Ancient human ancestors who lived in East Africa between 2.4 million to 1.4 million years ago survived mainly on a diet of tiger nuts, supplemented with grasshoppers and worms, Oxford researchers have found.
The study found that early hominins ate tiger nuts - edible grass bulbs still eaten in parts of the world today - and sought additional nourishment from fruits and invertebrates, like worms and grasshoppers.
Study author Dr Gabriele Macho examined the diet of Paranthropus boisei, nicknamed "Nutcracker Man" because of his big flat molar teeth and powerful jaws, through studying modern-day baboons in Kenya.
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Scholars have debated why this early human relative had such strong jaws, indicating a diet of hard foods like nuts, yet their teeth seemed to be made for consuming soft foods.
Damage to the tooth enamel also indicated they had come into contact with an abrasive substance. Previous research using stable isotope analyses suggests the diet of these homimins comprised C4 plants like grasses and sedges.
However, a debate has raged over whether such high-fibre foods could ever be of sufficiently high quality for a large-brained, medium-sized hominin.
Macho's study found that baboons today eat large quantities of C4 tiger nuts, and this food would have contained sufficiently high amounts of minerals, vitamins, and the fatty acids that would have been particularly important for the hominin brain.
The finding is grounded in existing data that details the diet of year-old baboons in Amboseli National Park in Kenya - a similar environment to that once inhabited by Paranthropus boisei.
Macho's study is based on the assumption that baboons intuitively select food according to their needs. She concluded that the nutritional demands of a hominin would have been quite similar.
Tiger nuts, rich in starches, are highly abrasive in an unheated state. Macho suggested that hominins' teeth suffered abrasion and wear and tear due to these starches.
In order to digest the tiger nuts and allow the enzymes in the saliva to break down the starches, the hominins would need to chew the tiger nuts for a long time.
All this chewing put considerable strain on the jaws and teeth, which explained why "Nutcracker Man" had such a distinctive cranial anatomy, researchers said.
"I believe that the theory - that "Nutcracker Man" lived on large amounts of tiger nuts - helps settle the debate about what our early human ancestor ate," said Macho, from the School of Archaeology at Oxford University.
"On the basis of recent isotope results, these hominins appear to have survived on a diet of C4 foods, which suggests grasses and sedges. Yet these are not high quality foods.
"What this research tells us is that hominins were selective about the part of the grass that they ate, choosing the grass bulbs at the base of the grass blade as the mainstay of their diet," Macho said.
