Hall Brian K
Department of Biology, Dalhousie University, Halifax, NS B3H 4J1, Canada.
J Hum Evol. 2007 May;52(5):473-9. doi: 10.1016/j.jhevol.2006.11.010. Epub 2007 Feb 20.
Homology is the presence of the same feature in two organisms whose most recent common ancestor also possessed the feature. I discuss the bases on which we can tell that two features being compared share sufficient elements of sameness to allow them to be treated as homologous and therefore to be legitimately compared with one another in a way that informs comparative, evolutionary, and phylogenetic analysis. To do so, I discuss the relationship(s) between homology and homoplasy to conclude that we are dealing neither with a dichotomy between homoplasy as parallelism/convergence and homology as common descent nor with a dichotomy of homoplasy as the interrupted presence of the character in a lineage and homology as the continuous presence of the character. Rather, we are dealing with common descent with varying degrees of modification. Homoplasy and homology are not dichotomies but the extremes of a continuum, reflecting deep or more recent shared ancestry based on shared cellular mechanisms and processes and shared genes and gene pathways and networks. The same genes can be used to initiate the development of homoplastic and homologous structures. Consequently, structures may be lost but their developmental bases retained, providing the potential for homoplasy. It should not be surprising that similar features persist when a feature is present in the nearest common ancestor (homology). Neither should it be surprising to find that different environments or selective pressures can trigger the reappearance of similar features in organisms that do not share a recent common ancestor (homoplasy).
同源性是指在两个生物体中存在相同的特征,而它们最近的共同祖先也拥有该特征。我将讨论我们能够判断所比较的两个特征具有足够的相同元素,从而可将它们视为同源特征,并因此能够以一种有助于比较、进化和系统发育分析的方式进行合理比较的依据。为此,我将讨论同源性和同功性之间的关系,以得出这样的结论:我们既不是在处理同功性(作为平行/趋同)与同源性(作为共同祖先)之间的二分法,也不是在处理同功性(作为特征在一个谱系中的间断出现)与同源性(作为特征的连续出现)之间的二分法。相反,我们处理的是具有不同程度修饰的共同祖先。同功性和同源性不是二分法,而是一个连续体的两端,反映了基于共享细胞机制和过程以及共享基因、基因途径和网络的深度或更近的共同祖先。相同的基因可用于启动同功和同源结构的发育。因此,结构可能会丢失,但它们的发育基础会保留下来,从而提供了同功性的可能性。当一个特征存在于最近的共同祖先中时(同源性),相似的特征持续存在并不奇怪。在没有最近共同祖先的生物体中,不同的环境或选择压力会触发相似特征的再次出现(同功性),这也不足为奇。