The animals were a big part in why Eurasia was the champion of history. The livestock not only provide a way of transportation but also food and some even milk. Once the people had domesticated the animal they could use it to help the grow crops an with the help the could produce more food to feed more of the community. They even had food to feed all the animal that they domesticated.
Livestock are important because if they ate the animal that itself produced a lot of nutrition. If the people only ate fruits and vegetables then they wouldn't have been as strong as they were. Also they could use the skin of the animal as clothing or even to build a tent. It was important that they stay warm during cold temperatures in order to live.
The livestock were the muscles! Yes, before the animal they had to use the human but if you think about it, how much could a person really do? Of course the animal was stronger and could handle more labor than a person can. That is why with animals they were able to produce more and more crops to feed more and more of their community.
The written language was important for the people but it didn't get them more food and muscle power it just allowed them to communicate. Although communication was important, at the time, the livestock was far more useful and necessary for life.