So if we can't blame our ancestors for making us fat, then that means we can only blame ourselves.  Right?

Wrong!!

Now I know for a fact that you never volunteered to be fat.  And my hallucination is that you have probably tried numerous times to take off the weight with no lasting success.  So what is the problem. 

Why am I so weak!?  Why does my body want to be fat!!?

But you are asking the wrong questions.  What you should be asking is why is so hard to lose weight and so easy to put it back on?  What is the secret to being thin!?!