Ventilation wasn't needed in the early times. Old houses were built in a way that fresh air can easily enter their openings and move around inside. Some modern houses in the countryside have similar design. But, most modern houses today are built so close together that proper ventilation becomes a must.
Natural ventilation. You might be one of those homeowners who think that opening windows is the best way to keep your residence well-ventilated. While this can allow some fresh in to your home, it can't guarantee the ejection of stale air inside your house. You might want to try creating a solar chimney. Through a solar chimney, the air is heated by the sun. The air becomes more buoyant and it rises up and out through vents near the top of your house. This lowers the pressure inside your house which draws fresh air in through especially placed inlet ports.
Exhaust mechanical ventilation. This strategy involves the use of small exhaust fans usually in the bathrooms. They operate either continuously or intermittently to exhaust stale air and moisture generated in such rooms. This strategy creates a modest negative pressure in the house which pulls in fresh air either through the cracks and other air-leakage sites. This is a simple strategy that is low-cost. One disadvantage of this though is the suction of random gasses that can pollute the air in your house.
Supply mechanical ventilation. In this strategy, a fan brings in fresh air, and stale air escapes through cracks and air-leakage sites in the house. The air supply may be delivered to one location, dispersed through ducts or supplied to the ducted distribution system of a forced-air heating system for dispersal. This can keep other contaminants from entering the house, but it risks forcing moisture-laden air into wall and ceiling cavities where condensation and moisture problems can occur.