981 research outputs found
Inferring processes of cultural transmission: the critical role of rare variants in distinguishing neutrality from novelty biases
Neutral evolution assumes that there are no selective forces distinguishing
different variants in a population. Despite this striking assumption, many
recent studies have sought to assess whether neutrality can provide a good
description of different episodes of cultural change. One approach has been to
test whether neutral predictions are consistent with observed progeny
distributions, recording the number of variants that have produced a given
number of new instances within a specified time interval: a classic example is
the distribution of baby names. Using an overlapping generations model we show
that these distributions consist of two phases: a power law phase with a
constant exponent of -3/2, followed by an exponential cut-off for variants with
very large numbers of progeny. Maximum likelihood estimations of the model
parameters provide a direct way to establish whether observed empirical
patterns are consistent with neutral evolution. We apply our approach to a
complete data set of baby names from Australia. Crucially we show that analyses
based on only the most popular variants, as is often the case in studies of
cultural evolution, can provide misleading evidence for underlying transmission
hypotheses. While neutrality provides a plausible description of progeny
distributions of abundant variants, rare variants deviate from neutrality.
Further, we develop a simulation framework that allows for the detection of
alternative cultural transmission processes. We show that anti-novelty bias is
able to replicate the complete progeny distribution of the Australian data set
Translucent windows: How uncertainty in competitive interactions impacts detection of community pattern
Trait variation and similarity among coexisting species can provide a window
into the mechanisms that maintain their coexistence. Recent theoretical
explorations suggest that competitive interactions will lead to groups, or
clusters, of species with similar traits. However, theoretical predictions
typically assume complete knowledge of the map between competition and measured
traits. These assumptions limit the plausible application of these patterns for
inferring competitive interactions in nature. Here we relax these restrictions
and find that the clustering pattern is robust to contributions of unknown or
unobserved niche axes. However, it may not be visible unless measured traits
are close proxies for niche strategies. We conclude that patterns along single
niche axes may reveal properties of interspecific competition in nature, but
detecting these patterns requires natural history expertise firmly tying traits
to niches.Comment: Main text: 18 pages, 6 figures. Appendices: A-G, 6 supplementary
figures. This is the peer reviewed version of the article of the same title
which has been accepted for publication at Ecology Letters. This article may
be used for non-commercial purposes in accordance with Wiley Terms and
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Midpalatal implants vs headgear for orthodontic anchorage - a randomized clinical trial: Cephalometric results
OBJECTIVE: To compare the clinical effectiveness of the mid-palatal implant as a method of reinforcing anchorage during orthodontic treatment with that of conventional extra-oral anchorage.
DESIGN: A prospective, randomized, clinical trial
Setting: Chesterfield and North Derbyshire Royal Hospital NHS Trust and the Charles Clifford Dental Hospital, Sheffield.
SUBJECTS AND METHODS: 51 orthodontic patients between the ages of 12 and 39, with a class II division 1 malocclusion and ‘absolute anchorage’ requirements were randomly allocated to either receive a mid-palatal implant or headgear to reinforce orthodontic anchorage. The main outcome of the trial was to compare the mesial movement of the molars and incisors of the two treatment groups between T1 (start) and T2 (end of anchorage reinforcement) as measured from cephalometric radiographs.
RESULTS: The reproducibility of the measuring technique was acceptable. There were significant differences between the T1 and T2 measurements within the implant group for the position of the maxillary central incisor (p<0.001), position of the maxillary molar (p=0.009) and position of the mandibular molar (p<0.001). There were significant differences within the headgear group for the position of the mandibular central incisor (p<0.045), position of the maxillary molar (p=<0.001) and position of the mandibular molar (p<0.001). All the skeletal and dental points moved mesially more in the headgear group during treatment than in the implant group. These ranged from an average of 0.5mm more mesial for the mandibular permanent molar to 1.5mm more mesial for the maxillary molar and mandibular base. None of the treatment changes between the implant and headgear groups were statistically significant.
CONCLUSIONS: Mid-palatal implants are an acceptable technique for reinforcing anchorage in the orthodontic patient
Midpalatal implants vs headgear for orthodontic anchorage - a randomized clinical trial: Cephalometric results
OBJECTIVE: To compare the clinical effectiveness of the mid-palatal implant as a method of reinforcing anchorage during orthodontic treatment with that of conventional extra-oral anchorage.
DESIGN: A prospective, randomized, clinical trial
Setting: Chesterfield and North Derbyshire Royal Hospital NHS Trust and the Charles Clifford Dental Hospital, Sheffield.
SUBJECTS AND METHODS: 51 orthodontic patients between the ages of 12 and 39, with a class II division 1 malocclusion and ‘absolute anchorage’ requirements were randomly allocated to either receive a mid-palatal implant or headgear to reinforce orthodontic anchorage. The main outcome of the trial was to compare the mesial movement of the molars and incisors of the two treatment groups between T1 (start) and T2 (end of anchorage reinforcement) as measured from cephalometric radiographs.
RESULTS: The reproducibility of the measuring technique was acceptable. There were significant differences between the T1 and T2 measurements within the implant group for the position of the maxillary central incisor (p<0.001), position of the maxillary molar (p=0.009) and position of the mandibular molar (p<0.001). There were significant differences within the headgear group for the position of the mandibular central incisor (p<0.045), position of the maxillary molar (p=<0.001) and position of the mandibular molar (p<0.001). All the skeletal and dental points moved mesially more in the headgear group during treatment than in the implant group. These ranged from an average of 0.5mm more mesial for the mandibular permanent molar to 1.5mm more mesial for the maxillary molar and mandibular base. None of the treatment changes between the implant and headgear groups were statistically significant.
CONCLUSIONS: Mid-palatal implants are an acceptable technique for reinforcing anchorage in the orthodontic patient
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