Part I: Evolution, Taxonomy, and Domestication40
have significantly improved our understanding of domestica-
tion and breed formation (i.e. Larson et al. 2005, 2007a; Megens
et al. 2008; Groenen et al. 2012; Rubin et al. 2012; Frantz et al.
2013; Bosse et al. 2014), relatively little is known, in comparison,
about the concomitant morphological changes that we know
occurred.
The study of morphological changes associated with domes-
tication has interested the scientific community for a long
time. The pioneering work in this area dates back to Darwin
in 1868 with the publication of his book The variation of ani
mals and plants under domestication (Darwin 1868). A classical
approach to study the domestication process is to compare wild
and domestic modern forms of the same species, assuming that
the current wild populations accurately reflect their ancestral
wild counterparts (Price 2002). However, many intermediates
exist, or have existed, such as hybrid populations, feral (domes-
tic returned to a wild state) or captive wild boar, which are the
result of complex interactions between natural and artificial
selection pressures. Since Darwin, morphological changes
associated with domestication have been shown to involve a
reduction in brain and body size, changes in the proportions
of body parts, changes in external features such as new colora-
tions, wavy or curly hair, shorter and coiled tails and floppy
ears (e.g. O’Regan & Kitchener 2005; Dobney & Larson 2006).
A decrease in size during animal domestication has been dem-
onstrated in many species such as dogs, cows, sheep, goats, and
pigs (e.g. Davis 1981; Peters et al. 1999; Albarella et al. 2005;
Zeder 2006; Hongo et al. 2009). Traditional linear measure-
ments of the size of modern and ancient teeth and bones are
often used to identify the wild or domestic status of animals in
the archaeological record (Vigne et al. 2005). More generally,
size reduction through time is recognized as one of the first
indicators of domestication in the past (e.g. Boessneck & Von
Den Driesch 1978; Meadow 1989). However, these morpho-
logical changes induced by human selective pressure remain
questionable for investigating the early stages of the process
itself (Arbuckle 2006) and further investigation of the plastic
response to environmental stress induced by the domestication
process is required in order to decipher the earliest part of that
process.
The development of geometric morphometric approaches
(Bookstein 1991; Rohlf & Marcus 1993) has vastly improved
morphometric studies dealing with the morphological changes
linked with domestication (Cucchi et al. 2011b; Evin et al. 2013).
The main advance over so-called ‘traditional morphometrics’ is
that biological forms are no longer captured by sets of independ-
ent linear measurements of length or angles, but by sets of point
coordinates, drastically improving the capture of the geometric
complexity of form. The coordinates of points can be measured
in two or three dimensions depending on the object studied
(e.g. 2D for teeth and 3D for skulls). Curves and outlines in 2D
can be analysed with an Elliptic Fourier Transform (Kuhl and
Giardina, 1982) (Figure 4.1). The set of coordinates from 2D and
3D landmarks or from 2D and 3D curves and surfaces can also
be made comparable by a Procrustes superimposition follow-
ing three steps (Figure 4.2): superimposition of the centroids
of the objects, normalization by size, and rotation. During thenormalization step, the size used is called the ‘centroid size’ and
is a measure of the dispersion of the points around the centroid
of the object. The new coordinates obtained after superimposi-
tion correspond to the shape of the object. This procedure has
the advantage of more efficiently separating size and shape. The
allometries, corresponding to the changes in shape associated
with changes in size, can also be explored. Geometric morpho-
metrics is commonly used in biology, but (until recently) rarely
in archaeology. The few archaeozoological and archaeobotani-
cal studies using these techniques involve the study of disper-
sal and migration (e.g. Larson et al. 2007b; Cucchi et al. 2013;
Ottoni et al. 2013; Newton et al. 2014), taxonomic identification
of archaeological remains (e.g. Cucchi et al. 2009, 2011b; Terral
et al. 2010; Burger et al. 2011; Evin et al. 2013; Krause-Kyora
et al. 2013; Stoetzel et al. 2013; Pagnoux et al. 2014; Ros et al.
2014; Cornette et al. 2015), the study of commensalism (Cucchi
et al. 2011a, 2013; Valenzuela-Lamas et al. 2011), domestication
(e.g. Terral et al. 2004; Cucchi et al. 2011b; Owen et al. 2014;
Evin et al. 2015a, 2015b) and anthropogenic insular evolution
(Cucchi et al. 2014).
So far, at least 14 publications that include geometric mor-
phometric data of modern and/or archaeological domestic pigs
can be listed (until January 2016, Figure 4.3, Table 4.1).
We assessed the morphometric variation of wild and domes-
tic pigs using two main kinds of data: two-dimensional analyses
of the occlusal view of upper and lower molar teeth (M2 and M3
specifically), and three-dimensional analyses of whole or partial
crania. The studies analysed teeth using landmark and sliding
semi-landmark based approaches (Figure 4.2) as well as outline
analyses using elliptic Fourier transforms (Figure 4.1). Crania
were analysed using 3D landmarks.
We performed geometric morphometric analyses for three
main purposes: (1) the identification of domestic pigs in archae-
ological records, (2) the study of human-mediated dispersals,
and (3) a better understanding of the evolutionary processes
that led to the domestic phenotypes.Domestication and Phenotypic Change in
Modern Pigs
Several articles describe the differences between modern, wild
and domestic pigs (Cucchi et al. 2009; Cucchi et al. 2011b; Evin
et al. 2013, 2015a; Owen et al. 2014), but only two studies include
more categories than the simple dichotomous wild and domes-
tic forms – i.e. feral, hybrids, and captive wild boar (Owen et al.
2014; Evin et al. 2015a).
Domestication has induced drastic morphological changes
in most species, and pigs are no exception. Pigs were primarily
selected for meat production (Vigne 1998; Pond & Mersmann
2001; Rehfeldt et al. 2008) and it is very unlikely that pigs were
selected based on their tooth morphology. However, because tooth
and skull variations have high heritability (Caumul & Polly 2005),
their morphologies do reflect the past history of selection.
Understanding the evolutionary processes underpinning
the morphological changes observed between modern popula-
tions allows improved interpretation of how humans have been
able to shape species over time to meet their needs..00612:31:36