Final answer:
Yes, it is true that the Olmec were the earliest known culture to develop in the Gulf Coast of Mexico, flourishing from 1200 to 400 BCE and influencing later Mesoamerican civilizations.
Step-by-step explanation:
The statement that the Olmec were the earliest known culture to develop in the Gulf Coast of Mexico is indeed true. The Olmec civilization, often regarded as a "mother culture" to later Mesoamerican civilizations, flourished from about 1200 BCE to approximately 400 BCE. They are well known for their major works of art, such as the giant head sculptures and the pyramid in La Venta, but they also developed intricate systems of governance, trade, and religion, greatly influencing subsequent cultures like the Maya and the Aztecs.