RESUMEN
Cumulative cultural evolution, the accumulation of sequential changes within a single socially learned behaviour that results in improved function, is prominent in humans and has been documented in experimental studies of captive animals and managed wild populations. Here, we provide evidence that cumulative cultural evolution has occurred in the learned songs of Savannah sparrows. In a first step, "click trains" replaced "high note clusters" over a period of three decades. We use mathematical modelling to show that this replacement is consistent with the action of selection, rather than drift or frequency-dependent bias. Generations later, young birds elaborated the "click train" song form by adding more clicks. We show that the new songs with more clicks elicit stronger behavioural responses from both males and females. Therefore, we suggest that a combination of social learning, innovation, and sexual selection favoring a specific discrete trait was followed by directional sexual selection that resulted in naturally occurring cumulative cultural evolution in the songs of this wild animal population.
Asunto(s)
Evolución Cultural , Passeriformes , Animales , Animales Salvajes , Femenino , Humanos , Aprendizaje/fisiología , Masculino , Vocalización Animal/fisiologíaRESUMEN
BACKGROUND: Lymph node involvement is a highly important prognostic factor in colorectal cancer staging. Examination of a minimum of 12 nodes is recommended for accurate staging. The purpose of this study was to identify factors affecting the number of lymph nodes harvested in colorectal cancer specimens. MATERIALS AND METHODS: Retrospective review of all patients undergoing colectomy for colorectal cancer at our VA hospital from 2002 to 2007 was done. Statistical analysis was done using univariate as well as multivariate analysis. One hundred eighty-three patients were analyzed. RESULTS: Average number of nodes retrieved was 14.9 with 92 (51%) containing fewer than 12 lymph nodes. Median number of nodes was 11. The only two factors found to have an effect on nodes harvested were pathologist P<0.05 and surgeon experience P=0.01. Factors not found to have an impact on number of nodes harvested were age of patient, previous operation, T stage of tumor, type of colectomy, bowel prep, laparoscopic versus open technique, or BMI. Multivariate analysis confirmed pathologist and surgeon experience as independent factors associated with number of nodes retrieved P<0.05. CONCLUSIONS: Operating surgeon and examining pathologist were the only factors found to have a significant impact on number of nodes harvested. Meticulous dissection both in and outside of the operating room are indicated.