Evolution
 1998
DOI: 10.1111/j.1558-5646.1998.tb01823.x
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The Population Genetics of Adaptation: The Distribution of Factors Fixed During Adaptive Evolution

H. Allen Orr
1

Abstract: We know very little about the genetic basis of adaptation. Indeed, we can make no theoretical predictions, however heuristic, about the distribution of phenotypic effects among factors fixed during adaptation nor about the expected "size" of the largest factor fixed. Study of this problem requires taking into account that populations gradually approach a phenotypic optimum during adaptation via the stepwise substitution of favorable mutations. Using Fisher's geometric model of adaptation, I analyze this approa… Show more

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Cited by 875 publications

(906 citation statements)
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“…Furthermore, the underlying distribution of parameter effect sizes for the sampled mutations is constant across all steps of the trajectories and the form of this distribution does not qualitatively affect the results. Our finding that the largest steps are not fixed first runs counter to some well‐established theoretical results for adaptive walks, which predict an exponential distribution of mutation sizes over trajectory steps (Orr 1998; Rokyta et al. 2005; Joyce et al.…”
Section: Discussioncontrasting
confidence: 95%
Exaggerated anticipatory anxiety is common in social anxiety disorder (SAD). Neuroimaging studies have revealed altered neural activity in response to social stimuli in SAD, but fewer studies have examined neural activity during anticipation of feared social stimuli in SAD. The current study examined the time course and magnitude of activity in threat processing brain regions during speech anticipation in socially anxious individuals and healthy controls (HC). Method Participants (SAD n = 58; HC n = 16) underwent functional magnetic resonance imaging (fMRI) during which they completed a 90s control anticipation task and 90s speech anticipation task.
show abstract
“…Furthermore, the underlying distribution of parameter effect sizes for the sampled mutations is constant across all steps of the trajectories and the form of this distribution does not qualitatively affect the results. Our finding that the largest steps are not fixed first runs counter to some well‐established theoretical results for adaptive walks, which predict an exponential distribution of mutation sizes over trajectory steps (Orr 1998; Rokyta et al. 2005; Joyce et al.…”
Section: Discussioncontrasting
confidence: 95%
Exaggerated anticipatory anxiety is common in social anxiety disorder (SAD). Neuroimaging studies have revealed altered neural activity in response to social stimuli in SAD, but fewer studies have examined neural activity during anticipation of feared social stimuli in SAD. The current study examined the time course and magnitude of activity in threat processing brain regions during speech anticipation in socially anxious individuals and healthy controls (HC). Method Participants (SAD n = 58; HC n = 16) underwent functional magnetic resonance imaging (fMRI) during which they completed a 90s control anticipation task and 90s speech anticipation task.
show abstract
“…Figure shows this distribution in adaptive‐walk simulations with n=2 traits. The marginal distribution in the direction of the optimum has an intermediate mode and resembles a gamma distribution, in accordance with previous results for the one‐dimensional moving‐optimum model (Kopp and Hermisson ), and in contrast to the exponential pattern predicted for the classical Fisher model with constant selection (Orr ). Although the population always follows the optimum, pleiotropic side effects of fixed mutations frequently lead to maladaptation of the traits under pure stabilizing selection.…”
Section: Resultssupporting
confidence: 90%
Exaggerated anticipatory anxiety is common in social anxiety disorder (SAD). Neuroimaging studies have revealed altered neural activity in response to social stimuli in SAD, but fewer studies have examined neural activity during anticipation of feared social stimuli in SAD. The current study examined the time course and magnitude of activity in threat processing brain regions during speech anticipation in socially anxious individuals and healthy controls (HC). Method Participants (SAD n = 58; HC n = 16) underwent functional magnetic resonance imaging (fMRI) during which they completed a 90s control anticipation task and 90s speech anticipation task.
show abstract
“…Our findings are consistent with previous experimental and theoretical issues on adaptation (Orr 1998; Hurme et al . 2000).…”
Section: Discussionsupporting
confidence: 93%
Exaggerated anticipatory anxiety is common in social anxiety disorder (SAD). Neuroimaging studies have revealed altered neural activity in response to social stimuli in SAD, but fewer studies have examined neural activity during anticipation of feared social stimuli in SAD. The current study examined the time course and magnitude of activity in threat processing brain regions during speech anticipation in socially anxious individuals and healthy controls (HC). Method Participants (SAD n = 58; HC n = 16) underwent functional magnetic resonance imaging (fMRI) during which they completed a 90s control anticipation task and 90s speech anticipation task.
show abstract
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