Aside from the prevalence of hybridisation, which does occur "naturally"
among many plant genera and occasionally even across genera, there is
precious little difference between wild and cultivated fruit species and
their varieties. Edible fruit evolved among plants as a seed distribution
mechanism. Every group of animals that eats fruit has shaped the evolution
of the fruit-producing species they feed upon, and vice versa. One of the
ways in which plants are adaptable as a group is in the fact that genetic
mutations can occur anywhere on the "body" of the plant, and the stems,
leaves, flowers, etc. that arise from those areas produce different
chemicals in different combinations. Thus, fruit and leaves can be different
in different areas on the same plant. These areas also produce seeds with
the "new" genes, and so this is one way in which new varieties are produced.
These varieties are selected based on the preferences of the animals that
eat it. Enough mutation occurs, new species are born (or new mental
categories humans can put other carbon-based life forms into). Such is life.
The only differences I can think of between cultivated and wild
fruit-producing plant species in relation to human consumption in the past
and present is a far reduced variety in modern western countries, and for
only one reason I have been able to come up with: The modern preference for
fruit that ships and stores well without bruising or going "off". Usually
this means fruit that has not yet ripened and/or a variety that is naturally
harder and sturdier. I've noticed that this also almost invariably means a
LOWER sugar content and a HIGHER fiber content among the most modern of
varieties (~50 years), especially when they are still somewhat unripe (as
most are, having been artificially "ripened" with ethylene gas and other
"ripening agents" in transit or during storage). Certainly not all plant
species that produce edible fruit produce fruit that is "shippable", and for
that reason most never make it to the display stands at grocery stores where
most of us get our fruit.
That there is significantly less variety among the fruit now consumed by
most westerners, I certainly agree with. But as a botanist, a keen observer,
and a competent researcher, I cannot agree that modern human-cultivated
fruit is any richer in carbohydrates or lower in fiber than "wild" species.

Ellie