Despite its title, the poem gives us only a handful of plain, physical details about people who lived long before us: they were short, they squatted for hours, they squinted, their teeth were bad. The speaker seems to be imagining pre-agricultural people, since their teeth are said to be better than those of "the farmers who followed them." The tone is matter-of-fact, almost like a field note, yet admiration slips in. These people "knew the right times for things" and could remember what they heard in a way we, shaped by reading, cannot.
The ending carries the sharpest feeling. The ancestors knew "every conceivable grief" but not the "small, dull" disappointment of buying a part that can be swapped for another. The speaker isn't simply nostalgic, since the ancestors suffered plenty. Instead there's a wry, wistful sense that modern life has thinned out even our sorrows. The mood is calm, dry, and quietly humbled.