A Neglected Dimension of Evolution and the Origin of Species
Some of Darwins crucial views and ideas have been refuted by his followers in the 20th century.In this essay,I will first discuss how one of the centerpieces of Darwins theory,the Principle of Divergence,a theory in which Darwin himself expressed very great confidence,fared in the last century.I will then argue for the importance of linkage,a prominent factor of evolution that has been largely neglected in modern evolutionary theory.I propose that there is now sufficient evidence suggesting that linkage should be added to the list of evolutionary forces.This essential and general yet longneglected factor constitutes an intrinsic isolating mechanism of evolution (referred to as ‘genealogical isolation),constituting a key principle for understanding speciation andthe inevitable discontinuities of life forms in the hierarchical biological system.Moreover,linkage can form a theoretical mechanism for Darwins Principle of Divergence.Multiple genetic variations in gene(s) that are strongly linked can be inherited as a single unit along genealogical lineages,a phenomenon referred to as the ‘block transmission of genetic variation.A greater understanding of this characteristic of variation and inheritance may shed light on several puzzles currently facing evolutionary biologists.First,block transmission suggests that gaps among species are the inevitable results of evolution stemming from within-species divergence; therefore,the lack of immediate transitional forms would be expected as largely natural and not entirely due to the incompleteness of the fossil record.Second,geographical isolation is not a prerequisite for speciation since genealogical isolation,despite interbreeding,is inevitable.Consequently,the primary obstacle to sympatric speciation disappears.Third,any gene,if obtaining a selective advantage following accumulation of mutations,can act as a speciation gene,if it is physically or functionally linked to another gene,which subsequently builds up mutation(s) leading to incompatibility.Thus,universal speciation gene does not exist.Reproductive isolation is a by-product of evolution due to mutations causing incompatibility either physiologically,ecologically or behaviorally.Fourth,the presence of extensive genetic polymorphism in natural populations may be due to various levels of buffering effects that offset the deleterious nature of mutations.This makes many mutations appear effectively neutral,or nearly neutral.Therefore,most mutations are probably not predetermined at birth to have an inherent nature that is neutral,beneficial or deleterious.Rather,their nature largely depends on their context,defined by genetic background,physiological states,ecological conditions,and other variables.The deductions outlined in this essay are rather preliminary.However,our hypotheses are falsifiable since they allow many predictions to be made,and,importantly,they are consequently amenable to rigorous testing.
Haplotype block linkage reproductive isolation species concept sympatric speciation
De-Xing Zhang
Center for Computational and Evolutionary Biology,and State Key Laboratory of Integrated Management of Pest Insects and Rodents,Institute of Zoology,Chinese Academy of Sciences,Beijing 100101,China
国际会议
The Darwin 200 Beijing International Conference (纪念达尔文诞辰200周年国际学术会议)
北京
英文
286-303
2009-10-24（万方平台首次上网日期，不代表论文的发表时间）