I thought of the issue of DNA degradation but forgot to mention it. I'm not sure DNA from Newton's time couldn't have been preserved intact to the present; even Neanderthal DNA in some cases remains intact enough to have been tested and found quite distinct from human DNA. However, preserving it even from Newton's time would require the right circumstances, creating an environment in which DNA degrades slowly... and I believe they just buried him as usual rather than putting any effort into any attempts to preserve him.

This is not accurate. Lactose tolerance is much more common in human lineages with a long history of dairy animal use, such as white people (although not exclusively them) but that has nothing to do with vitamin D, sunlight, or even skin color. Human skin produces vitamin D upon exposure to sunlight, and lighter skin is better at it, but that has nothing to do with milk consumption. (You might be thinking of the label on some milk containers, "vitamin D milk", but what that means is that vitamin D has been added to it as a dietary supplement... an ironic choice of food to put it in, because the people who need such supplements the most are also the least likely to consume milk, but that's what's being done. Natural milk is not a significant source of vitamin D.)