June 14, 2006 | David F. Coppedge

More Darwinian Assumptions Shot Down

Here are two articles that appear to kick out some once-solid props from evolutionary theory.  Readers are encouraged to get the details from the original papers, listed in the footnotes.

  • Environmental Impotence:  Many evolutionists have claimed that the environment produces strong selection effects.  Indeed, the fitness landscape itself evolves, carrying with it the constraints driving animals and plants to adapt or perish.  A new paper in PLoS Biology1 casts doubt on this assumption.  Wilson et al. examined environmental effects on wild sheep.  The team studied, “for the first time, how variation in environmental quality simultaneously influences the strength of natural selection and the genetic basis of trait variability.”  Unfortunately, the results were opposite than expected: “our results show that environmental heterogeneity induces a negative correlation between these two parameters.”  The implications seem damaging for evolutionary theory in general:

Harsh environmental conditions were associated with strong selection for increased birthweight but low genetic variance, and vice versa.  Consequently, the potential for microevolution in this population is constrained by either a lack of heritable variation (in poor environments) or by a reduced strength of selection (in good environments).  More generally, environmental dependence of this nature may act to limit rates of evolution, maintain genetic variance, and favour phenotypic stasis in many natural systems.  Assumptions of environmental constancy are likely to be violated in natural systems, and failure to acknowledge this may generate highly misleading expectations for phenotypic microevolution.

  • Birds Can’t Tell Molecular Time:  Evolutionists used to think the molecular clock was steady.  That assumption has taken another blow in Molecular Genetics and Evolution.2  The authors began, “Current understanding of the diversification of birds is hindered by their incomplete fossil record, and uncertainty in phylogenetic relationships and phylogenetic rates of molecular evolution.”  So they decided to study the phylogenetic rates of molecular evolution.  Did it help?  “We found no support for the hypothesis that the molecular clock in birds ‘ticks’ according to a constant rate of substitution per unit of mass-specific metabolic energy rather than per unit of time, as recently suggested.”  Did they offer a solution?  Not exactly; but this realization “will therefore aid comparative biology studies that seek to infer the origin and timing of major adaptive shifts in vertebrates.”  In other words, the bad news is not just for the birds.

1Wilson et al., “Environmental Coupling of Selection and Heritability Limits Evolution,” Public Library of Science Biology, Volume 4 | Issue 7 | July 2006.
2Pereira and Baker, “A Mitogenomics Timescale for Birds Detects Variable Phylogenetic Rates of Molecular Evolution and Refutes the Standard Molecular Clock,” Molecular Biology and Evolution, Advance Access published online on June 14, 2006 Molecular Biology and Evolution, doi:10.1093/molbev/msl038.

We thank some readers for bringing these two papers to our attention.  The closer you examine each evolutionary claim, the weaker it looks.  How many other assumptions underlying the “fact” of evolution are rotting away?

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Categories: Birds, Genetics

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