I think this discussion might benefit from everyone specifying the units of evolution they are referring to when they talk about evolutionary process. RazD has made reference to this, but many other references to evolutionary processes do not specify the units under discussion or distinguish between genes, individuals, or species and this is important.
The gene is a unit of inheritance, not a unit of selection. The lowest level at which selection can act is on the individual. This is also the level at which selective forces are strongest. Selection in some forms can sometimes act at higher levels (groups), but discussions about species evolution often erroneously imply that selection acts on species - it doesn't. Species, as gene pools, are units of evolution, but they are not units of selection. Similarly, adaptations are a property of populations or species, not individuals. A species' fate (persistence, divergence into many other species, or extinction) is some function of its genetic potential, inherent biological constraints determined by its phylogeny, and chance events, all played out in the context of a changing environment. Species can evolve/adapt quickly under some circumstances, slowly under others, or remain virtually unchanged for millenia. Thus biological complexity is one possible outcome of species evolution, but it is not an inevitable result.
This message has been edited by EZscience, 03-21-2006 09:14 AM
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