Certain wild cereals, or grasses, contain edible components in their grain, botanically a type of fruit. Grains are small, hard, dry seeds, with or without attached hulls.
Some argue that from an evolutionary standpoint, grains are a relatively new addition to our diets and therefore should be excluded.
Undoubtedly grains have existed for many millennia, but the problem with harvesting had been that first of all these grains must be separated from the inedible grasses, requiring some winnowing process. Secondly, the wild grains usually shatter when ripe, dispersing the seeds, making collection difficult. Then the tiny hard grains would have to be further processed to avail digestion. Thus, patches of such grains in the wild may not have been favored by hominids until at least primitive hand tools were used and present near sites of grain-containing grasses.
Nevertheless, grains were apparently consumed well before animal domestication 10,000 years ago.
For example, a large amount of starch granules has been found on the surfaces of Middle Stone Age stone tools from Mozambique, showing that early Homo sapiens relied on grass seeds starting at least 105,000 years ago, including those of sorghum grasses. That’s more than 5000 generations ago.
Of course if one has celiac disease, gluten intolerance, a food allergy or sensitivity to grains, grains should be avoided.
Grains for brains (as well as other organs)
Whole grain includes dark bread, whole-grain breakfast cereal, popcorn, oats, bran, brown rice, bran, and many other examples.
Whole-grain foods contain fiber, vitamins, magnesium and other minerals, phenolic compounds and other phytonutrients, which may have favorable effects on health by lowering serum lipids and blood pressure, improving glucose levels, insulin metabolism and endothelial function, as well as alleviating oxidative stress and inflammation.
A meta-analysis of 15 cohort studies with nearly a half million participants revealed that whole grain intake was associated with a reduced risk of vascular disease.
There is an association between dietary whole grain intake and mortality; two large prospective studies of more than one hundred thousand participants indicated a significant life extension independent of other dietary and lifestyle factors.
The effect was pronounced up to one-half serving per day after which there was a leveling off. This is shown in the figure below, taken from the Wu et al. aforementioned article, where the mortality risk is plotted against servings of whole grain.
Relative Mortality Risk v. Whole Grain Intake
 Mercader, J. (2009), Mozambican Grass Seed Consumption During the Middle Stone Age, Science, 326.
 Anderson, J. W. (2003). Whole grains protect against atherosclerotic cardiovascular disease. Proceedings of the Nutrition Society, 62(01), 135-142. doi:10.1079/pns2002222.
 Tang, G., Wang, D., Long, J., Yang, F., & Si, L. (2015). Meta-Analysis of the Association Between Whole Grain Intake and Coronary Heart Disease Risk. The American Journal of Cardiology, 115(5), 625-629.
 Wu, H., Flint, A. J., Qi, Q., Dam, R. M., Sampson, L. A., Rimm, E. B., . . . Sun, Q. (2015). Association Between Dietary Whole Grain Intake and Risk of Mortality.JAMA Internal Medicine JAMA Intern Med, 175(3), 373.