It's not really a competition for complexity within life, complexity arises naturally within life as a product of competition. Sometimes more complexity is mor

It's not really a competition for complexity within life, complexity arises naturally within life as a product of competition. Sometimes more complexity is more fit, and other times the added fragility makes the organism less fit... during the mass extinctions it was primarily the most complex organisms that died. The purpose of life as a whole is to spread this complexity to all parts of the Universe that can support it, so as to raise the overall complexity of the system. Another way to think about it is that life lengthens the path that energy needs to flow through in order to reach equilibrium (maximum entropy).