How did lice reach humans?
They are small and annoying—and very stubborn: lice are among the eternal pests, and they’ve felt very comfortable on humans and other mammals for some time. But when and where did this conquest begin? Researchers suspect: the parasitic relationship began in Africa.
sThey are almost constant guests in kindergarten and primary school: head lice. But these are by no means the only lice that infect humans and other mammals. The parasite-host relationship may have begun in Africa.
Elephants, dander and shrew elephants may have been among the first mammals to be infested with lice. An international team of researchers says in the journal Nature Ecology & Evolution that the common ancestor of these animals, belonging to the Afrotheria group, may have picked up the parasites from birds millions of years ago.
The lice then co-evolved with their hosts in the course of evolution or colonization of new groups of mammals. Many different species of lice are found in mammals, such as head and pubic lice and clothing lice on humans. Some types of lice feed on blood, others feed on the skin or secretions.
When and how the parasite invaded mammals as a host is not yet known exactly. To answer this question, researchers led by Kevin Johnson of the University of Illinois examined the genomes and trees of the louse family and their mammalian hosts.
Lice evolved from 90 to 100 million years ago
In all, they analyzed the genomes of 33 species of lice, and rearranged the genomes of 14 of them. Among them were the elephant shrew louse – a small African mammal that looks like a shrew – and the lint louse, a proboscis-related mammal also found almost exclusively in Africa.
Along with the elephant lice, which had already been sequenced, the researchers now had three species of lice from the Afrotheria group. Members of this group sometimes differ greatly in appearance, and their relationship is supported by the same genetic characteristics.
Investigations showed that the Afrotheria louse was the evolutionarily oldest mammalian louse. “This indicates that mammalian louse first appeared in this strange group of African mammals and then spread to other mammals,” Johnson said.
Lice likely originated between 90 and 100 million years ago and initially infected birds and dinosaurs. “And then, after the dinosaurs went extinct about 65 million years ago, and birds and mammals diversified greatly, lice also started looking for new hosts and diversifying,” Johnson said.
The switch from birds to mammals was probably very rare during evolution. But once lice learn to feed on or feed on mammals, they can move more easily from one group to another. When their families developed far from each other – for example, through geographic separation – lice evolved with them.