In order to be descended from something via any sort of process resembling evolution, at some point, you have to be able to interbreed with the something.

Now, it was always a big mystery as to why there was never any evidence of crossbreeding between modern humans and neanderthals despite evidence of the two groups living in close proximity for long periods of time; one fairly good description of the problem resides here:

http://discovermagazine.com/1995/sep/theneanderthalpe558

And then, in the late 90s, they resolved the mystery by analyzing neanderthal DNA; the result they turned up was that neanderthal dna was about halfway between ours and that of a chimpanzee and pretty much everybody involved in these studies views that as eliminating the neanderthal as a plausible human ancestor, e.g.

http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0020080&ct=1

Until very recently some scholars have argued for the possibility that a tiny number of skull remains might constitute Neanderthal/human hybrids. A recent study however eliminates that possibility altogether.

The problem (for evolutionites) is, that all other hominids were further removed from us THAN the neanderthal. In other words, if you wanted to go on thinking that we are descended from hominids, you would have to produce some new hominid closer to us both in time and morphology THAN the neanderthal and the works and remains of such a creature would be all over the map and exceedingly easy to find, had he ever existed. There is, of course, zero evidence of it.

What that leaves as I see it is the reality that apes and hominids are one family of creatures, and we are another. Possible choices for an origin for modern man include:

1. Created here from scratch recently
2. Brought here from elsewhere in the cosmos
3. Genetically re-engineered from one of the hominids.

All three are plausible. There is overwhelming evidence that Mars was once inhabited, giving you at least one possible extraneous origin, and the genome of modern man shows unmistakable evidence of genetic engineering.

The idea of modern man having evolved on this planet, however, appears not to be defensible.