The bizarre-looking bald-headed uakari (Cacajao calvus) has a bright crimson bald face. For South American primates they have particularly short tails and broad, flat faces. Four different subspecies are recognised and these exhibit different coat colourations, ranging from the pale orange/white coat of the white bald-headed uakari (Cacajao calvus calvus) to the red coat and pale shoulders of the red bald-headed uakari (C. c. rubicundus). C. c. ucayalii has a reddish-golden coat with black markings on the upper surface of the tail, whilst C. c. novaesi has a more orange tone with pale-coloured shoulders. Malaria is an important disease in some parts of the Amazon rainforest and it is thought that these monkeys may have evolved bright red faces as a symbol of a healthy individual; monkeys who have contracted the disease are noticeably paler and are not chosen as sexual partners as they do not have the desired natural immunity to malaria.