[skoob]

Quoting http://en.wikipedia.org/wiki/Vitamin_C :

It is made internally by almost all organisms although notable mammalian group exceptions are most or all of the order chiroptera (bats), guinea pigs, capybaras, and one of the two major primate suborders, the Anthropoidea (Haplorrhini) (tarsiers, monkeys and apes, including human beings).

So not all primates.

[UseofWeapons]

Ok, look back at the wiki.

Do you know <i>why</i> you can't internally produce Vit C?

[jbri]

Because a mutation turned off our precursor's ability to do so, and (due to the abundance of vitamin C in their diet), wasn't immediately deleterous but instead managed to spread throughout the entire population.