The God-Emperor's Inquisition
Superficially, the Eldar appear very similar to humans in their anatomy, though they are generally taller, faster, thinner, more lithe of limb and slim of face with sharp features and pointed ears. The Eldar possess essentially the same appearance as the elves of classic high fantasy literature. The Eldar are quite long-lived by human standards, and most will live for more than a thousand standard years unless they die from accident or disease. As a species, the Eldar have a universally high level of psychic ability, which also serves as the foundation of their technology, though a side-effect of this neurological make-up is that an Eldar experiences emotion, both pleasant and painful, far more intensely than any human being. The Eldar that actively cultivate their psychic potential seem to exhibit a much-extended lifespan as well, one proportional to their prowess. In this way the leaders and Seers of the Eldar may live for several thousand standard years. One matter of note is that the Eldar have sometimes referred to humans as “mammals” typically with a derogatory label in the Eldar Lexicon like “the Mon-Keigh”, implying that for their part, the Eldar evolved from something else, something more advanced than the primates that are the ancestors of Mankind.