Skip to content

Humans Increase Speciation?

March 24, 2014

Primula

We hear a lot about the loss of species in the Anthropocene–the present geological era, in which human existenced has substantially altered the content of our biosphere and the geochemistry of our planet. Much is made of the loss of biodiversity–perhaps ten or a hundred-fold increased rate of extinction of species, from megafauna such as tasmanian tiger and dodo, to vast numbers of marine phytoplankton (photosynthetic algae and bacteria). Practically speaking, nothing can bring these species back, despite herculean attempts to reproduce one or two; the mammoth, say, or certain wild cats.

Still, there is another view that, however regrettable the losses, some new species will arise–by the intriguing process of species hybridization. I am skeptical that the new biodiversity will “make up” for the losses, especially the functional loss of keystone plants and animals that maintain whole habitats. Whenever you fell Hometree, the loss of what lived there is incalculable. And, I’m skeptical of the claim that “Climate change also tends to boost regional diversity,” since rapid change commonly decreases diversity, owing to the failure to adapt. The problem with climate change today is not change itself but rapidity, the accelerating rate of change–global change at a rate faster then ever before, and only getting faster yet.

Nonetheless, the increasing movement of species amongst different locations will generate some new species through the process of species hybridization. The primrose Primula kewensis is an example of a flowering plant that arose in Britain, from two parent species arguably less interesting than their hybrid descendant. Similarly, the human species Homo sapiens actually arose through hybridization of previously divergent hominids including Neanderthal and Denisovan.

The hominids, like the primroses, were already closely related before they came together. In science fiction, Octavia Butler imagined the Oankali, extraterrestrial beings completely unrelated to humans, whose reproduction actually requires interbreeding with other life forms–and each hybridization produces a new species. On Earth, we don’t see this, although viruses (with their smaller genomes) show evidence of extensive gene exchange.

Clarification: At the level of the cell, distantly related organisms HAVE interbred–the bacteria engulfed by larger cells, evolving into mitochondria and chloroplasts. And similar assimilations occur today.

However, distantly related life forms with complex developmental body plans (such as vertebrate animals and vascular plants) do NOT hybridize unless recently diverged. If anyone knows otherwise, let me know!

2 Comments
  1. samldiener permalink
    March 25, 2014 2:58 am

    On your last point, that we don’t see speciation via hybridization on earth, my understanding is that Lynn Margulis’ theories regarding endosymbiosis (http://evolution.berkeley.edu/evolibrary/article/history_24) described major terrestial speciation events, including the incorporation of mitochondria and chloraplasts into eukaryotic cells, as occurring through hybridization (symbiotic merging between two distinct species). I thought that at the time Margulis proposed this hybridization hypothesis it was largely dismissed (early 1970s?), but now is more accepted as likely. Do I misunderstand either the process Margulis described or the current evidence for it?

    • March 25, 2014 9:14 am

      You are correct at the level of the microbial cell. At the level of the cell, distantly related organisms HAVE interbred–the bacteria engulfed by larger cells, evolving into mitochondria and chloroplasts. And novel “symbiogenic” assimilations of microbial life occur today. However, distantly related life forms with complex developmental body plans (such as vertebrate animals and vascular plants) do not hybridize unless recently diverged.

Comments are closed.

%d bloggers like this: