The University of Michigan has done a release for a new paper studying speciation between black and mantled howler monkeys, by Marcella Baiz and coworkers: “U-M howler monkey study examines mechanisms of new species formation”.
It’s a very nice paper.
I’ve been following research on hybridization between these species for a long time, because one hypothesis for their history involves possible adaptation to colder conditions by one of the species: “Howler hybrid hunting”.
I’m linking the release because I found the following passage to be written very clearly:
A species was once defined as a group of actually or potentially interbreeding individuals that are reproductively isolated from other such groups. The concept of reproductive isolation is key to that definition and means that despite any hybridization, true species maintain their uniqueness.
However, the modern view of what a species is does not require full reproductive isolation, and hybridization has been discovered to be quite common in nature.
This is such a clever way of phrasing. “A species was once defined as…”.
Of course this phrasing is the biological species concept, which everyone learns in introductory biology, still today. It’s not a thing of the past. It’s just that biologists who work with closely-related animal species cannot define them based on postzygotic isolation. The instrumental examples that most people think about when they think of species are all instances of hybrid sterility or inviability.
Most people are less familiar with the hard cases, yet that’s what biologists who focus on speciation must study. During the last fifteen years, the growth of genetic sampling of wild populations has made it possible to examine hybridization to a greater extent. Biologists are finding hybridization almost everywhere.
That message hasn’t gotten out to the public as widely as it should.
Ancient DNA findings have brought hybridization to the foreground with humans, elephants, bears, and a few other groups. Findings about hybridization have really been the low-hanging fruit for ancient DNA, because with our present statistical approaches, ancient hybridization is of the things that can be examined with very small or unique samples. The statistical ease of testing the hypothesis of hybridization has shaped people’s research agendas – they are choosing museum specimens and geographic locations where hybridization is a relevant hypothesis to test.