Solid hardwood expands and contracts with changes in humidity and temperature. This is a natural characteristic of the material — not a defect. A dining table top may be fractionally wider in summer than in winter. Drawer fronts may fit differently between seasons. This is expected behaviour.
The pieces are designed and made to accommodate this movement. Tabletops are attached using threaded inserts or similar movable fastners, rather than fixed screws, allowing the top to move without the frame resisting it. Drawer runners are fitted with seasonal movement in mind.
If you notice small gaps or cracks appearing in very dry conditions — particularly in winter when central heating is running — this is usually the wood responding to low humidity. A humidifier in the room will help. In most cases, the gap will close again when humidity increases.