4. Discussion
So far, based on the faunal records of Late Neolithic-Copper Age settlements in southern Iberia, it is clear that sheep and goat husbandry held a prominent position alongside pig farming. Pig remains are often found in large quantities, which can be interpreted as evidence of collective consumption events [
37]. Domestic caprines were the best-adapted animals to the environment and held a predominant economic role in the region from the Neolithic to the Roman periods. On the other hand, pig remains are usually easier to identify due to their distinct anatomical features, whereas many domestic caprine remains are classified as indeterminate mesomammals, leading to their underrepresentation [
3].
In general terms, without delving into the environmental and geographical characteristics of each habitat, it seems that the primary meat source for these human communities was provided by pigs, supplemented by ovicaprid and bovine sacrifices.
Regarding ovicaprids, during this period, there is no evidence to refute the hypothesis that goats and sheep were managed in separate flocks. However, recent studies have shown that mixed herds enhance efficient resource utilization in pasture systems. This synergy arises from the complementary feeding habits of the two species: sheep primarily graze on low-lying grasses, while goats exhibit a preference for browsing on shrubs and higher vegetation. This grazing behavior not only reduces competition for food but also promotes a more extensive growth of ground-level grasses, as goats consume shrubs and reduce vegetative overgrowth, which frees space for grass growth [
60]. Goats exhibit more exploratory and aggressive behavior then sheep, and due to their vocalizations and high state of alertness, can serve as effective sentinels, potentially warning the herd of the presence of a predator. Additionally, in extensive grazing systems, the role of an experienced, older goat often proves valuable in guiding movements of the herd, thus facilitating group cohesion [
61]. All these reasons suggest that sheep and goats could have been managed together in single, mixed herds during the late fourth and third millennia BC. Recent advances in geoarchaeological studies of stabling floors could shed light on this issue; however, for now, the ethnoarchaeological results are promising [
62].
Regarding the different sites, based on the number of identified bones remains and the minimum number of individuals, in most cases, sheep had higher prevalence than goats. A study on aDNA and the application of ZooMS analysis suggest a possible overrepresentation of goats when using the osteomorphological criteria of Zeder and Pilaar (2010), which are based on mandibular teeth to distinguish between sheep and goats [
63]. In any case, even when accounting for a possible overestimation of goat remains compared with sheep, herds contained a majority of sheep over goats during the late fourth and third millennia BC. This preference may be attributed to the generally docile nature of sheep, which likely facilitated their management and grazing especially in the Guadalquivir Basin, which is rich in pastures and gentle orography (
Figure 2).
In other regions of Europe, in Neolithic and Copper Age contexts, sheep farming seems to have focused on meat production [
64]. The same occurred at different sites of the Iberian Peninsula such as Mercador (Mouräo, Portugal), Penedo do Lexim (Mafra, Portugal) and La Minilla (La Rambla, Córdoba), where the mortality rate of individuals younger than 24 months might indicate a meat-based use [
5,
20].
However, in the cases of Cabezo Jure (Alosno, Huelva), Ciudad de la Justicia (Jaén), IA Corte Inglés (Jaén), Les Moreres (Crevillent, Alicante), Monte da Tumba (Torräo, Portugal), and Perdigões (Reguengos de Monsaraz, Portugal), the slaughter or death of the sheep predominantly occurs during juvenile or adult stages [
16,
22,
32,
34], which suggests a comprehensive exploitation of the livestock, not only for meat, but also for secondary resources such as wool, milk, hides, manure, etc. Lastly, data from the mid-3rd millennium BC at Los Castillejos de Montefrío (Montefrío, Granada), Marinaleda (Sevilla), and Ota (Alenquer, Portugal) reveal a high number of adult individuals, which could indicate a trend towards the exploitation of these secondary products. Faunal studies of Late Neolithic-Copper Age settlements with the most identified and individualized sheep remains show the difficulty in differentiating between Ovis/Capra in infant and juvenile specimens. At Valencina de la Concepción (Sevilla), the age of death or sacrifice is assessed based on the ovicaprid group, with one-fifth of the animals being slaughtered before the age of nine months, and slightly less than half being older than two years [
9]. The same was found at Zambujal, where a joint assessment of the age of ovicaprids estimated 180 individuals under two years of age and 194 individuals older than two years [
7].
