Perhaps I misread, but to me 'tends to go up' makes it sound like an observed incidental effect, rather than a deliberate action.
Essentially I was saying 'sure, there's a correlation, isn't there also causation, aren't we the cause?' (which isn't the way around that's usually said!)
It was my suspicion that the change is a result of deliberate human action, but I am not a biologist or a farmer so that's not something I'm certain of. The trend, not the cause of the trend, is what seems more important in this case.
Everyone thought he was saying "are you sure it suggests that? It seems an odd to me because flesh grows over time, so it is a really bizarre conclusion if true!"
But OP didn't mean that. Instead this is what OP meant:
">> The successful seeds were all several centimeters long, 30% larger than modern date seeds, suggesting dates that were significantly larger than modern varieties.
"Actually, maybe it's not that the flesh was larger - but rather, the seed was! The flesh could have remained the same size."
OP then justified why he thought this was just as plausible, by mentioning wild bananas (Google image search "wild banana seed") as an example of large, ugly seeds in a same-sized plant.
Essentially I was saying 'sure, there's a correlation, isn't there also causation, aren't we the cause?' (which isn't the way around that's usually said!)