More species of antelope are native to Africa than to any other continent, almost exclusively in savannahs, with 20-35 species co-occurring over much of East Africa. Because savannah habitat in Africa has expanded and contracted five times over the last three million years, and the fossil record indicates this is when most extant species evolved, it is believed that isolation in refugia during contractions was a major driver of this diversification. Other species occur in Asia: the Arabian Peninsula is home to the Arabian oryx and Dorcas gazelle. India is home to the nilgai, chinkara, blackbuck, Tibetan antelope, and four-horned antelope, while Russia and Central Asia have the Tibetan antelope, and saiga.