The presence of loom weights, crescent-shaped objects, and 'cheese strainers' in archaeological contexts could also be associated with the exploitation of secondary products (wool and milk), whereas their absence might indicate otherwise. One clear example of this is the settlement of Les Moreres (Crevillent, Alicante), where a large number of crescents and loom weights were recovered from two huts dating to the final centuries of the Copper Age [
65], which are related to textile and weaving production. The presence of
Ovis aries has been confirmed in this context [
23]. Conversely, at Mercador, the absence of these artifacts suggests a meat-based exploitation of sheep [
20].
However, it is essential to approach these findings with caution, as the earliest known textile discoveries in the Iberian Peninsula were of plant-based fibers. [
66]. In some cases, the bias in faunal information that reaches us through the archaeological record should be supplemented with other analytical methods to clarify whether sheep and goat husbandry were being used. A recent study on lipids found inside Neolithic ceramics demonstrates that in the northern and Atlantic regions of the Iberian Peninsula, ovicaprine livestock was already being exploited for both meat and dairy production [
67].
The isolated discovery of the “flint dagger” from Wiepenkathen (Germany), found in a peat bog by farmers in 1935 and typologically dated to the Late Neolithic, was encased in a sheath made of sheep leather, decorated with a vegetal pattern. The straps wrapping the artifact were made of cattle hide, the wooden handle was covered with textile fibers from sheep, horse, cow, and goat, and the warp threads were made of plant fibers. This represents the oldest evidence of the use of wool in Europe [
68]. However, there has always been an ongoing debate among scholars about the role of sheep as wool producers [
69,
70], with a more conservative view suggesting the probable absence of woolly sheep breeds in Western Europe before the 3rd millennium BCE [71-73]. The earliest evidence of woolen textiles in southern Iberia is associated with an early Bronze Age burial [
74].
The secondary resources of ovicaprids are principally milk and wool. In ovicaprid husbandry, it has historically been shown that goats are more productive in terms of milk yield [
75]. Non-improved sheep breeds provide milk to their offspring for approximately 135 days, with a daily milk yield ranging between 0.21 and 0.33 liters per animal [
75]. In this context, goats produce more milk than sheep, in some cases doubling the annual milk production in kilograms [
76]. Ewes start producing milk between 12 and 18 months after their first lambing, with the age of highest production being between 3 and 5 years [
77]. On the other hand, sheep start to produce wool from 12 months, but it is between 2 and 4 years of age that they are most productive. Normally it is from the age of 6 years that ewes start to produce less, and poorer quality, wool [
78]. Therefore, the prevalence of sheep in these herds could be due, in addition to their greater docility, to the exploitation of wool, rather than for dairy production, which is higher in goats.
Several studies have attempted to describe the domestication processes of sheep and the origins of current breeds through genomic analyses [79-81]. However, only few works analyze ancient DNA (aDNA) from bone remains, and all of them employed only mitochondrial approaches [
63,
82,
83]. However, recently, paleogenomic techniques have been used to infer domestication process on
Caprinae subfamily from Neolithic [
84]. In fact, to our knowledge, this is the first study to employ genomic approaches in ancient DNA focused on production uses during the late fourth and third millennia BC.
Currently, the Spanish Merino breed is considered the origin of all contemporary Merino breeds and their derivatives [
85]. The oldest written reference to sheep from southern Iberia comes from Columella (42 A.D.), in his work Res Rustica. Here, he describes the crossbreeding practices utilized by his uncle Marcus used to obtain higher-quality wool, noting that white wool is preferable for its ease of dyeing. Additionally, he highlights the value of the dark and blackish fleece of sheep in Italy (Polentia) and in Baetica (Córdoba). In this study, we go back to the late fourth and third millennia BC to investigate the native sheep of the Iberian Peninsula, which later would serve as the basis used by the Romans to establish the genetic stock that would later give rise to the Spanish Merino sheep [
85]. Genomic assays showed how individuals from the Marinaleda breed were highly heterogeneous both in terms of multilocus heterozigosity and inbreeding coefficiency, reflecting individuals with different genetic variants (
Figure 3a,b). In fact, three of the samples had similar values, which could indicate that they may belong to the same herd. Individuals from La Minilla reflected this trend more clearly and explicitly in its two individuals, which, according to the inbreeding coefficient, could be related in some degree.
