His eldest brother, the Chevalier de Bazentin, strongly opposed, and induced him to abandon this project, though not without difficulty.
At about this time the two brothers lived in a quiet village[11] near Paris, and there for a year they studied together science and history.
And now happened an event which proved to be the turning point, or rather gave a new and lasting impetus to Lamarck's career and decided his vocation in life.

In one of their walks they met the philosopher and sentimentalist, Jean Jacques Rousseau.

We know little about Lamarck's acquaintance with this genius, for all the details of his life, both in his early and later years, are pitifully scanty.

Lamarck, however, had attended at the Jardin du Roi a botanical course, and now, having by good fortune met Rousseau, he probably improved the acquaintance, and, found by Rousseau to be a congenial spirit, he was soon invited to accompany him in his herborizations.
Still more recently Professor Giard[12] has unearthed from the works of Rousseau the following statement by him regarding species: "Est-ce qu'a proprement parler il n'existerait point d'especes dans la nature, mais seulement des individus ?"[13] In his _Discours sur l'Inegalite parmi les Hommes_ is the following passage, which shows, as Giard says, that Rousseau perfectly understood the influence of the _milieu_ and of wants on the organism; and this brilliant writer seems to have been the first to suggest natural selection, though only in the case of man, when he says that the weaker in Sparta were eliminated in order that the superior and stronger of the race might survive and be maintained.
"Accustomed from infancy to the severity of the weather and the rigors of the seasons, trained to undergo fatigue, and obliged to defend naked and without arms their life and their prey against ferocious beasts, or to escape them by flight, the men acquired an almost invariably robust temperament; the infants, bringing into the world the strong constitution of their fathers, and strengthening themselves by the same kind of exercise as produced it, have thus acquired all the vigor of which the human species is capable.

Nature uses them precisely as did the law of Sparta the children of her citizens.