Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Stiffness of the human foot and evolution of the transverse arch   Foot stiffness underlies its mechanical function, and is central to the
evolution of human bipedal locomotion. The stiff and propulsive human foot has
two distinct arches, the longitudinal and transverse. By contrast, the feet of
non-human primates are flat and softer. Current understanding of foot stiffness
is based on studies that focus solely on the longitudinal arch, and little is
known about the mechanical function of the transverse arch. However, common
experience suggests that transverse curvature dominates the stiffness; a
drooping dollar bill stiffens significantly upon curling it along the
transverse direction, not the longitudinal. We derive a normalized curvature
parameter that encapsulates the geometric principle underlying the transverse
curvature-induced stiffness. We show that the transverse arch accounts for
almost all the difference in stiffness between human and monkey feet (vervet
monkeys and pig-tailed macaques) by comparing transverse curvature-based
predictions against published data on foot stiffness. Using this functional
interpretation of the transverse arch, we trace the evolution of hominin feet
and show that a human-like stiff foot likely predates Homo by $\sim 1.5$
million years, and appears in the $\sim 3.4$ million year old fossil from
Burtele. A distinctly human-like transverse arch is also present in early
members of Homo, including Homo naledi, Homo habilis, and Homo erectus.
However, the $\sim 3.2$ million year old Australopithecus afarensis is
estimated to have possessed a transitional foot, softer than humans and stiffer
than other extant primates. A foot with human-like stiffness probably evolved
around the same time as other lower limb adaptations for regular bipedality,
and well before the emergence of Homo, the longitudinal arch, and other
adaptations for endurance running.

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The categories of this paper are: stat
34
The categories of this paper are: chem-ph
25
The categories of this paper are: patt-sol
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
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The categories of this paper are: nucl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
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The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
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The categories of this paper are: acc-phys
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The categories of this paper are: chao-dyn
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The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc