These caves are carved out by underground streams. then the stream drops down, and the cave is left as a cavity for in some cases millions of years.

Over time the occasional huge rock falls in, but that is a 10-100 million year process.

Shorter term, a cave may develop an opening near the top which allows sediment to fall or flow in. If that happens long enough, you get a decent amount of sediment. That has not happened yet in Rising Star Cave.

Eventually that sediment influx may slow as the surrounding landscape changes through erosion and the cave opening is now in a high spot instead of a low spot (this is a 500K to million year process on this landscape). Then another opening may occur, in some cases.

If any water flowed down into these caves, it would carry sediment. That sediment is still there, or it has been incorporated into stone.

Any DNA would be associated with tissues, which would have carbonic anhydrase, which would catalyze the formation of carbonate mineralization until that mineralization blocked the diffusion of CO2 and carbonic acid. Flowstone might be an ideal site for DNA preservation. Maybe even better than sediments.

Datable layers would be nice.

What we need is techniques that can take materials apart and sequence every single strand of DNA, and also look for DNA-shaped holes formed in the calcium carbonate and other things from molecules like DNA.

Something like an atomic force microscope that took the rocks apart molecule-by-molecule, while keeping track of everything. That would take a lot of money to develop and would take a very long time to implement.

What is needed is a way to extract DNA from limestone/flowstone like what forms inside a cave (stalactites/stalagmites). That is the best ambient DNA as it would be found in layers possibly datable independently and fairly secure. This may be impossible, however, because of the chemical environment, but if there was something preserved IN the flowstone that would itself preserve the DNA that could possibly work.

If you could sift through tons of soil and get (via very advanced data processing) intact genomes, that would be worth doing, even if it cost a few billion.

http://science.sciencemag.org/content/early/2017/04/26/science.aam9695

http://www.nature.com/news/ancient-human-genomes-plucked-from-cave-dirt-1.21910

I’ve also read that individual humans’ brain sizes may vary by 2X. Perhaps, when dealing with different lineages of hominins, brain size comparisons — especially from small numbers of individuals — may not be as significant as previously thought to be.

I do not propose that this is so, I’m just wondering if it is a reasonable possibility. I can probably find the references if anyone is interested (but probably not as fast as Google).

We’ve tried to get DNA from other older material from a nearby cave, no much luck as far as I know. On the other hand, the person I was working with doing this turned out to be not impressive, maybe others have had better luck.

Since these hominins are relatively late, maybe there is hope there.

This is a unique resource that will be irreversibly destroyed if it is not handled properly. Having actual DNA sequences of these ancient relatives is crucial to understanding how they fit with the rest of hominin.