Final answer:
Homo erectus is most significantly known for being the first human species to use fire, evidenced by archaeological finds such as ancient hearths and charred bones dating back around 1.7-2.0 million years ago.
Step-by-step explanation:
The most significant fact about Homo erectus is A) They were the first humans to use fire. Homo erectus demonstrated a range of behaviors that were advanced for their time, which includes what many paleoarchaeologists consider a significant milestone in human evolution: the use of fire. Archaeological evidence suggests that Homo erectus was using fire as early as around 1.7-2.0 million years ago, with sites such as Zhoukoudian, China, providing ancient hearths, charcoal, and charred animal bones as proof of this behavior.
This use of fire is notable as it provided warmth, cooked food, and allowed Homo erectus to adapt to various environments, aiding in their survival and expansion out of Africa. Their adaptations also included relatively sophisticated stone tools, cooperation in hunting and foraging, care for the sick and elderly, and possibly rudimentary forms of vocal communication.
Unlike B) skilled cave painters, C) the earliest hominids, or D) developers of complex written language, Homo erectus is not known for these attributes. The earliest evidence of cave painting is attributed to later human species, Homo habilis is often considered an earlier member of our genus, and complex written language developed much later in human history.