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WILLIAM N. TAVOLGA
D. Evolution of Hearing
Probably one of the most primitive interactions between an organism
and its environment is one that is dependent upon physical contact. On
the multicellular level of organization, the specialization of contact
receptor cells appears to be one of the earliest to evolve. It is clear that
the specialization of an organ for reception of sound should be traceable
from primitive touch receptors with displacement-sensitive hairs. The
classic approach to the study of this evolutionary sequence is exemplified
in the review by Pumphrey ( 1950). The essentials of the sequence are:
free neuromasts that are groups of hair cells; the addition of a gelatinous
cupula and the organization of the neuromasts into more or less enclosed
lateral line organs; the development of otoconia and, later, otoliths that
mass-load the hair cells; and the enclosure of the hair cell groups within
the labyrinth. The functional sequence is : simple mechanoreceptors that
develop into more sensitive displacement detectors; enclosed mechanoreceptors become pressure sensitive as a result of the intervention of an
air-filled swim bladder; and in terrestrial vertebrates, the middle ear
takes on the coupling function of the swim bladder. According to
Pumphrey (1950), the response of the inner ear to gravity is “a byproduct of the improvement of hearing.”
Based upon a reexamination of the concepts of “sound and “hearing,”
van Bergeijk (1966, 1967a) presented an intensive survey of the problem
of the evolution of hearing in vertebrates and attempted to trace this
evolution in physiological terms. The lateral line organ is essentially a
displacement detector and, as a result, a hydrodynamic motion detector.
The organization of the lateral line system, however, provides new inputs
into the acoustic centers of the central nervous system, and the lateral
line system becomes a near-field hearing organ, with the capabilities of
localizing sound sources (van Bergeijk, 1964). By contrast with Pumphrey, van Bergeijk (1967a) proposed that the inner ear labyrinth arose
as an inertial receptor organ. Only the later development of a swim bladder ( a hydrostatic organ) gave the labyrinth the property of hearing. The
acoustic discontinuity of a swim bladder in an aquatic organism enables
it to respond to pressure waves, i.e., far-field sound, and the bladder
therefore generates a local near field that can excite the inner ear,
Specializations such as the Weberian apparatus improve the coupling of
the swim bladder and the inner ear and enhance far-field hearing. Van
Bergeijk carried this evolutionary sequence into the development of hearing in terrestrial vertebrates. His entire argument was brilliantly presented
and thoroughly documented, and it deserves recognition as a milestone
in the field of biology.
WILLIAM N. TAVOLGA
D. Evolution of Hearing
Probably one of the most primitive interactions between an organism
and its environment is one that is dependent upon physical contact. On
the multicellular level of organization, the specialization of contact
receptor cells appears to be one of the earliest to evolve. It is clear that
the specialization of an organ for reception of sound should be traceable
from primitive touch receptors with displacement-sensitive hairs. The
classic approach to the study of this evolutionary sequence is exemplified
in the review by Pumphrey ( 1950). The essentials of the sequence are:
free neuromasts that are groups of hair cells; the addition of a gelatinous
cupula and the organization of the neuromasts into more or less enclosed
lateral line organs; the development of otoconia and, later, otoliths that
mass-load the hair cells; and the enclosure of the hair cell groups within
the labyrinth. The functional sequence is : simple mechanoreceptors that
develop into more sensitive displacement detectors; enclosed mechanoreceptors become pressure sensitive as a result of the intervention of an
air-filled swim bladder; and in terrestrial vertebrates, the middle ear
takes on the coupling function of the swim bladder. According to
Pumphrey (1950), the response of the inner ear to gravity is “a byproduct of the improvement of hearing.”
Based upon a reexamination of the concepts of “sound and “hearing,”
van Bergeijk (1966, 1967a) presented an intensive survey of the problem
of the evolution of hearing in vertebrates and attempted to trace this
evolution in physiological terms. The lateral line organ is essentially a
displacement detector and, as a result, a hydrodynamic motion detector.
The organization of the lateral line system, however, provides new inputs
into the acoustic centers of the central nervous system, and the lateral
line system becomes a near-field hearing organ, with the capabilities of
localizing sound sources (van Bergeijk, 1964). By contrast with Pumphrey, van Bergeijk (1967a) proposed that the inner ear labyrinth arose
as an inertial receptor organ. Only the later development of a swim bladder ( a hydrostatic organ) gave the labyrinth the property of hearing. The
acoustic discontinuity of a swim bladder in an aquatic organism enables
it to respond to pressure waves, i.e., far-field sound, and the bladder
therefore generates a local near field that can excite the inner ear,
Specializations such as the Weberian apparatus improve the coupling of
the swim bladder and the inner ear and enhance far-field hearing. Van
Bergeijk carried this evolutionary sequence into the development of hearing in terrestrial vertebrates. His entire argument was brilliantly presented
and thoroughly documented, and it deserves recognition as a milestone
in the field of biology.