Hox genes play an important role in the specification of the primary body axis [ 56] as well as in later ontogenetic processes demanding highly specific regulation such as limb development [ 57].
This fact indicates that MuERV still possesses the capability to overcome cell membranes during embryogenesis and predisposes one to believe that ERVs might play a general role in signal transduction pathways and thus for coordination and regulation of ontogenetic processes in frogs and probably also in other vertebrates.
In the light of this consideration, the timing of development of FPR has an important role in the ontogenetic process of infants.
A wide range of variation in human craniofacial form exists and can be relatively easily altered through minor shifts in the ontogenetic process [ 9].
Variation in AOC may also reflect early ontogenetic processes caused by maternal effects [54] [56].
Concurrent appraisal of the ontogenetic processes producing variation in intestinal length, and the functional significance of these processes (i.e., associations with diet) in a phylogenetic context is similarly lacking.
An important question concerns the epigenetic mechanisms by which species differences in brain architecture arise during ontogeny, in particular the relative roles of early, genetically guided ontogenetic processes versus later processes influenced substantially by environmental input and/or hormones.
Nonetheless, since the cranium starts to develop before birth [ 16– 18] and continues to develop until adulthood, it is fundamental to understand the ontogenetic processes, including a comparison of these processes in diverse groups of humans.
In terms of environmental contamination, these studies show that attention to ontogenetic processes, genetic background, developmental stage, timing and duration of exposure, and the interactions associated with mixtures is critical to quality risk assessment.
In addition to conceptual work on the biological bases of homology, variation, and parallel evolution, my research has focused on evolutionary changes in size and shape in mammals: the functional consequences of these changes, and the evolutionary modifications of ontogenetic processes that produce them.
