The son of Julio Tan and Apolonia Nieves Lim, Tan grew up in the City of San Juan, Metro Manila, where he had his early education at the Xavier School, a private Catholic college preparatory school for boys run by the Society of Jesus' Philippine Province, graduating in 1969. He majored in Biology at the Ateneo de Manila University, then transferred to the University of San Francisco, taking up the same degree. He eventually got a degree in veterinary medicine from the University of the Philippines Diliman in 1977, and from there he pursued a career as a veterinarian, which included a brief teaching stint at the veterinary school of Araneta University, before moving on "to human public health and pharmacology...and eventually, medical anthropology." He continues to use his skills as a veterinarian, however, working with such groups as the Philippine Animal Welfare Society and the Dog Scouts of the Philippines to promote animal welfare, and giving occasional advice as he goes about during his NGO work. Tan also works with the Ateneo de Manila University, "teaching doctors to be more sensitive to the social and cultural aspects of healthcare." He earned a Master of Arts in Anthropology from the Texas A&M University in 1982, and then obtained his PhD in social and political science from the Medical Anthropology Unit of the University of Amsterdam in 1996.
In 2012, Tan was elected member of the Philippines' National Academy of Science and Technology, the country’s highest advisory body in matters of science and technology. The citation that came with his election lauded him for his “sustained outstanding scientific research, teaching, advocacy and development work,” particularly in his “consistent efforts to revitalize scientific research on and in the use of traditional medicine, develop rational drug policies, and the social and behavioral dimensions of HIV/AIDS prevention and of reproductive health promotion.”
Appointment to the University of the Philippines Diliman Chancellorship
On February 27, 2014, the University of the Philippines Board of Regents appointed Tan to serve as the next chancellor of the University of the Philippines Diliman, where he currently serves as Dean of the College of Social Sciences and Philosophy. The announcement stated that Tan will serve as Chancellor from March 1, 2014 to February 28, 2017. When Tan presented his vision at the public fora for nominees to the UP Diliman chancellorship on Jan. 23, 2014, he noted that it was important for UP to “go beyond resting on laurels,” and instead live up to its mandate as a national university. The Tinig ng Plaridel, the official student publication of the University of the Philippines College of Mass Communication, reported that Tan said he "would focus on creating a safe, interconnected and nurturing environment that will enable students to shape the world around them." The Philippine Daily Inquirer quoted him as saying: The Philippine Collegian, UP Diliman's official student newspaper, reported that Tan had won the appointment by seven votes. Other nominees who got votes from the three remaining regents were incumbent UP Diliman Chancellor Dr. Caesar Saloma, and UP Center for Women’s Studies Director Dr. Sylvia Claudio. Tan's term ended on March 1, 2020 and was succeeded by former Vice Chancellor for Research and DevelopmentFidel Nemenzo.
Writing
Although he is now best known for his work as a columnist, Tan was already a well recognized writer among academics and NGO workers when he began his Pinoy Kasi columns for the Philippine Daily Inquirer in May 1997. Profiling him as an awardee Dr. Jose P. Rizal Awards of Excellence in 2005, the Manila Times and the Kaisa Para Sa Kaunlaran Foundation noted that:
"Pinoy Kasi" Column
In the maiden article of his Philippine Daily Inquirer column, he proposed "A middle way of looking at Filipino culture, avoiding one extreme of protracted Lenten self-flagellation that could see nothing good in the Filipino, but also being mature enough to talk about our faults." Regarding the choice of name, he explained further:
"Sense and Science" Column
In February 2013, Tan also began a blog for GMA News Online, titled "Sense and Science".