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Skeletal Biology

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The article is; A Model For Development And Evolution Of Complex Morphological Structures. Published in 1991, the authors are;

ATCHLEY, W. R – He was the head of Department of Genetics, North Carolina State University, Raleigh, NC 27695-7614

HALL, B. K.- He was in the Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1

The purpose of the article is to show the complex morphological structure of a mammal, how it develops and changes with time due to evolution and the factor of adaptation for better survival. The model is based on the premise that structural changes in the mammalian craniomandibular region is due to the act of natural selection that increases the strong and well adaptable features. Natural selection refines the process of integration of the various morphogenetic components in order for an organism to adapt to the different environmental changes that have occurred over time. The article focuses on the changes that have occurred on the skeletal and bone structure of mammals as far back as anthropology can proof.

The aim of the article is to establish that the morphological changes in the structure and functioning were due to several genetic and epigenetic factors. In order to establish the changes in which the current mammals change in their morphology, an embryo was closely examined in order to establish the developmental changes that occur in the organism before it achieves the final skeletal structure. The article addresses the development units; in this case the development units are the cellular condensation characteristics that are produced in the embryonic stage of the crest cells.

The methodology involved the use of the following as the items to be considered; the number of cell in the preskeletal condensation (n), the cell diffusion rate (r), the cell death rate (d), and the fraction of cells that is mitotically active during the condensation (f). The development units are analyzed in terms of the tissue differentiation process that they undergo. These includes; osteogenesis, chondrogenesis and endochondralossification.

In order to determine the changes and at exactly what stage they occurred the influence of the following factors on the development units is established. The factors are;

The cell lineage that the cell arises from

Inductive tissue interaction

The cell differentiation regulation

Extrinsic factors for instance hormones and muscles

According to the article, it was established that differences in mandibular morphology is not just affected by inheritable factors, but it is also subject to the process of natural selection. The divergent differences among organisms have occurred through changes in the above mentioned development units (Richards, 1988).

The difference in skeletal make up of organisms is subject to both nature and nurture and the effects of both factors, has demonstrated diversity. At the same time natural selection is meant to increases changes of survival for the mammals (Jantz, 1981). This is the reason as to why the changes analyzed from the above model from the embryo stage of the mammal to the point where the skeletal is fully developed. All the changes are meant to increase efficiency of the structure in the functioning of the organism.

The article explains the effects of developmental and evolutionary changes on the morphological structure and functioning of a mammal. Based on proper scientific observation, analysis and evidence; the model proofs that indeed the changes that occur to the mammals are still occurring due to genetic and environmental issues. The model also explains the relationship between the cell differentiation process and the skeletal structure.


Atchley, W. R. Hall, B. K. (1991). A Model for Development and Evolution of Complex Morphological Structures. Biological Reviews, 66: 101–157. doi: 10.1111/j.1469-185X.1991.tb01138.x, Issue published online: 21 JAN 2008Article first published online: 21 JAN 2008.

Jantz, L. R. Ubelaker, H. D. (1981). Progress in Skeletal Biology of Plains Population, Cambridge University Press, London

Richards, D. G. (1988). Human Skeletal Biology: Contribution to the Understanding of the Skeletal Structure, Orthodox Print Press, New York

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