Evolutionary pressure can take many different forms - population isolation, food scarcity, population dynamics, even the weather. When a population
is forced to adapt or die, the strong will survive. Given enough pressure and enough time, the genetic code changes and the organism passes on the
new genetic traits to the next generation.
Human evolution is measured in thousands or millions of years. But organisms like bacteria and viruses can adapt in a matter of days or even hours,
changing their genetic code to adapt to new challenges - like bacterial antibiotic resistance. Given rapid changes in the genetic code, speciation is
observed more frequently in these organisms:
Speedy speciation in a bacterial microcosm: new species can arise as frequently as adaptations within a species.
Koeppel AF1, Wertheim JO, Barone L, Gentile N, Krizanc D, Cohan FM.
Microbiologists are challenged to explain the origins of enormous numbers of bacterial species worldwide. Contributing to this extreme diversity may
be a simpler process of speciation in bacteria than in animals and plants, requiring neither sexual nor geographical isolation between nascent
species. Here, we propose and test a novel hypothesis for the extreme diversity of bacterial species-that splitting of one population into multiple
ecologically distinct populations (cladogenesis) may be as frequent as adaptive improvements within a single population's lineage (anagenesis). We
employed a set of experimental microcosms to address the relative rates of adaptive cladogenesis and anagenesis among the descendants of a Bacillus
subtilis clone, in the absence of competing species. Analysis of the evolutionary trajectories of genetic markers indicated that in at least 7 of 10
replicate microcosm communities, the original population founded one or more new, ecologically distinct populations (ecotypes) before a single
anagenetic event occurred within the original population. We were able to support this inference by identifying putative ecotypes formed in these
communities through differences in genetic marker association, colony morphology and microhabitat association; we then confirmed the ecological
distinctness of these putative ecotypes in competition experiments. Adaptive mutations leading to new ecotypes appeared to be about as common as those
improving fitness within an existing ecotype. These results suggest near parity of anagenesis and cladogenesis rates in natural populations that are
depauperate of bacterial diversity.
Human evolution is actually speeding up too.
From National Geographic News:
Human Evolution Speeding Up, Study Says
December 11, 2007
Explosive population growth is driving human evolution to speed up around the world, according to a new study.
The pace of change accelerated about 40,000 years ago and then picked up even more with the advent of agriculture about 10,000 years ago, the study
And this from Scientific American:
Culture Speeds Up Human Evolution
Analysis of common patterns of genetic variation reveals that humans have been evolving faster in recent history
By looking for wide swaths of genetic material that vary little from individual to individual within these sections of great variation, the
researchers identified regions that both originated recently and conferred some kind of advantage (because they became common rapidly). For example,
the gene known as LCT gave adults the ability to digest milk and G6PD offered some protection against the malaria caused by Plasmodium falciparum
"Ten thousand years ago, no one on planet Earth had blue eyes," Hawks notes, because that gene—OCA2—had not yet developed. "We are different from
people who lived only 400 generations ago in ways that are very obvious; that you can see with your eyes."