are marked by grave goods and position, and in some areas, elite individuals are buried with complete wooden wagons. Grave goods are more common in eastern Yamnaya burials, which are also characterized by a higher proportion of male burials and more male-centred rituals than western areas. In the northern Pontic steppes were excavated the oldest wheels in the world, which may tentatively be associated with the Indo-Europeans. The Yamnaya culture had and used two-wheeled carts and four-wheeled wagons, which are thought to have been oxen-drawn at this time, and there is evidence that they rode horses. Metallurgists and other craftsmen are given a special status in Yamnaya society, and metal objects are sometimes found in large quantities in elite graves. New metalworking technologies and weapon designs are used. Diet stable isotope ratios of Yamna individuals from the Dnipro Valley suggest the Yamna diet was terrestrial protein based with insignificant contribution from freshwater or aquatic resources. Anthony speculates that the Yamnaya ate a diet consisting of meat, milk, yogurt, cheese, and soups made from seeds and wild vegetables, and probably consumed mead. Mallory and Adams suggest that Yamnaya society may have had a tripartite structure of three differentiated social classes, although the evidence available does not demonstrate the existence of specific classes such as priests, warriors, and farmers. Archaeogenetics According to Jones et al. (2015) and Haak et al. (2015), autosomal tests indicate that the Yamnaya people were the result of a genetic admixture between two different hunter-gatherer populations: distinctive "Eastern Hunter-Gatherers" (EHG), from Eastern Europe, with high affinity to the Mal'ta–Buret' culture or other, closely related people from Siberia and a population of "Caucasus hunter-gatherers" (CHG) who probably arrived from the Caucasus or Iran. Each of those two populations contributed about half the Yamnaya DNA. This admixture is referred to in archaeogenetics as Western Steppe Herder (WSH) ancestry. Admixture between EHGs and CHGs is believed to have occurred on the eastern Pontic-Caspian steppe starting around 5,000 BC, while admixture with Early European Farmers (EEF) happened in the southern parts of the Pontic-Caspian steppe sometime later. More recent genetic studies have found that the Yamnaya were a mixture of EHGs, CHGs, and to a lesser degree Anatolian farmers and Levantine farmers, but not EEFs from Europe due to lack of WHG DNA in the Yamnaya. This occurred in two distinct admixture events from West Asia into the Pontic-Caspian steppe. Haplogroup R1b,