I'm sure you've noticed how some elephants look different. Sometimes they are very large, with wide flowing ears and a dominating back, whereas others are slender with small features. No, this can't be chalked up to diet, millions of years of environmental conditions shaping these species into their modern form, yes.
But you're right. Elephants can look very different because African and Asian elephants are very different. In fact, their genetic differences are so great they cannot interbreed. A successful birth has only happened once, and unfortunately Motty died just two weeks after it's birth despite intensive care.
African elephants weight 4,000-7,000 kg (8,800-15,400 lbs) where Asian elephants weight 3,000-6,000 kg (6,600-13,200 lbs). African elephants are generally taller 3-4 meters (10-13 feet), have more wrinkled skin, bigger ears that reach up over the neck, have a concave back and have two fingers on their trunks. Asian elephants are 2-3.5 meters tall (6.5-11 feet), smoother skin, smaller ears and convex back, and females have rudimentary tusks or no tusks at all!