The article by Loeske E. B. Kruuk reviews the application of restricted maximum-likelihood 'animal models' to multigenerational data from natural populations, highlighting their utility in estimating variance components and predicting breeding values. These models are particularly valuable for addressing the confounding effects of environmental variation and generating new areas of investigation in evolutionary biology. The author discusses the paradox of continued genetic variation under selection and the mismatch between theoretical quantitative genetics and empirical observations from natural populations. The introduction of mixed models, specifically the animal model, has facilitated more accurate analysis of evolutionary dynamics. The article outlines the key components of the animal model, including fixed and random effects, and explains how these models can estimate variance components and predict breeding values. It also reviews studies using animal models in wild populations, such as red deer and collared flycatcher populations, and discusses the importance of establishing pedigrees and accounting for common environment effects, maternal effects, and repeated measures. The review emphasizes the potential of animal models to provide critical insights into the evolutionary ecology of natural populations.The article by Loeske E. B. Kruuk reviews the application of restricted maximum-likelihood 'animal models' to multigenerational data from natural populations, highlighting their utility in estimating variance components and predicting breeding values. These models are particularly valuable for addressing the confounding effects of environmental variation and generating new areas of investigation in evolutionary biology. The author discusses the paradox of continued genetic variation under selection and the mismatch between theoretical quantitative genetics and empirical observations from natural populations. The introduction of mixed models, specifically the animal model, has facilitated more accurate analysis of evolutionary dynamics. The article outlines the key components of the animal model, including fixed and random effects, and explains how these models can estimate variance components and predict breeding values. It also reviews studies using animal models in wild populations, such as red deer and collared flycatcher populations, and discusses the importance of establishing pedigrees and accounting for common environment effects, maternal effects, and repeated measures. The review emphasizes the potential of animal models to provide critical insights into the evolutionary ecology of natural populations.