The young males kill-off model is one of the strongest arguments used to support domestication events, and has been observed in several Neolithic sites in south-western Asia [
86]. The Chalcolithic context of the present study situates it in a time of management events of already domesticated livestock. Thus, one key element that supports the concept of a managed herd structure is the finding that 100% of the samples analyzed were female. This observation aligns with the management practices that have been in place from historical periods to the present, which typically maintain a high female-to-male ratio, estimated at approximately 1 male for every 30 to 50 females [
87].
Moreover, it is important to note that the samples used in the genomic analysis comprised adult animals rather than juveniles, where one might expect to observe a female-to-male ratio closer to 1. This discrepancy further emphasizes the implications of management strategies on population dynamics and genetic diversity. However, in the prehistoric communities we have studied, males held a prominently symbolic role, as evidenced by the deposits of butchered crania found at some sites in southern Iberia [
3,
30].
The aDNA samples from the studied sheep are grouped by their genomic homology based on the site of origin (
Figure 4 and
Figure 5a). The differences observed may be attributed to a temporal separation of as much as 941 years between the earliest and latest dates at the various sites, according to the radiocarbon dating (
Table 2), which may have led to a substantial accumulation of genomic variants. This could have resulted in sheep we assume proceed from a common genetic base becoming highly differentiated due to breeding processes related to the management practices of each time period and geographic locations. However, the archaeological records suggest that, during this period, management practices were conducted in a highly similar way, and that these populations did not accumulate as much genetic change as is seen in modern breeds. Thus, we can assume that the differences found are due to the redistribution of allele frequencies that occurred due to the particularities of management and the specific environmental conditions of each geographical location, as observed in modern herds of the same breed [
88].
Although the genetic distances between sites are not very large (approximately between 0.08 and 0.12), it is evident that the most genetically similar animals are those from La Minilla and Marinaleda, while the most genetically distant are those from Grañena Baja and La Minilla (
Figure 6). Nevertheless, we have detected a significant level of genetic homology between samples from two different sites. Specifically, an individual from Marinaleda (FOS82) shows genetic similarity with an individual from Grañena Baja (FOS113), as illustrated in the dendrogram of genetic distances (
Figure 5a,b).
The fact that all the Copper Age samples have more genetic similarities between them than with some of the modern breeds can be explained by the extensive process of selection that has taken place over the last few centuries in these breeds (
Figure 7). In fact, in the last decades, increased professionalization and new diagnostic techniques have meant that selection has developed into genetic improvement. Proof of this is the large number of livestock breeds which have their own breeding program. However, when we analyze the samples individually, we can determine, based on genetic distances, the level of homology they may have with samples of current breeds (
Figure 8).
At the Marinaleda site, most of the samples analyzed are equidistant from the current breeds, but with greater similarity to the Black Merino, a trend that is also observed in the Grañena Baja site (
Figure 8a,c). However, one of the samples (FOS059) showed similar genetic distances to ME and MN. This could indicate that this individual resembles the endemic animals, but with some features of breeds with greater wool aptitude.
At the La Minilla site, however, the remains are genetically closer to one of the white Merino samples, and very close to the two samples of the Segureña breed (
Figure 8b). In other words, these sheep are genetically close to modern breeds with a marked aptitude for meat use. In the case of the Minilla, the animals slaughtered in general were young (males and females), which could indicate a management more focused on meat production where secondary products such as milk and wool would not have such importance for obtaining local resources [
5].
This is the first work to analyze the aDNA of sheep from the late fourth and third millennia BC in the Iberian Peninsula, in which we suggest the presence of different types of management, both of primary and secondary products. This may provide an important knowledge base for further research on the sheep that are believed to have derived from the first Merinos.