Spynx Riddle

I asked my roommate, about the Spynx riddle in Oedipus Rex play. “What goes on four legs in the morning, two at noon and three at evening?” He has no idea what is the answer for this riddle. Suddenly, one of my friend who also never heard this riddle before came into my room and I asked him the answer for this riddle. About 2 second, he gave me the correct answer; Human. My roommate is from Bachelor of Computer Science and friend of mine who gave the correct answer is from Bachelor of Education. So, there is a contrast between them. There is a reason why Bachelor of Education can answer the riddle. For me education is close to social and life while computer science is close to logic, fact and figure only. For me the most correct answer for the Spynx riddle will be human life-cycle. The answer is really related to education. This is the reason why my roommate can’t solve the riddle. Is it so? I hope somebody out there can give a response to the statement that I give above.