Field homology: a meaningful definition.
Field homology refers to populations of cells that derive from evolutionarily conserved regions of embryos but are distributed across sets of adult morphological structures that cannot be placed in one-to-one correspondance. The concept of field homology has proven especially attractive to comparative neurologists because it allows them to deal with the fact that sets of nuclei or nuclear subdivisions often cannot be compared on a one-to-one basis across phyletic groups. However, the concept of field homology has recently come under criticism. It has been argued that field homology is theoretically impossible because it requires sequences of developmental stages to be both evolutionarily conserved and evolutionarily modified. It has also been argued that field homology allows overly vague comparisons of adult morphological structures, fails to account for homologous structures that derive from non-homologous embryonic sources, and establishes overly rigid links between embryonic and adult morphology. All of these criticisms may be adequately addressed by explaining field homology in terms of differentiation. The present paper explains field homology in terms of differentiation using the amniote dorsal thalamus to illustrate major points. It is concluded that field homology is a meaningful concept when defined in terms of differentiation, applied to appropriate cases, and properly limited in its comparisons of adult structures.
Krasnow Institute for Advanced Study, George Mason University, Fairfax, VA 22030-4444, USA. kcookson@gmu.edu
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D000818:Animals; D005075:Biological Evolution; D002454:Cell Differentiation / Q000502:physiology; D004622:Embryo, Mammalian / Q000502:physiology*; D004625:Embryo, Nonmammalian; D005314:Embryonic and Fetal Development; D008954:Models, Biological; D009024:Morphogenesis; D009474:Neurons / Q000166:cytology; D013788:Thalamus / Q000166:cytology / Q000196:embryology