Live Chat
Evolution of Pigs

Evolution of Pigs

In different countries of the world, a great variety of pigs is diversified in both color and size. Many of them were bred on the basis of crossing various types of pigs, sound selection of the best animals, selection by the desired type, and directional rearing of new generations. By isolating pigs from the natural environment, people created completely different living conditions for them, changed their feeding and housing patterns, and decisively interfered with the breeding processes. As a result, domestic pigs became significantly different from their wild ancestors. However, their evolution was not only through artificial selection. An essential role in the modification of animals played natural selection. Thus, the purpose of this work is to analyze the factors of the natural and artificial evolution of pigs. Methods of analysis and synthesis of scientific information on individual aspects of the evolution of pigs made it possible to draw a number of conclusions. Firstly, there is no single theory regarding the origin of pigs. Secondly, the modern appearance of the pig and wild boar differs significantly from the physical characteristics of their ancestors. Finally, at the present stage, the natural and artificial selection of pigs are imbalanced, and this requires the modernization of the rearing of these animals.

Pig breeding is one of the most effective and early maturing branches of animal husbandry. The main products of the pig industry are meat and lard, but people have also learned to use leather in the leather industry, bristles in the light industry, and blood in preparing medicines and feed products. A high proportion of pork in comparison with other types of meat consumed by people is associated with the biological characteristics of animals of this species. Among the main features of rearing pigs are singularity, multiplicity, precocity, and the efficiency of feed, as well as the excellent taste and dietary quality of pork. However, people were not able to use the full potential of this animal immediately. The modern pig has appeared after centuries of evolution. The species developed as a result of natural selection and human activity and has undergone significant changes in its form, muscle structure, fertility, and speed of gaining weight.

Origin of Pigs

The modern domestic pig (Sus domestica) is a product of centuries-old evolution, during which the species developed under the influence of natural selection and human activity. According to the classification of animals, a domestic pig belongs to the type of vertebrates, the class of mammals, the order of the artiodactyls, the family of pigs, and the genus of the pig (Evin et al., 2017). The genus includes the preserved wild ancestral forms (wild boar) and the domestic pig. There are two points of view on the wild ancestors of the pig. The first is that all modern breeds of pigs come from three forms: Sus scrofa vittatus (wild boar of Southeast Asia), S.s. Mediterranean (Mediterranean wild boar), and S.s. scrofa (wild cab of Central Europe and North Asia) (Ni et al., 2018). The second theory recognizes only two initial forms: the European and Far Eastern wild boars (Ni et al., 2018). It is believed that the domestication of the pig occurred about 6-7 thousand years ago in China (Evin et al., 2017). However, it is difficult to establish the true origin of the modern domestic pig with certain accuracy.

The domestication of the pig, as well as of other animal species, occurred in connection with the transition from a nomadic hunting lifestyle of a human to sedentary agriculture. When people began to unite into tribal communities and hunting tools improved more slowly than social relations, the need for the domestication of animals arose. The process of keeping animals in pens led to the use of selection: first of all, those animals who tried to escape were killed and used for different needs of people, while calmer animals were kept (Evin, Dobney, & Cucchi, 2017). The opportunity to get pigs’ offspring in captivity forced people to engage in fodder production. The development of agriculture and animal husbandry greatly promoted the breeding of these animals. The nomads used them mainly for movement, while the sedentary communities associated their existence with the breeding of such species that would provide them with different products. Pig as a source of meat has become one of the main objects of human labor. The very fact of domestication was the starting point for huge transformations, the depth and forms of which began to accelerate, becoming an integral part of the civilization process of humanity.

Features of a Wild Boar and a Pig

The modern wild boar is not an exact copy of the ancestor of the domestic pig, as evidenced by the different karyotypes. The domestic pig has 38 somatic chromosomes (19 pairs), while the wild boar has 36 (Frantz et al., 2015). However, the differences do not prevent these forms from easily crossing, giving an interspecific hybrid with an intermediate number of chromosomes of 37 (Frantz et al., 2015). Consequently, only animals of a certain species were domesticated, although wild boars influenced their evolutionary changes through the crossing.

The characteristics of the wild boar are radically different from those of the modern domestic pig. To determine what changes have occurred in the biology of pigs during evolution, it is necessary to compare the main features of the wild boar and animals of primitive breeds (Frantz et al., 2015).

Features of domestic pigs (primitive breeds)

Features of Wild boar

The dental system finishes its development until the pig’s 17-18th month of life.

The dental system is developed by the end of the 36-40th month of life.

The skull is short and wide; in 4-year-old sows, the zygomatic width is 53.6% of the main length.

In three-month-old piglets, the zygomatic width of the skull is 54.8% of the main length, and in 4-year-old boars, it is only 44.6%.

The main ratio of the parts of the skull is set at the age of 11-12 months.

The ratio of parts of the skull is set by 3-3.5 years.

