Perhaps the best analysis I have seen is that the human body evolved over millions of years to eat a diet based on animal and fish products supplemented with seasonal vegetables, fruits, and even some grains. But it never evolved to handle to much sugar.

The missing component in this description is sugar. The body needs a minimum level of sugar to function but does not handle excessive amounts of sugar well over a long period of time. Before introducing to much sugar into our diet mostly in the form of refined carbs, many of our modern diseases were rare.

You can eat a vegan low carb diet or a protein low carb diet, both work. Genetics may influence what diet works best. But for the most part if the diet keeps your blood sugar under control, contains the necessary vitamins and minerals for good health, and you feel good, you are probably on the right track.