American Journal of Plant Sciences, 2013, 4, 1998-2000
http://dx.doi.org/10.4236/ajps.2013.410248 Published Online October 2013 (http://www.scirp.org/journal/ajps)
On the Origin of the Common Bean (Phaseolus vulgaris L.)
Andrés J. Cortés1,2
1Departamento de Biologia, Universidad de los Andes, Bogotá, Colombia; 2Department of Plant Ecology and Evolution, Evolution-
ary Biology Centre, Uppsala University, Norbyvägen 18D, Uppsala, Sweden.
Email: andres.cortes@ebc.uu.se
Received June 8th, 2013; revised July 9th, 2013; accepted August 1st, 2013
Copyright © 2013 Andrés J. Cortés. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Phylogeographic methods provide the tools to accurately access the geographic origin and diversification of crop spe-
cies. In the present commentary, I urge the common bean community to face those methods and a tree-thinking mental-
ity with regards to the long standing debate of th e origin of common bean. Such efforts will ultimately bring back inter-
est into wild bean studies and reinforce th e uniquen ess of this species as a system to study diversification , domesticatio n
and adaptive processes across the two most diverse hotspots in the world.
Keywords: Phylogeography; Domestication; Bottlenecks; Outgroups; Andes; Mesoamerica
1. Introduction
Wild bean is thought to have diversified in South and
Central America, after which domestication in the south-
ern and northern ends of each region gave independent
origin to the Andean and Mesoamerican domesticates.
Additional structure within each of these genepools ac-
counts for up to 10 different races. Both genepools fol-
lowed parallel pathways of dissemination through the
world, generating new secondary centers of diversity in
Africa and Asia [1].
Several recent works defended a Mesoamerican origin
of the common bean [2,3]. This was mainly based on the
extensive diversity and population structure within the
Mesoamerican genepool, and the signature of predomes-
tication bottlenecks in the south of the Andes detected in
5 genes across 102 wild accessions. However, these two
main lines of evidence are not on ly circumstantial, bu t do
not exclude an Andean origin of common bean. Exten-
sive population structure does not necessarily correlate
with origin, and may also be the result of widespread lo-
cal adaptation and unparalleled genetic drift across the
Mexican and Guatemalan valleys [1,4]. Meanwhile, de-
mographic bottlenecks in the south of the Andes may
have occurred during colonization either from Mesoa-
merica or from Ecuador and North Peru, and therefore do
not exclude the possibility that the origin of common
bean is in the latter region with the absence of strong bot-
tle-necks during the north ern radiation.
Several arguments against a phenetic approach, as the
one that has been repeatedly applied to address the origin
of beans, must also be considered. In the first place, there
are no living ancestral populations or lineages because each
one has had the same period of quasi-independent evolu-
tion since divergence [5]. Therefore, in the absence of
outgroups it is not possible to reconstruct ancestral char-
acter states and areas. It will only be possible to identify
ancestral alleles, and to differentiate the two competitive
hypotheses regarding the origin of common bean if the
previous surveys had been combined with a set of care-
fully chosen Phaseolus species (Figure 1). This would pro-
vide a rooted cladogram and an appropriate phylogenetic
inference. Nowadays, wild bean s are still bein g discover-
ed [6] and further expeditions in the west slopes of the
Ecuadorian and Northern and Central Peruvian Andes are
urgently required. A clearer picture of the distribution of
the wild accessions is ess ential to carry out a n accurate re-
construction of ancestral areas. Furthermore, archeologi-
cal clues are much older in the Andes than in Mesoame-
rica, and therefore its inclusion is crucial for an accurate
reconstruction of areas. Secondly, the genetic proximity
between some accessions from the south of the Andes and
some from central Mexico may not be due to incomplete
linage sorting of ancestral polymorphism, but instead to
homoplasy or ancestral introgression [7]. The first option
seems particularly plausible in the previous works be-
cause they did not use character-state tree reconstruction
methods, but distance methods; even though the former
methods are the ones that incorporate the nucleotide mu-
tation processes into the phylog enetic inference [8].
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