The seeds are highly toxic but the compounds responsible are not soluble in the oil. See the diagram on page 342. Castor bean probably grew in both Asia and Africa when it was domesticated. Seeds have been found in Egyptian tombs at least 6000 years old. The oil was probably used in medicine and as a lamp oil.
Castor oil is also a precursor for plastics.
Today most castor oil is used for soaps, paints, and Turkey red oil. It is also used widely as a lubricant. The press cake is too toxic for any use except fertilizer. Palm and palm kernel oils. There is also a comparable Asian species.