> In terms of human history, he's right. 6th-century BCE was not very long ago at all: that's less than a mere 3000 years. Humans have been around for over 2 million years.
3000 years is certainly long enough to take something out of "fad" status. I would challenge you to find another diet that follows specific rules that has been around for longer.
> Also, he's right about the skeletal record: archaeology shows that humans lost about 1 foot of height when they switched to agriculture.
Again - making broad, sweeping evolutionary correlations does not an argument make. You have absolutely no idea what specific shifts in eating, living or working habits resulted in skeletal changes. These are the same weak arguments proponents of the Paleo and Atkins diets make. Could you make a case for dietary changes effecting our evolution at the time? sure. Could you point to vegetarianism as the cause? Good luck with that.
> Yes, much of India is vegetarian, but Indians tend to be pretty short, but then when they emigrate to western nations and adopt more western diets, their kids end up dwarfing them.
Yet again with the generalizations. If we humor this for a moment, there is a much stronger argument for the correlation[3][4][5][6] of poverty levels[1] and height[2] than there is for levels of vegetarianism. In fact, there is data to show the opposite[7][8]. Poor diet in general results in impaired growth, not vegetarianism. I'm not even sure what you could argue would be missing in a vegetarian diet that would effect bone growth as most point to calcium in milk and vegetarians can drink milk...
1. https://ourworldindata.org/grapher/share-of-the-population-l...
2. https://ourworldindata.org/grapher/average-height-of-men
3. https://journals.plos.org/plosone/article?id=10.1371/journal...
4. https://www.reuters.com/article/us-health-children-height-po...
5. https://www.nature.com/articles/s41598-017-17880-3
6. https://adc.bmj.com/content/archdischild/76/5/463.full.pdf
7. https://www.ncbi.nlm.nih.gov/pubmed/1855500
8. https://www.ncbi.nlm.nih.gov/pubmed/9023462