16 August 2012

Bugs Stay Bugs

Has anyone ever asked you, "If humans evolved from monkeys, then why do we still have monkeys?" Or maybe you have encountered this one: "If evolution happens, then why don't we ever see new species?" Such question are often asked by people who have no understanding of evolutionary processes and who may not even believe that such processes exist. The fact that anyone today, given the overwhelming evidence for biological evolution, would ask such questions is a depressing reflection of the poor quality of biological education in the United States.
[Introduction to Physical Anthropology, Tenth Edition, page 23]

My problems with the book are legion, but here's an interesting one relevant to this paragraph. The genus Homo appeared with Homo habilis, the oldest fossil of which, KNM ER 1813, is about 1.9 million years old. That means the genus Homo has been around for about 82,600 generations, during which time we went from this:

to this:

That's a significant change, and humans evolve slow, but bacteria evolve quickly (supposedly), which is why we see all this antibiotic resistance springing up (actually, those "super bugs" can only exist in modern super clean settings like hospitals; when put in a neutral environment they are easily outcompeted by their non-drug resistant counterparts).

Richard Lenski at Michigan State ran his famous long-term E. coli experiment that got him a spot at the National Academy of Sciences. In that time since the experiment started and his big discovery in 2008 his germs lived through 31,500 generations, not quite half the time it took to turn chimp-man into modern humans. E. coli is missing an enzyme called citrate permease, which would allow them to transport citrate trough their cell membrane in the presence of oxygen. The development of a gene, Cit+, necessary to transport citrate required the mutation seen at generation 31,500 and another mutation at generation 20,000. To this day (at least as of 2011) Lenski has not been specific about his Cit+ cells (even defensive and condescending when asked), but another study showed the existence of mutant E. coli that could perform the same trick did so by overexpression of an existing gene that allowed them to transport citrate in anaerobic conditions (citT). If Lenski's Cit+ cells are like the citT cells, then the only change was in the rate of gene expression, not the appearance of anything new.

In the same time it took Lenski's E. coli to (probably) alter the expression rate of a preexisting gene and develop the ability to digest citrate in aerobic coditions, under circumstances set up to pressure them to develop this change and food was given to them, Homo erectus had appeared and Homo habilis was gone. Erectus was significantly larger, had nearly doubled brain size, reduced sexual dimorphism, invented fire, likely had the ability for some form of speech, lived in the first hunter-gatherer societies, and spread out over most of Afro-Eurasia, and all under natural conditions, where there existed real competition, predators, and the reality of having to work for food.

Why don't we ever see new species then? We watch E. coli for now 50,000 generations under ideal conditions and essentially nothing happened, yet somehow there was a quantum leap in human evolution that no one was around to see. My question, then, is, if speciation happens why does it only happen when no one is looking? Better yet, why is speciation an experiment that can't be replicated?


Michael Behe paper (The Quarterly Review of Biology, Vol. 85, No. 4, December 2010) critiquing Lenski's experiment.

Evolution News article on the Lenski experiment.