is pure luck if a promising area yields the wanted fossils.
Reconstructing our family tree is like doing a jigsaw puzzle with almost all the pieces missing. Some seem to fit together; then another piece turns up and alters the whole pattern; and there are huge gaps.
But there are also patches where a few pieces clearly do fit, giving a clear picture for a portion of time. The nearer we get to recent times, the more pieces we have and the better our picture - but even relatively recently there are gaps and uncertainties.
