Research ArticleEVOLUTIONARY BIOLOGY

A universal scaling law of mammalian touch

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Science Advances  09 Oct 2020:
Vol. 6, no. 41, eabb6912
DOI: 10.1126/sciadv.abb6912
  • Fig. 1 Schematic of our skin model (layer thicknesses not to scale), showing the DPC.

    Layers are numbered as in the governing equations.

  • Fig. 2 Decay of skin waves.

    The amplitude (relative to P-wave amplitude at 5 cm) of all three permissible wave types as a function of distance from a sphere of radius 8 mm oscillating normal to the skin at a frequency of 200 Hz, showing a relatively slow decay of the Rayleigh wave (section S6).

  • Fig. 3 Wave interaction with the PCs.

    (A) Schematic of our model of the PCs (full details in the Supplementary Materials). (B) Example of excitation modes for a PC. (C) Filtering of the P-wave excitation modes by the structure of the PC, showing that the dominant mode 0 is filtered out. (D) Rayleigh and S-wave amplitudes transmitted to the core of the Pacinian, relative to P-waves, for a range of frequencies, showing the dominance of the Rayleigh wave signal.

  • Fig. 4 Properties of skin Rayleigh waves are insensitive to hydration levels.

    As the stiffness of the stratum corneum (SC), a proxy for hydration levels, varies, the wavelength of the P- and S-waves changes considerably, while the Rayleigh wave remains largely unaffected. Range of Young’s moduli was taken from experimental data (2). Location of the body is the forearm data and a frequency of 200 Hz.

  • Fig. 5 Across a range of mammals of varying sizes, including aquatic and semiaquatic species, but excluding rodents, the ratio of the skin Rayleigh wavelength to the DPC is evolutionarily conserved, with an approximate value of 5/2.

    Note that the hypervasculated skin of the giraffe is not incorporated in our model, and hence, the giraffe lies slightly off the trend line. Source of data (3243).

Supplementary Materials

  • Supplementary Materials

    A universal scaling law of mammalian touch

    J. W. Andrews, M. J. Adams, T. D. Montenegro-Johnson

    Download Supplement

    This PDF file includes:

    • Sections S1 to S8
    • Figs. S1 to S5
    • Tables S1 to S7
    • References

    Files in this Data Supplement:

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