Musculoskeletal and Neural Comparison of Normal and Abnormal Development in Humans and Broader Medical Implications

Anatomical and medical studies of gross anatomical birth defects tend to focus mainly on external features, or in hard tissues (i.e., bones, cartilages, teeth). As a new, long term project we have been collecting and systematically comparing detailed musculoskeletal and neural information on normal human development and phenotypes seen in human fetuses, neonates and adults with conditions as diverse as anencephaly, trisomy 13, trisomy 18, trisomy 21, and/or cyclopia. This comparison is based on careful dissections and an extensive review of the scarce literature on the subject. Our dissections and comparisons revealed that certain similar anatomical patterns are frequently found in each of these conditions, supporting the “logic of monsters” hypothesis of Pere Alberch, according to which even in extreme cases of birth defects (e.g. anencephaly, cyclopia) there is still a discernable, marked “order”, instead of random, chaotic phenotypes, because of strong internal constraints limiting the amount of possible developmental outcomes. For instance, the absence of muscles that are normally polymorphic in humans (e.g., fibularis tertius, palmaris longus), the absence of tendons to the 5th digit of the hands/feet, and/or the presence of a few ‘atavistic’ muscles, are seen over and over in different cases of abnormal developmental studied by us. We will discuss the broader implications of our results and of the observed patterns by discussing crucial developmental and medical topics such as the links between developmental delay/arrest, ‘atavisms’, variations, anomalies, polymorphisms and the “logic of monsters”. Support or Funding Information Grants: This work is funded by start‐up funds to RD from Howard University College of Medicine, and by PhD funds from the Saudi Arabia government to MA.