Answers below, one by one
Explanation:
1. Homo erectus hunters killed the animals whose bones have been found together with Acheulean tools
<em>Acheulean</em> tools are 'hand axes', a tool made of stone which main feature is an oval or a 'peared 'shape. These have been associated to <em>Homo erectus </em>and derived species, such as <em>Homo heidelbergensis. </em>
Such technology was created and used during the Lower Palaeolithic era, geographically found in Africa, a wide parte of West Asia, South Asia, East Asia and Europe, and come typically together with <em>Homo erectus</em> remains. It is thought that <em>Acheulean</em> technologies derived from a previous kind of technology called <em>Oldowan</em>, which has been associated to <em>Homo habilis. </em>
Let's keep in mind that usually the technology that characterized a period would be the kind of tool that might have been used mostly by that group. Therefore, if we put all the information together, it would be easy to deduct that animal bones found together with <em>Homo erectus</em> remains and tools could come from a hunted one. However, we should also keep in mind that there exists a possibility on this, but not necessarily all the remains found together mean the animals were killed by that subject, since there is a chance that animals and humans with their tools were buried together as a part of a death ritual.
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2. Homo erectus used fire to cook the meat of the animals whose bones have been found in association with Homo erectus remains
Hearths are campfires that have been found as evidence, and the earliest ones belong to <em>Homo erectus</em> period. In the hearths, evidence shows that these were used for cooking and maybe sharing food. It would be pretty logical to think that bones found in association with <em>Homo erectus </em>remains could have been from the animals they might have cooked and consumed. If this was correct, also hearths or campfires could have been places where social interaction, warmth and large predators defence may have happenned.
3. Homo erectus practiced cannibalism
The first reason that comes to mind to explain prehistoric cannibalism is dietary motivations - since probably these species were opportunists to eat, as a part of daily survival.
Despite this could be the most popular idea, we still should consider that social motivations (meaning social interaction and complexity in them) could have played an important role in why acts of cannibalism took place. This means there cannot have been a single reason; it is believed that human flesh provides a poor calorific return.