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Genetic variation refers to the differences in DNA among individuals within a species. This variation is a key factor in determining the heritability of traits. If a population exhibits high genetic diversity, it means there is a wide range of genetic material present, which can lead to different traits being expressed. Within the context of heritability, greater genetic variation allows researchers and breeders to identify how much of a trait’s diversity is due to genetics, as opposed to environmental influences.
In domesticated animals, like pigs, genetic variation is often controlled through selective breeding. Farmers and breeders choose animals with desirable traits to reproduce, which can both increase certain genetic variations and reduce others. This selective breeding process can amplify the influence of genetics on traits like weight, by ensuring that these traits are consistently passed down through generations.

Environmental variation encompasses all the non-genetic factors that can influence a trait. This includes factors such as diet, temperature, climate, and living conditions. For animals, particularly those in the wild like wild boars, such environmental factors lead to more variability in traits because the conditions they experience can change dramatically from one location or season to another.
Domesticated animals like pigs, however, experience less environmental variation. This is because their living conditions are typically more stable and controlled, including consistent feeding, temperature controls, and healthcare interventions. As a result, the weight of domesticated pigs is less affected by external environmental factors, allowing genetic differences to hold more sway in determining the weight of the pigs.

Domestication alters the genetic makeup of animals over many generations, leading to physical and behavioral changes. These changes are often seen in traits like size, appearance, and temperament. During domestication, animals are bred selectively to enhance traits that are beneficial or desirable for human purposes. This results in a reduced genetic variation among the domesticated group but often enhances certain traits, making them more prominent.
For example, domesticated pigs have been bred over time to meet specific dietary and growth needs, such as achieving a larger body mass quickly. This focus shifts the balance between genetic and environmental influences, often resulting in higher heritability for certain traits as the environmental effects diminish. Thus, domestication can lead to a higher genetic contribution to the variability seen in desirable traits.

Genetic contribution describes how much genetics can explain the differences observed in a particular trait within a population. In heritability studies, genetic contribution is assessed to determine what portion of the variation in a trait, like weight, is due to genetic factors rather than environmental ones.
With domesticated pigs, the structured and stable environments mean that less variation in traits is due to external conditions, highlighting the genetic contribution more significantly. Since many environmental variables are kept consistent, any remaining variation in weight or other traits is more likely due to underlying genetic differences. This leads to higher heritability scores, indicating that genetics play a more substantial role in domestic settings than in wild populations where environmental influences are much more unpredictable and varied.