To expand a little on my previous post, you can expect wood to expand and contract about 3% over the course of a year with the typical changes in humidity in a house that is not humidity controlled. The typical oak or maple strip flooring is 2.250" wide so you can expect it to move .0675" and it has a tongue and groove joint that partially accommodates the movement. Your 11" wide boards would move by the same percentage which equals .330".
If you lay the floor when the wood is at its highest humidity, you can expect to see gaps of those dimensions when it is at its driest, usually in the winter with the furnace on a lot. If you lay the floor when the wood is driest, it tries to expand but cannot because it is butting against its neighbor. This crushes the cells in the wood and when it contracts you still get the gaps. It takes longer for the gaps to appear this way but they will still occur. Hopefully, you now see the problem, which is better than seeing gaps of more than a quarter of an inch in your floor.