Did you know that although adobo is similar to the Spanish cuisine, it is 100 percent indigenous to the Philippines?
According to wikipedia, although it has a name taken from the Spanish, the cooking method is indigenous to the Philippines. When the Spanish colonized the Philippines in the late 16th century and early 17th century, they encountered an indigenous cooking process which involved stewing with vinegar, which they then referred to as adobo, the Spanish word for seasoning or marinade. Dishes prepared in this manner eventually came to be known by this name, with the original term for the dish now lost to history.
Even before the Spaniards came, early Filipinos cooked their food minimally by roasting, steaming or boiling. To keep it fresh longer, food was often cooked by immersion in vinegar and salt. Thus, early Filipinos could have been cooking its meat in vinegar, which is the basic process in making adobo. The process of adobo was an ancient method dating back to the Classical Period of preserving the pork and chicken meats. since there is no refrigeration at the time.
From the Chinese traders came soy sauce and thus this ingredient found its way into the meat being cooked in vinegar. Salt was slowly taken out from the recipe and replaced with soy sauce. However, there are adobo purists who continue to use salt in their adobo marinade.