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This makes sense. If a species is thriving and not under much selective pressure, it does not have to be optimized for its environment to survive. This allows

This makes sense. If a species is thriving and not under much selective pressure, it does not have to be optimized for its environment to survive. This allows for a larger amount of genetic variance. Most mutations either are maladaptions, don't cause any significant change or lead to death while relatively few confer an advantage. In addition, some adaptations may take many generations of mutation to actually provide an advantage or may need time to find a niche where a mutation that is a maladaptation in one environment may be an advantage in others (Sickle cell anemia gives resistance to malaria, Tay Sachs does the same for tuberculosis). When selective pressures/shocks arise, there is a wider amount of genetic variance that can adapt to the new environment... a larger menu of options for survival, and this pressure acts as a feedback loop, further promoting that more mutations in that direction. Think of the pressures that led to the growth of the giraffe's neck. Perhaps it is this combination... allowing time for a species to thrive and have genetic diversity and shocks which select for and promote the evolutionary path

GedByrne 9y ago
Does genetic variation rise in response to selective pressure? It seems to me that this is a two stage process. 1. Variation is introduced at a fairly constant rate by mutation. 2. Variation is filtered out by natural selection based on how well it fits the environment. The shocks occur when the environment changes so that the criteria for fit change and new variations survive for the long term. So when we look at evolution we see a rate of change driven by the rate of mutation. When we look at the long term we see a rate of change driven by the environment.
- FullMtlAlcoholc 9y ago
  I agree. When I look at the long term though, the environment and mutation are just different parts of the same whole. Both are necessary for phenotypic changes and speciation. Even that is simplistic. It doesn't take into account the significance of viral transfer of dna and other epigenetic factors, how an environment can cause normally dormant genes to express themselves, sexual selection where attractiveness != most environmentally fit, etc.

GedByrne 9y ago

Does genetic variation rise in response to selective pressure? It seems to me that this is a two stage process. 1. Variation is introduced at a fairly constant rate by mutation. 2. Variation is filtered out by natural selection based on how well it fits the environment. The shocks occur when the environment changes so that the criteria for fit change and new variations survive for the long term. So when we look at evolution we see a rate of change driven by the rate of mutation. When we look at the long term we see a rate of change driven by the environment.

FullMtlAlcoholc 9y ago
I agree. When I look at the long term though, the environment and mutation are just different parts of the same whole. Both are necessary for phenotypic changes and speciation. Even that is simplistic. It doesn't take into account the significance of viral transfer of dna and other epigenetic factors, how an environment can cause normally dormant genes to express themselves, sexual selection where attractiveness != most environmentally fit, etc.