From the first lines of The origin of species (1859), Charles Darwin (1809-1882) describes it as “mystery of mysteries”using a formula from the philosopher and botanist John Herschel (1792-1871). In this revolutionary work, the English naturalist achieves the feat of proposing the mechanism of natural selection that explains the evolution of species, without ever saying exactly what they are. “I’m not going to argue (…) Here are the different definitions that have been given of the term “species”. None of these definitions has completely satisfied all naturalists, and yet each of them knows vaguely what he means when he speaks of a species.warns in the second chapter of the book, where the term appears more than 2,000 times.
Therefore, it would be presumptuous to try to answer a question: what is a species? – something the British scholar, in his great wisdom, had seen fit to discard. Raising it, however, leads to illuminating fascinating aspects of the dynamics of life on Earth and proposing strategies to protect biodiversity, starting from its elemental “brick,” the species.
To illustrate the difficulty of the exercise, let’s delve deep into the forests of Madagascar, an island that features many unique aspects of flora and fauna. Lemurs, in particular, are not found anywhere else. Among them, the friendly lemur stands out. Large eyes that crown an 8-centimeter body and a 12-centimeter tail: this “mouse lemur,” as the Anglo-Saxons called it, is the smallest primate in the world. But also one of the most controversial in terms of its taxonomy, that is, its location on the tree of life.
Discovered in 1777, the classification of this animal was, until the end of the 20th centurymy century, object of relative consensus, with two species, it was estimated. One occupied the dry forests in the west of the island, the other inhabited the humid forests in the east. Appearance, climate, diet, geographical distance: the differences seemed pretty clear.
But the DNA revolution has happened there. The development of sequencing has made it possible to compare the genomes of specimens sampled at various points on the island. The observed divergences transformed the smooth landscape into a puzzle.
Immutable reality
In 2020, there were officially twenty-five species of mouse lemurs. You could say that this is good news for biodiversity. Except this fragmentation has led to the reduction of each population. And increase the fragility of each species. Barely described, six of them are in the “vulnerable” category of the red list of the International Union for Conservation of Nature (IUCN), eleven “in danger of extinction” and even four “in critical danger of extinction”.
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