Attributes and Mysteries of Life: Symmetry, Twinning, Hemihypertrophy*, and Gynandromorphs; from the Archives of Neurology and Psychiatry, 1921
Comment: This interesting paper from the Archives of Neurobiology and Psychiatry brushes on several topics which are easily taken for granted; one of them is the symmetry of life. The article raises questions about the possibility of a single individual actually being a pair of twins. (There are cases of individuals called chimera who have two blood types and are considered to have been a pair of twins who fused.) The article also raises an interesting question about the differences and similarities between the process of bilateral symmetrical development, and twinning. This excerpt ends with the case of the beautiful bee that is a winged male on one side, and a wingless female on its other side. I doubt if modern medicine is any closer to discovering the enigma of the source of the symmetrical development of life. Probably, it is further than ever. (:
“‘By twinning we mean production of equivalent structures by division.’ This statement is taken from the biologist Bateson, who regards the power to divide as a fundamental attribute of life. The tendency to symmetry, to bilateral equivalence or mirror imaging is so general that it also must be regarded as a fundamental of biologic mechanics. Hemihypertrophy accordingly may be conceived as some profound inaccuracy in the natural process of developmental duplicity. It is not as monstrous as the double monster but it may have a related morphogenesis. At any rate, we can safely assume that hemihypertrophy is not an artifact really consisting in a hemi-atrophy. It is evidently a mild unilateral gigantism of an individual whose lesser somatic half is normal.
In a certain biologic sense we may regard every bilateral individual as being a pair of twins. H. H. Newman, in his fascinating work on the ‘Biology of Twins,’ holds that monozygotic twinning – where a single egg produces two offsprings – is a phenomenon that should be considered as only a phase of the much more general phenomenon of symmetrical division. The development of the right and left hand homologous organs in a bilateral organism is essentially a twinning process. This also observes that ‘the whole matter of bilateral development appears to be quantitative in nature, in that the same type of process may go not so far or farther than normal.’ Just as there may be an inhibition of the normal culmination of the process of bilateral division…so there is frequently an excess of division resulting in the two bilateral structures becoming completely segregated, as when a single individual develops two heads or two tails, while the remainder of the organism is a more or less normal individual. Newman, like Bateson, regards the phenomenon of twinning as a fundamental process which is almost universal in the field of biology.
From this point of view, hemihypertrophy may be interpreted as an atypical or imperfect form of twinning, a variant of the same process which may produce a double headed [creature] or a perfectly, ordinary normal individual – an ordinary individual being an organism in whom there has been a precisely balanced inhibition on the biologic process of bilateral doubling.
The actual mechanism of this regulative control over symmetry of size and form remains somewhat enigmatic in spite of much biologic investigation….
Newman has made suggestive researches into heredity and organic symmetry in armadillo quadruplets. He has noted some cases in which ‘one lateral half of the body has quite a different number of scutes from the other half, and one of these halves resembles the maternal condition.’ Since each set of quadruplets have the same genetic constitution as they arise from one zygote, he concludes that some irregularity in the mechanism of the mitotic cell-division is responsible for the anomalies of symmetry….
Another form of asymmetry, even more startling and drastic than hemihypertrophy is that of gynandromorphism. A gynandromorph is an animal that is male on one side and female on the other. This differentiation may include the reproductive organs, gonads and ducts. Usually it is longitudinally bilateral, but it may be anteroposterior.
This curious phenomenon is most frequent in insects but has been reported in birds and in a few mammals. A beautiful case was described in a mutillid wasp in which the male half of the body was black and winged like the male while the female half was rich red and wingless.”
*”Hemihypertrophy is a unilateral enlargement of one side of the body, and is one of the rarest among developmental anomalies.” Many people with this growth defect live happy and productive lives. Some undergo a surgery in the larger leg to inhibit its growth. It is more common that the right side is larger.