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The relationship of evolution with diet and environment can provide insights into modern disease. Fossil evidence shows apes, and early human ancestors were fruit eaters living in environments with strongly seasonal climates. Rapid cooling at the end of the Middle Miocene (15–12 Ma: millions of years ago) increased seasonality in Africa and Europe, and ape survival may be linked with a mutation in uric acid metabolism. Climate stabilized in the later Miocene and Pliocene (12–5 Ma), and fossil apes and early hominins were both adapted for life on ground and in trees. Around 2.5 Ma, early species of Homo introduced more animal products into their diet, and this coincided with developing bipedalism, stone tool technology and increase in brain size. Early species of Homo such as Homo habilis still lived in woodland habitats, and the major habitat shift in human evolution occurred at 1.8 Ma with the origin of Homo erectus. Homo erectus had increased body size, greater hunting skills, a diet rich in meat, control of fire and understanding about cooking food, and moved from woodland to savannah. Group size may also have increased at the same time, facilitating the transmission of knowledge from one generation to the next. The earliest fossils of Homo sapiens appeared about 300 kyr, but they had separated from Neanderthals by 480 kyr or earlier. Their diet shifted towards grain-based foods about 100 kyr ago, and settled agriculture developed about 10 kyr ago. This pattern remains for many populations to this day and provides important insights into current burden of lifestyle diseases.

Graphical Abstract
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Content List – This is an article from the symposium: “Bioinspirational medicine”.

Human evolution is strongly influenced by changes in the environment and diet. Our basic tenet is that understanding of modern diseases can be aided by insights from the past, and that knowledge of evolutionary processes and our interactions with the environment may provide insights into the challenges we face as a species as we progress through changing environments that we are, in part, driving. The approach we will take to understand human dietary evolution will be to evaluate environment and diet as they relate in time from fossil apes to modern humans.

The evolution of humans from ancestral apes, to hominins (members of the human lineage) to modern Homo sapiens can be evaluated in part by evaluating the fossil record as it relates to changes in the environment and diet. Fruit is the primary diet of apes and early hominins, and as it is dispersed in space and time, this requires good memory and knowledge of location (Fig. 1). Secondly, the collection of dispersed food items requires the necessary locomotor skills, important in the case of hominins as they converted from 4-legged walking to two legs. Thirdly, hands are used in the preparation of food in hominins, as in most primates, and the human hand changed little from the morphology present in many fossil apes. Fourthly, mastication of food is related to morphologies of the teeth and jaws, and the enlarged teeth with thick enamel in later Miocene fossil apes and Pliocene and early Pleistocene hominins is a function of their coarse or hard-object diets. Finally, digestion of food and storage of energy is based on the concurrence of genetic and metabolic factors.

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Figure 1
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Five stages in feeding process in human evolutionary history 4.
Fossil apes were frugivorous and both arboreal and terrestrial
The earliest fossil apes emerged in Africa during the early Miocene, approximately 25–18 Ma. These apes represented a marked advance over prior primates and were larger (three to four feet long and weighing 10–60 kg) and with a bigger cranial capacity. These early fossil apes had a gracile skull, low alveolar prognathism, and relatively small teeth. They were pronograde tree-climbers. They have been found associated with both tropical rain forest and tropical woodland environments 1-5 and appear to have been mainly fruit eaters 4 and arboreal within these habitats 5.

Evidence for later fossil apes, 16–8 Ma, is that most known species were associated with deciduous woodlands, both tropical and subtropical, and no evidence of rain forest associations has yet been found. Woodlands differ from tropical forest in that they have single tree canopies, making it difficult if not impossible for animals bigger than squirrels to move from tree to tree without coming to the ground 6. Fossil apes from this period have both arboreal and terrestrial adaptations 7, 8. The woodlands were seasonal, losing their leaves in the off-season, either cold or dry, with most plant species fruiting only once a year 9.

At the beginning of the Middle Miocene, at about 16–15 Ma, there was an increase in global temperature, and at this time, the earliest migration of fossil apes out of Africa reached Turkey and Western Europe. They are associated with subtropical, summer rainfall woodlands, for example at Pašalar, Turkey 10. Later species, probably from a separate migration (see below), are associated with subtropical deciduous woodlands in Spain and Hungary 11, and later still with mixtures of deciduous coniferous woodlands and sclerophyllous evergreen woodlands 12-15. The earliest known hominins at 5-4Ma also lived in tropical deciduous woodland 16-18, and the evidence suggests that this habitat did not differ to any significant degree from that of later Miocene apes.

Shortly after the arrival of apes in Europe, global temperatures dropped sharply, marking a period of aridification and falling temperatures. In Africa, the cooler and more seasonal climate would have had the effect of contraction of equatorial forest and increasing seasonality in woodland habitats, and fossil apes are found not in forest but in seasonal woodland habitats. In Eurasia, the cooling resulted in an increasingly seasonal world in which dry/cold seasons were more extreme and longer 19. As a consequence, fruits that had been the primary food for apes, became hard to find during the cooler months. Evidence for intermittent (likely seasonal) starvation has been found at Pašalar in Turkey 20, and all ape colonies receded to small regions (refugia) until complete extinction occurred in Europe and Asia, approximately 8 Ma. Nevertheless, there is some evidence, based on the fossil record, that some of the European apes may have migrated back to Africa during this time 20-25.