An excellent question for which I can only give you a partial answer, but I will give you more over time.
There was a strong trend towards consolidation in life that followed the demutualization of some of the larger companies. In property and casualty there has been some consolidation over time, but there's a wider distribution and I believe there is more entry and exit.
The other thing I would say, speaking now as an economist, is that one measure of the amount of competitive pressure is how many competitors there are, but it's not a perfect measure. So there are other indicators of how much competitive pressure there is, and a fair bit of controversy over how best to measure it.