Yes, science can use DNA to find the first human beings based on what DNA and the massive amount of information it holds. It hold the blueprints for all of the past in human history. The biggest issue is how to properly extract and read this data. This is come soon as they are already doing work on how to properly input data into DNA and extract it.
I do believe that we can and will be able to eventually use DNA to find the first race of human beings on the planet. They do this with a thing called genetic markers, and it makes perfect sense when they explain it. There will come a day when they find the oldest of all markers.
I don't think science can use DNA to find the first race of human beings. This is because the DNA of the oldest bones we can find is very fragile and reading it requires deeper analysis that we mostly likely cannot extract from it. It would be better to use DNA to focus on more moder issues like criminal cases, so it won't be a waste of resources.
I believe DNA could identify the first race of human beings, but since we pretty much understand DNA at this point, that's not really the difficult part at this point. Finding this first race of human beings is the difficult part. We need bones that still contain DNA to confirm this and there are a lot of what if's and uncertainties in finding them.
No, I do not think science can use DNA to find the first race of human beings, because it is impossible to determine what is first. In any event, the first race of human beings would have been so long ago, that it has been divided so many times, that it would be very hard to tell which DNA was original.