Cracks down middle of wide pine planks

Q: I recently built a house in the Northeast and installed 11 inch wide T&G pine floors. Since then many of the boards have cracked along the board. I am not talking about gaps between boards, although we have many of those some even bigger than 1/4 in. Many of the cracks seem to be more closer to the edges than down the middle, although again a few have cracked down the middle. My contractor says this is normal with such wide boards but I can’t imagine that that is so.

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