Fontenelle replies that art and cultivation exert a much greater influence on human brains than on the soil; ideas can be transported more easily from one country to another than plants; and as a consequence of commerce and mutual influence, peoples do not retain the original mental peculiarities due to climate.

This may not be true of the extreme climates in the torrid and glacial zones, but in the temperate zone we may discount entirely climatic influence.

The climates of Greece and Italy and that of France are too similar to cause any sensible difference between the Greeks or Latins and the French.
Saint Sorlin and Perrault had argued directly from the permanence of vigour in lions or trees to the permanence of vigour in man.

If trees are the same as ever, brains must also be the same.

But what about the minor premiss?
Who knows that trees are precisely the same?
It is an indemonstrable assumption that oaks and beeches in the days of Socrates and Cicero were not slightly better trees than the oaks and beeches of to-day.