[oasisbob]

Have a source for that? Or even an example of a fruit where it's the case? It certainly isn't true for apples - heirloom varieties often have higher sugar content than modern apples. Modern apples taste sweeter than many heirloom varieties due to lower acidity, not higher sugar content.

Many modern cultivated fruits don't contain nearly as much sugar as they could because they're picked early, before their prime.

In the Northwest, Rubus armeniacus is an invasive species which has never been heavily bred, and is one of the sweetest fruits you can find - especially in late summer.

Grapes are one of the only fruits which have enough sugar to make wine with unless you use chaptalization. (Though some berries like Blackberries get close.)