It is not always the magnitude of the differences observed between species that must determine specific distinctions, but the constant preservation of those differences in reproduction.
Interpretation
The importance of how differences between species are maintained through reproduction is more significant than their size.
Jean-Baptiste Lamarck emphasizes that while observable differences between species can vary greatly, it is the consistency in how these differences are passed on through reproduction that truly defines the uniqueness of each species. This highlights the role of heredity and reproduction in evolutionary biology, suggesting that the stability of traits is fundamental to the identification of species rather than just the extent of their differences.
In practice
In a biology class discussing evolution, this quote could be used to explain how traits are inherited.
Now this circumscribed power, which we have scarcely examined, scarcely studied, this power to whose actions we nearly always attribute an intention and a goal, this power, finally, that always does necessarily the same things in the same circumstances and nevertheless does so many and such admirable ones, is what we call 'nature' .
All knowledge that is not the real product of observation, or of consequences deduced from observation, is entirely groundless and illusory.
It is not enough to discover and prove a useful truth previously unknown, but that it is necessary also to be able to propagate it and get it recognized.
An Experiment, like every other event which takes place, is a natural phenomenon; but in a Scientific Experiment the circumstances are so arranged that the relations between a particular set of phenomena may be studied to the best advantage.
My fundamental premise about the brain is that its workings - what we sometimes call "mind" - are a consequence of its anatomy and physiology, and nothing more.
I've had a chance to fly a lot of different airplanes, but it was nothing like the shuttle ride.
To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.
We have no right to assume that any physical laws exist, or if they have existed up until now, that they will continue to exist in a similar manner in the future.
To those who ask what the infinitely small quantity in mathematics is, we answer that it is actually zero. Hence there are not so many mysteries hidden in this concept as they are usually believed to be.
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