And you can be absolutely sure they're all transitional leading to humans? How?
You can't know the ancestors of any fossil unless you extract DNA from the fossil and sequence it. Wikipedia has a good definition of transitional fossil:
A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group.[1] This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. Therefore, we can't assume transitional fossils are direct ancestors of more recent groups, though they are frequently used as models for such ancestors.
Transitional fossil - Wikipedia, the free encyclopedia
What we are doing with fossils is testing the theory of evolution. The fossils are the repeatable observations that are used to test the theory of what happened in the past. If humans evolved from a common ancestor with other apes, then there had to be a point along our lineage where populations had a mixture of human-like and ape-like features. Even if there were a side branch to our lineage, that side branch would still have features that were found in the direct lineage. As Darwin put it:
In looking for the gradations by which an organ in any species has been perfected, we ought to look exclusively to its lineal ancestors; but this is scarcely ever possible, and we are forced in each case to look to species of the same group, that is to the collateral descendants from the same original parent-form, in order to see what gradations are possible, and for the chance of some gradations having been transmitted from the earlier stages of descent, in an unaltered or little altered condition.
The Origin of Species: Chapter 6
"Collateral descendants" would be side branches that were not our direct ancestors. In the world of cladistics, no species is shown as being a direct ancestor of another:
What we are saying is that the theory of evolution predicts that there should have been species in the past 5 million years that had a mixture of ape and human features, and these fossils are evidence that the theory is correct. Just as importantly, the theory also predicts that you should NOT see fossils with a mixture of features that would violate a nested hierarchy. In the case of ape transitionals, fossils that have a mixture of ape and canine features would falsify the theory of evolution.
Each and every fossil is a test of the theory, and all of the fossils we find fit the predictions that the theory makes.
So, thus far, we have chimps who are our cousins but not our ancestors. They survived. Apparently, none of the other transitionals viewed them as competition. But all the species in between who are also our cousins didn't make it due to competition with H. sapiens.
Yes. Hunter-gatherer humans that seemed to prefer more open spaces did not compete with the chimp lineage which evolved in dense forest.
These seem to be pretty huge leaps. Macroevolution? A fork in the tree which leads to chimps from gorillas (though we still have both living among us today), but nothing left between chimps and us but fossils. What do we have between gorillas and chimps, or are they all fossils too?
If H. erectus was still alive, the gap between us and H. erectus would still be considered macroevolution. Macroevolution is simply speciation.
You asked for side branches of the human lineage that were still alive after diverging from another ape species. Chimps are just that. Chimps share more DNA with us than they do with gorillas. Chimps share a more recent ancestor with humans than they do with either gorillas or orangutans.
I understand your analogy, but I don't see how it applies to human family relations.
We share a common ancestor with chimps like we share a common ancestor with our cousins.
Would you say the same of humans? If so, would you mark that as a type of evolution?
I would say that all species are evolving, including humans. As to type of evolution, I guess I don't understand what you are referring to.