No both can be developed, but are you trying to specialize in anything? If your main event is say the 5km run, then you want to do more longer distance running and not be concerned with the fast twitch fibers but not stop sprinting. However, if sprinting is the main event, doing longer distance running, may hamper sprint performance to an extent by means of elongated slow twitch fibers which may become predominant.

A lot depends on the person's body composition. Maybe speak to a professional near you who can do an assessment.