News release: “Infectious disease may have shaped human origins, study says.” June 4th, 2012.
Full text of the article in the news: Specific inactivation of two immunomodulatory SIGLEC genes during human evolution
Excerpt from the news release (with my emphasis):
Varki said it’s probable that humanity’s evolutionary bottleneck was the complex result of multiple, interacting factors. “Speciation (the process of evolving new species from existing ones) is driven by many things,” he said. “We think infectious agents are one of them.”
Speciation is driven by two things:
1. Nutrient availability establishes the ecological niche.
2. The metabolism of nutrient chemicals to pheromones establishes the social niche.
The news of this research extends the molecular biology of self / non-self recognition that is common to all species from microbes to man to the out of Africa theory of humanity’s evolution. It best represents how current knowledge of molecular biology can be used when people demand scientific support for theories.
We can now begin with the effect of pathogenic bacteria on intracellular signaling and stochastic gene expression. From microbial changes in gene expression, it may be easier to better understand the complex system-wide effects on the ability of multicellular organisms to recognize self / non-self differences in their pre-existing genetic variations.
Whether in unicellular organisms or multicellular organisms, the pre-existing genetic variations, which are responsible for self / non-self differences that determine what is commonly called “tissue type,” are a function of chemical recognition. Nutrient chemicals signal “non-self” to the organisms that ingest them. Bacteria ingest the DNA of a genetically dissimilar heterospecific, but not of a genetically similar conspecific (Finkel & Kolter, 2001; Palchevskiy & Finkel, 2009).
The ability to detect differences in the genetically determined chemical signals of other organisms in an ecological niche is essential to individual survival because nutrients ‘calibrate’ the survival of all cells. This calibration of intracellular signaling is essential to species survival because reproduction is required and sufficient nutrition enables it. But it is the metabolism of nutrient chemicals to pheromones that standardizes and controls reproduction in the context of the nutrient chemical-dependent ecological niche responsible for social niche construction or contraction.
In bacteria the ability of a species to maintain an ecological niche is determined by a function of pheromones called quorum sensing. Reproduction ceases and the social niche contracts before a colony exhausts its food supply. This fact makes it clearer that bacteria can detect and respond to genetically predisposed variations in their chemical signatures with behavior that enables adaptive evolution. This ability to sense and respond to chemicals is required in all organisms that have evolved and the model in bacteria extends to sexual reproduction (Shapiro et al., 2012). Adaptive evolution clearly is a function of sensory signal detection and appropriate responses to chemical differences. Most people recognize this sensory signal detection – even in microbes — as olfaction (Nijland & Burgess, 2010), or in other words, their sense of smell.
I reached the conclusion that olfaction and odor receptors provide a clear evolutionary trail that can be followed from unicellular organisms to insects to humans, in Human pheromones and food odors: epigenetic influences on the socioaffective nature of evolved behaviors (Kohl, 2012) . Evolutionary theorists, however, are still attempting to scientifically support refined theories of evolution like the modern synthesis (MS) and extended evolutionary synthesis (EES).
In all evolutionary theories there is scientific support for the role of nutrient chemicals and pheromones. For example, it is adaptive evolution that promotes foraging for new sources of nutrition that may have led our ancestors out of Africa. In contrast, is there scientific support for statements that the process of evolving new species from existing ones is driven by many things (i.e., not just via nutrient chemicals and pheromones)? If so, it is time for evolutionary theorists to detail how anything else drives speciation, or what other things drove humanity out of Africa. If nutrient acquisition and the metabolism of nutrient chemicals to species-specific pheromones does not cause it, what else is required for adaptive evolution?
Some people still think that ‘random mutations’ cause speciation. Are random mutations one of the many things Dr. Varki thinks was responsible for driving humanity out of Africa? Is there a model for that? Or is his comment on the many things that cause speciation a misrepresentation of what is currently known about the common molecular biology of species from microbes to man?
Nutrient chemicals and their metabolism to pheromones cause biologically based adaptive evolution. Two things in fact; not the many in theories.
Finkel, S. E., & Kolter, R. (2001). DNA as a Nutrient: Novel Role for Bacterial Competence Gene Homologs. J Bacteriol, 183(21), 6288-6293.
Kohl, J. V. (2012). Human pheromones and food odors: epigenetic influences on the socioaffective nature of evolved behaviors. Socioaffective Neuroscience & Psychology, 2, 17338 – DOI: 17310.13402/snp.v17332i17330.17338.
Nijland, R., & Burgess, J. G. (2010). Bacterial olfaction. Biotechnology Journal, 5(9), 974-977.
Palchevskiy, V., & Finkel, S. E. (2009). A Role for Single-Stranded Exonucleases in the Use of DNA as a Nutrient. J Bacteriol, 191(11), 3712-3716.
Shapiro, B. J., Friedman, J., Cordero, O. X., Preheim, S. P., Timberlake, S. C., SzabÃ³, G., et al. (2012). Population Genomics of Early Events in the Ecological Differentiation of Bacteria. Science, 336(6077), 48-51.