A MODEL FOR DEVELOPMENT AND EVOLUTION OF COMPLEX MORPHOLOGICAL STRUCTURES

摘要: How 'complex' or composite morphological structures like the mammalian craniomandibular region arise during development and how they are altered evolution two major unresolved questions in biology. Herein, we have described a model for of complex structures. The assumes that natural selection acts upon an array phenotypes generated by variation variety underlying genetic epigenetic controlling factors. Selection refines integration various morphogenetic components ontogeny order to produce functioning structure adapt organisms differing patterns environmental heterogeneity. was applied mandible (which is used as paradigm structures). embryology examined detail identify fundamental developmental units which necessary assemble final structure. quite general since equivalent exist many other biological This could be developing well groups organisms. For example, it can cell parameters Drosophila (Atchley, 1987). discussed this paper changes result from evolutionary its units. relate characteristics cellular condensations produced differentiation embryonic neural crest cells. include: number stem cells preskeletal (n), time initiation condensation formation (t), fraction mitotically active within (f), rate division these (r), their death (d). These derivative terms types tissue (chondrogenesis, osteogenesis, primary/secondary intramembranous/endochondral ossification) growth properties regions mandible. Variation five provides basis ontogenetic phylogenetic modification mandibular morphology. We influenced (a) lineage arise, (b) epithelial-mesenchymal (inductive tissue) interactions, (c) regulation differentiation, (d) extrinsic factors such muscles, teeth hormones. Evidence provided morphology heritable, subject selection, divergence among different stocks has apparently occurred through structures.(ABSTRACT TRUNCATED AT 400 WORDS)