Over 89 species from 12 of the 17 families of of primates eat meat. These 89 species are scattered all over the world. Birds, including their eggs, are the most common primate prey, followed by reptiles, amphibians, mammals and even fish. Chimpanzees are the kings of variety, with 45 different vertebrate species appearing in their diets. 

But why to eat meat? Primates seem to be better off covering their calorie and protein needs by eating plants and invertebrates than by hunting. 

Most primates feed on meat sporadically, and it represents less than the 1 percent of the diet in almost all 89 species. There is no evidence that primates rely on meat for energy when other resources are scarce. The most likely explanation for meat-eating by primates at present is that meat provides micronutrients, such as vitamins and minerals, that are found in plants in only very small amounts. 

Human meat-eating is quite different from that of other primates. Meat is a key source of energy for many of us modern humans and our ancestors. And while other primates feed on prey much smaller than themselves, we hunt animals larger than ourselves. 

Throwing-weapons and other hunting tools play a considerable role in achieving this human feat. Some chimpanzees and capuchin monkeys do use tools like sticks for hunting. However, big game hunting from a distance seems to be exclusive to the human lineage.

"Peinar canas" es una expresión que usamos para indicar que alguien tiene una edad avanzada. Para nosotros, los humanos, este dicho es muy preciso ya que, por regla general, cuantos más años cumplimos, más canas acumulamos. En la primera mitad de nuestras vidas pueden aparecer algunos cabellos blancos. Sin embargo, es una vez que llegamos a la mediana edad cuando nuestro cabello puede perder su color original por completo. Por tanto, las canas son un buen indicador de la edad en los seres humanos. 

Pero, ¿es este el caso de nuestros parientes evolutivos más cercanos? ¿Puedes estimar la edad de un chimpancé por la cantidad de canas de su cabeza?

Para averiguarlo, los científicos fotografiaron las caras de chimpancés de diferentes edades e hicieron que 152 observadores humanos contaran la cantidad de canas en cada foto.

Al analizar los datos, los investigadores descubrieron que las canas en los chimpancés funcionan de manera diferente que en los humanos. En los chimpancés, el cabello puede empezar a volverse gris al principio de la vida, pero una vez que llegan a la mediana edad, el proceso se detiene y casi no aparecen nuevas canas. Vamos, todo lo contrario de lo que ocurre en humanos. Además, hay mucha variación entre individuos de chimpancé; puede haber un chimpancé de 5 años con más canas que uno de 50 años. Por tanto, no se puede saber la edad de un chimpancé por sus canas.

No está claro cuál podría ser la utilidad biológica de esta diferencia, pero indica que el encanecimiento no está necesariamente vinculado al proceso de envejecimiento en mamíferos. 

To find out, a group of anthropologists took pictures of the faces of chimpanzees of different ages. They recruited 152 human observers, who were unfamiliar with these chimpanzees, and asked them to score the number of gray hairs they saw. 

The researchers discovered that hair graying in chimpanzees occurs at different times than it does in humans. Chimpanzees' hair becomes more gray from the time they are young up until the middle of their lives, but then the graying tends to stop. The opposite is true for humans, where graying is more striking from midlife on. They also found that a lot of variation between individuals, meaning that a 5-year-old chimp might have grayer hair than a 50-year-old ape. So, you cannot tell a chimp's age by the gray hairs on their heads!

It is unclear what the purpose of this difference might be, but it does indicate that going gray is not a reliable measure of age in mammals.