The tubular bones of the limbs are relatively short, with mild tubercles, ridges, and roughness.

The tubular bones of the extremities with underdeveloped mounds, ridges, and roughness are observed only in piglets up to 7-8 months old.

Ossification of the skeleton ends at the age of 20 – 24 months.

Metaepiphyseal cartilages in tubular bones disappear only by 3-3.5 years.

Thorax is round (relatively wide and shallow).

In piglets the ribcage is round; in adults, it is flat and deep.

The height at Withers is relatively small.

The height at withers is small only for young wild boars. Withers of adult females and especially males are relatively high.

Undercoat is underdeveloped or missing.

The undercoat is absent only in newborn piglets.

The ability to reproduce mainly coincides with puberty (6-9 months).

Boars reach sexual maturity at the age of 7–8 months, but in fact, females begin to participate in reproduction at the age of 19–20 months, and males – at the age of 42–44 months.

High fecundity: give two litters per year, which amount to 6-10 piglets per year.

Low fecundity: give one litter per year on average 4-6 piglets.

Piglet’s weight at birth is 0.62-1.2 kg.

Pigs are born weighing 0.9-1.05 kg.

Weight in one-year-old age is 82 kg, in three years it is 108 kg.

At the end of the third year of life (spring), they weigh 76–79 kg; the boar weighs over 100 kg in the autumn season, starting from the third year of life.

Able to accumulate fat in the subcutaneous tissue at any time of the year.

Fat accumulates only in late summer and autumn.

Are active in the daytime.

Are active at twilight and at night.

If to assume that the wild ancestors of the pig possessed approximately the same properties as the modern wild boar, then significant morphophysiological differences between them and primitive breeds are seen solely due to the factor of domestication. At the same time, primitive and factory breeds differ mainly in productive traits caused by the intensive selection of animals of the desired type and the creation of appropriate housing and feeding conditions. The biological basis of such changes is a significant transformation of the level and type of metabolism and energy in the cells and tissues of animals (Frantz et al., 2015). These qualities, fixed and developed by artificial selection, led to changes in the relative performance of organs and tissues. From the above comparative characteristics, it follows that in the course of evolution, the pig has more young stages of development, is more plastic, and is susceptible to changes in conditions of unstable environment and artificial selection.

Morphogenetic Changes in Pigs

The morphogenetic changes of the pigs took place under the complex influence of the factors of domestication and selection. At the first stage of domestication, people selected pigs depending on their behavior, choosing calm and less mobile ones, which led to the simplification of the brain morphology and the weakening of vision, while the ability to distinguish colors (day vision) appeared (Evin et al., 2017). Not only the mass of pigs changed but also the muscle structure, which improved pigs’ ability to gain fat. The efforts of people to develop pigs’ ability to consume a large amount of different feed contributed to the formation of the habit of overeating, and this happened against the background of omnivorous preservation, which was the reason for the creation of breeds with high feed increment.

Recent studies show that domestication changes in animal genetic programs primarily concern not structural genes that encode proteins, but regulatory ones, which determine the phenotype of traits that existed in distant ancestors in a recessive state (Frantz et al., 2015). The evolutionary changes noted above indicate that the forms of the skull of the modern pig at the early stages of ontogenesis are characteristic of the most ancient subspecies of the wild pig of Southeast Asia (Evin, Dobney, & Cucchi, 2017). The development proceeds according to the principle of the fallout of the final stages and the preservation of more plastic stages, which took place phylogenetically earlier; this introduced new ways of the development of pig breeding in modern conditions. The most significant evolutionary acquisition was the ability of domestic pigs to be year-round sexually active and have high fertility (Ni et al., 2018). This property can be considered a synthesis of the influence of natural and artificial selection. The result of this process was a reduction in the viability of the individual animal, a relatively high viability of the species as a whole, and compensation for reducing the duration of breeding.

Domestication of Pigs

In the first period of domestication, pigs differed little from wild boars in body shape. They had a flat deep body, long legs, a large head with a long straight snout, erect ears, and a high bristle comb along the entire back. By 500-400 BC, the appearance of European pigs has already changed (Evin, Dobney, & Cucchi, 2017). In the Mediterranean region, a new type appeared with a concave back, drooping ears, a deep body, a short and broad head, and clearly expressed tenderness of physique. However, in all other parts of Europe, more primitive, although quite diverse types, prevailed. They differed in size; they were larger, long-legged and had the ability to gain fat (Ni et al., 2018). Still, for all primitive aboriginal breeds, a heavy head with a straight snout, low growth rate, feed allowance, and fecundity were typical (on average, 4–6 pigs per forage) (Ni et al., 2018). Their color was the most diverse, and the hair was of a complex structure.

