Species of wood are as unique as individuals. It’s important when choosing a new wood floor to consider your climate and how one species behaves in your climate compared to another species. Wood is hygroscopic, and this means it adapts to the environment it is in. Some species are more stable than others which means they move less in service.
During the winter months with the heater on to maintain a pleasant environment, wood will shrink, and this is what creates the “gaps” you commonly see in the floor. There is nothing wrong with the floor and it is not defective, it’s simply shrinking due to the dryness in the air or low relative humidity. A humidifier is highly recommended for winter months. In the summer months, more humidity means the wood swells again and gaps typically close up. Depending where you live, a dehumidifier may be necessary in the summer months. Some woods shrink less than others and are more stable than others; if this is a critical point for you, then comparing species stability should be on your list of considerations in selecting the right species of hardwood for your new floor.