Charles Marie de la Condamine was the first Frenchman scientist to travel through Amazonia. He was sent to South America in 1735 by the French Academy of Sciences to calculate the diameter of the Earth at the equator. On the way home to France, he traveled down the Amazon river and wrote many notes about the strange animals, plans, and customs of native Indians that he encountered along the way. His stories of electric eels, strange new plants and drugs, and exotic Indians caused great interest throughout Europe.

In the 18^th and 19^th centuries, early scientists were unsatisfied with traditional explanations, which explained everything in religious terms, or by ancient superstitions. Instead, the scientists were determined to study and to find out for themselves how our world works. They invented what we call “scientific method”. This is the way that scientists investigate and learn things – gathering information through careful observation and experiments, and recording everything that they see.

Charles-Marie La Condamine studied at the Jesuit College of Louis-le-Grand in Paris. There he was taught mathematics by Père Louis Castel. On leaving the College he decided to take up a military career and, when war broke out with Spain he joined the army. He distinguished himself with his bravery at the siege of Rosas in 1719 but decided that army life did not suit him.

At this point La Condamine made contact with scientists in Paris and became a member of the Académie Royale des Sciences in 1730. The quite life in Paris did not suit him either and he sailed on a voyage to Algiers, Alexandria, Palestine, Cyprus and Constantinople (now Istanbul) where he spent five months. On his return to Paris he published mathematical and physical observations of his voyage.

The Académie Royale was impressed and sent him on an expedition to Peru. In April 1735 La Condamine set out on the expedition to Peru to measure the length of a degree of meridian at the equator. Bouguer was a member of the same expedition and its third scientific member was the leader of the expedition Louis Godin. The three finished their journey by different routes, La Condamine going overland from Manta, the other two sailing to Quito where they joined up.

The three were soon involved in disagreements. Godin began to work on his own while La Condamine worked with Bouguer. In 1741 Bouguer discovered a small error in their joint measurements and these two fell out when Bouguer refused to allow La Condamine to recheck the results. Now all three made independent measurements, the work being completed in 1743. The three returned by different routes.

In 1743, eight years after setting out from France, La Condamine began his return journey, which included a four-month raft journey down the Amazon River. His was the first scientific account of the Amazon, which he published as Journal du voyage fait par ordre du roi a l'équateur (1751). However, before he returned to France he planned one more adventure. Having heard of the wonders of the Amazon, La Condamine decided that he wanted to see it for himself. Therefore his route home would involve crossing the Andes, descending the great river down to the Atlantic coast, and then catching a ship to France by way of Cayenne in French Guiana. Accompanying La Condamine on this journey would be his friend, the hospitable and adventure-seeking Don Pedro Maldonado.

The journey down the river was much easier than it had been for earlier travelers such as Orellana and Pedro de Teixeira thanks to Missions which had been established along the river by Jesuit priests. The travelers were able to receive food, lodging, maps, canoes and canoeists, and plenty of advice and other information along the way. This help meant that La Condamine and Maldonado had little to worry about in terms of their basic necessities – and freeing the scientifically-minded travelers to observe, measure, and record everything along the way. La Condamine's description of the Indians' lifestyle and of their hunting and fishing techniques is especially valuable, as it gives us another record of Indian cultures now lost to us. He was particularly interested in the Indians' knowledge of the plants and animals around them. 

La Condamine noted that some Indians fished by sprinkling a fine powder (extracted from local plants) onto the surface of the water. The powder would fall down into the water, causing the fish below to become groggy and rise to the surface. The stunned fish could then easily be scooped up by waiting Indians. Indian hunters often used arrows tipped with a powerful poison called curare. Even though the poison quickly killed the animal shot with it, it did not affect the Indians who ate the meat taken from the animal. The Indians had also discovered that if any of them received a curare wound (either accidentally from their own arrows, or in battle with a hostile tribe) they could cure the wound by applying salt or sugar, which counteracted the curare so that they did not die.

Although La Condamine marveled at the secrets about the plants and animals that he learned from the Indians, he was not impressed with the Indians themselves. He could not understand the Indians' who worked only as hard as they needed to, and spent most of their time relaxing or playing games. He couldn't understand the Indians' lack of foresight, seeing the Indians feast on enormous meals when food was bountiful then starve when it was scarce. The forest and rivers readily provided most of the things that they needed, so that the Indians had no need to work very hard. They had also learnt that trying to preserve food (without the aid of refrigerators) was useless in that hot tropical environment because the hot moist atmosphere caused food to spoil or rot very quickly – therefore it was best to eat the food when it was fresh then wait for the next hunt or harvest (because there was no winter, food could be harvested all year round).

La Condamine reached Cayenne on his journey home and spent five months there where he repeated Richer's experiments on the variation of weights at different latitudes.

By February 1745 La Condamine was back in Paris after his ten-year journey. He returned with many notes about the strange animals, plants, and customs of native Indians that he encountered along the way. His stories of electric eels, strange new plants and drugs, and exotic Indians caused great interest throughout Europe.  He gave 200 natural history specimens and works of art to Buffon.

Y Laissus writing in says:

The last survivor of the expedition, La Condamine, who was a less gifted astronomer than Godin and a less reliable mathematician than Bouguer often received the major part of the credit, probably because of his amiable nature and his talent as a writer.

La Condamine was a close friend of Maupertuis for many years. He spent much effort in the last part of his life campaigning for inoculation against smallpox. His passion on this topic was partly due to the fact that he had suffered from smallpox as a child.