The most characteristic feature of breed formation is the spontaneous selection and unsystematic crossing based on the principle of geographic proximity. This process was slow. The decisive factor in the evolution of the pig until the middle of the eighteenth century was that there was an even greater separation of animals from the natural environment and the creation of artificial conditions in their lives (Evin, Dobney, & Cucchi, 2017). Low productivity, poorness and unsatisfactory, rather primitive methods of production were the conditions for the predominant influence of natural selection on evolution. The peculiarity of such selection in the conditions of domestication was a higher intensity, as a result of which the modification and phenotypic variability of separate pigs became more pronounced compared to wild animals. Minor positive deviations were supported by natural selection, the main task of which was to stabilize the signs and properties, to ensure that each pig complied with the usual rate, and the most appropriate permanent habitat conditions. When being bred, the new qualities and properties of the pigs in the overwhelming majority are non-adaptive; therefore, they are most subject to the pressure of natural selection.

Artificial Selection of Pigs

From the moment when people consciously began to apply the selection of pigs of the desired type and special breeding methods, selection became the most effective factor of evolution. The best results are obtained only when the goals of artificial selection coincide with those of the natural one. For example, the latter occurs by reproductive ability and increased viability of the offspring. However, artificial selection has always been aimed at increasing meat and fattening ability, i.e. development of such properties that are opposite to the natural evolution of the species. This contradiction is the essence of the biology of the pig (Frantz et al., 2015). In other words, at the present stage of development of pig breeding, just as in other branches of animal husbandry, the questions of the relationship between natural and artificial selection and the skillful use of various forms of selection to achieve breeding goals arise. The main way to solve these contradictions is to improve the technology of feeding and housing and create such genotypes that are more adapted to breeding in specific conditions.

One of the factors in the intensification of artificial selection was the process of crossing different breeds and types of pigs. This process began in England in the eighteenth century (Evin, Dobney, & Cucchi, 2017). The resulting mixtures were distinguished by increased precocity, i.e. accelerated developmental stages. New types of pigs were selected for breeding, which, by many indications, repeated the ontogeny of ancestors at earlier stages of development. New acquisitions enjoy the highest development with a successful selection of parental forms, but they are very unstable and require stricter selection and maintenance of living conditions to preserve their offspring. Deterioration of these conditions leads to the loss of weight in the next generations and a partial return to the previous forms, which means a decrease in productivity.

Changes in the Structure of Pigs

Particularly significant changes in size and the speed of growth of pigs began to appear when the selection started to apply the achievements of genetics. The most important factor was the transition from the assessment of the phenotype to the assessment of the producers’ genotype, which has greatly accelerated the process of transforming pig breeds in the desired direction (Evin et al., 2017). Both the improvement of existing breeds and the creation of new ones aimed at increasing various factors of productivity of pigs – meat, feeding, and gaining fat (Evin et al., 2017). Modern pigs have undergone significant changes in body weight. The live mass of modern breeds is given in the table below (Frantz et al., 2015).



Weight, kg













Large white



North Caucasus



Large Black



White short-eared



Early meat




Data on three American and six European breeds shows that European pigs are much larger, which is the result of the direction and intensity of the use of breeding stock. In the United States and a number of Western European countries, an early meat type was formed with a very low duration of the use of sows and boars (Frantz et al., 2015). Despite the somewhat worse fertility, breeding small pigs in conditions of intensive production is more profitable than large ones (in terms of the use of premises, feed, and the complexity of care).

Modern Pig Breeding

Currently, the economic factor has become the dominant condition for breeding since producers aim to get more high-quality products at the lowest production cost. Evolution ranged from primitive forms to modern highly productive breeds and types, while natural selection was increasingly replaced by artificial. However, under the conditions of advancement of intensive industrial technologies, the effectiveness of the use of pigs with high productive potential, even with the creation of optimal feeding and housing conditions, remains very low on the scale of herds and breeds. The reason for this is the sharply increased susceptibility of pigs to diseases, and the reduction in the duration of breeding (Samore & Fontanesi, 2016). The difficulties that arose were due to the imbalance of natural selection, which is responsible for preserving the vitality of animals, and artificial one, which is aimed primarily at creating highly productive forms and types. Therefore, a further increase in productivity should be limited so that excessive specialization of the type does not entail a sharp increase in the cost of production of pigs.


The wide variety of existing species of pigs indicates the diversity of the original forms of ancestors, as well as the intensity of changes in the species due to domestication and artificial selection. There are two main approaches to the origins of the modern pigs. It was established that for the first time, a pig was domesticated in China; however, it is not possible to establish a clear origin of this animal. The modern class of pigs is represented by a wild boar and domestic pig, which retained some of the characteristics of their primitive ancestors. The morphological changes of the pig acquired in the process of evolution and artificial selection are connected with an increase in fertility, body weight, and muscle structure in the form of fat. Natural evolution and artificial selection are in imbalance at the present stage, therefore the subsequent rearing of pigs requires modernization.