If that were true, then why is it that taking certain drugs like alcohol, that temporarily raises our ability to absorb endorphins thus making us feel euphoric for extended periods of time; eventually leads to depression, in which the body is unable to make the crucial chemical needed to endure happiness without the mind altering substance being present?
We lost the ability to synthesize it because we eat lots of foods that have naturally occurring vitamin C, and in turn after doing it for so long, our body has lost the ability to reboot that process back, and through multiple generations of reproducing, has become a permanent part of our genetic make up.
Much the same way a chronic/relapsing alcoholic can become a Chronic Depressive, even long after they have sobered up.