65,000,000 to 50,000,000 B.C.: The first primates, resembling today's mouse lemurs, bush-babies, and tarsiers, weighing in at 2 lbs. or less, and eating a largely insectivorous diet.[8]

50,000,000 to 30,000,000 B.C.: A gradual shift in diet for these primates to mostly frugivorous in the middle of this period to mostly herbivorous towards the end of it, but with considerable variance between specific primate species as to lesser items in the diet, such as insects, meat, and other plant foods.[9]

30,000,000 to 10,000,000 B.C.: Fairly stable persistence of above dietary pattern.[10]

Approx. 10,000,000 to 7,000,000 B.C.: Last common primate ancestor of both humans and the modern ape family.[11]

Approx. 7,000,000 to 5,000,000 B.C.: After the end of the previous period, a fork occurs branching into separate primate lines, including humans.[12] The most recent DNA evidence shows that humans are closely related to both gorillas and chimpanzees, but most closely to the chimp.[13] Most paleoanthropologists believe that after the split, flesh foods began to assume a greater role in the human side of the primate family at this time.[14]

Approx. 4,500,000 B.C.: First known hominid (proto-human) from fossil remains, known as Ardipithecus ramidus--literally translating as "root ape" for its position as the very first known hominid, which may not yet have been fully bipedal (walking upright on two legs). Anatomy and dentition (teeth) are very suggestive of a form similar to that of modern chimpanzees.[15]

Approx. 3,700,000 B.C.: First fully upright bipedal hominid, Australopithecus afarensis (meaning "southern ape," for the initial discovery in southern Africa), about 4 feet tall, first known popularly from the famous "Lucy" skeleton.[16]

3,000,000 to 2,000,000 B.C.: Australopithecus line diverges into sub-lines,[17] one of which will eventually give rise to Homo sapiens (modern man). It appears that the environmental impetus for this "adaptive radiation" into different species was a changing global climate between 2.5 and 2 million years ago driven by glaciation in the polar regions.[18] The climatic repercussions in Africa resulted in a breakup of the formerly extensively forested habitat into a "mosaic" of forest interspersed with savanna (grassland). This put stress on many species to adapt to differing conditions and availability of foodstuffs.[19] The different Australopithecus lineages, thus, ate somewhat differing diets, ranging from more herbivorous (meaning high in plant matter) to more frugivorous (higher in soft and/or hard fruits than in other plant parts).

There is still some debate as to which Australopithecus lineage modern humans ultimately descended from, but recent evidence based on strontium/calcium ratios in bone, plus teeth microwear studies, show that whatever the lineage, some meat was eaten in addition to the plant foods and fruits which were the staples.[20]

2,300,000 to 1,500,000 B.C.: Appearance of the first "true humans" (signified by the genus Homo), known as Homo habilis ("handy man")--so named because of the appearance of stone tools and cultures at this time. These gatherer-hunters were between 4 and 5 feet in height, weighed between 40 to 100 pounds, and still retained tree-climbing adaptations (such as curved finger bones)[21] while subsisting on wild plant foods and scavenging and/or hunting meat. (The evidence for flesh consumption based on cut-marks on animal bones, as well as use of hammerstones to smash them for the marrow inside, dates to this period.[22]) It is thought that they lived in small groups like modern hunter-gatherers but that the social structure would have been more like that of chimpanzees.[23]

The main controversy about this time period by paleoanthropologists is not whether Homo habilis consumed flesh (which is well established) but whether the flesh they consumed was primarily obtained by scavenging kills made by other predators or by hunting.[24] (The latter would indicate a more developed culture, the former a more primitive one.) While meat was becoming a more important part of the diet at this time, based on the fact that the diet of modern hunter-gatherers--with their considerably advanced tool set--has not been known to exceed 40% meat in tropical habitats* like habilis evolved in, we can safely assume that the meat in habilis' diet would have been substantially less than that.[25]

1,700,000 to 230,000 B.C.: Evolution of Homo habilis into the "erectines,"* a range of human species often collectively referred to as Homo erectus, after the most well-known variant. Similar in height to modern humans (5-6 feet) but stockier with a smaller brain, hunting activity increased over habilis, so that meat in the diet assumed greater importance. Teeth microwear studies of erectus specimens have indicated harsh wear patterns typical of meat-eating animals like the hyena.[26] No text I have yet read ventures any sort of percentage figure from this time period, but it is commonly acknowledged that plants still made up the largest portion of the subsistence.* More typically human social structures made their appearance with the erectines as well.[27]

The erectines were the first human ancestor to control and use fire. It is thought that perhaps because of this, but more importantly because of other converging factors--such as increased hunting and technological sophistication with tools--that about 900,000 years ago in response to another peak of glacial activity and global cooling (which broke up the tropical landscape further into an even patchier mosaic), the erectines were forced to adapt to an increasingly varied savanna/forest environment by being able to alternate opportunistically between vegetable and animal foods to survive, and/or move around nomadically.[28]

For whatever reasons, it was also around this time (dated to approx. 700,000 years ago) that a significant increase in large land animals occurred in Europe (elephants, hoofed animals, hippopotamuses, and predators of the big-cat family) as these animals spread from their African home. It is unlikely to have been an accident that the spread of the erectines to the European and Asian continent during and after this timeframe coincides with this increase in game as well, as they probably followed them.[29]

Because of the considerably harsher conditions and seasonal variation in food supply, hunting became more important to bridge the seasonal gaps, as well as the ability to store nonperishable items such as nuts, bulbs, and tubers for the winter when the edible plants withered in the autumn. All of these factors, along with clothing (and also perhaps fire), helped enable colonization of the less hospitable environment. There were also physical changes in response to the colder and darker areas that were inhabited, such as the development of lighter skin color that allowed the sun to penetrate the skin and produce vitamin D, as well as the adaptation of the fat layer and sweat glands to the new climate.*[30]

Erectus finds from northern China 400,000 years ago have indicated an omnivorous diet of meats, wild fruit and berries (including hackberries), plus shoots and tubers, and various other animal foods such as birds and their eggs, insects, reptiles, rats, and large mammals.[31]

500,000 to 200,000 B.C.: Archaic Homo sapiens (our immediate predecessor) appears. These human species, of which there were a number of variants, did not last as long in evolutionary time as previous ones, apparently due simply to the increasingly rapid rate of evolution occurring in the human line at this time. Thus they represent a transitional time after the erectines leading up to modern man, and the later forms are sometimes not treated separately from the earliest modern forms of true Homo sapiens.[32]

150,000 to 120,000 B.C.: Homo sapiens neanderthalensis--or the Neanderthals--begin appearing in Europe, reaching a height between 90,000 and 35,000 years ago before becoming extinct. It is now well accepted that the Neanderthals were an evolutionary offshoot that met an eventual dead-end (in other words, they were not our ancestors), and that more than likely, both modern Homo sapiens and Neanderthals were sister species descended from a prior common archaic sapiens ancestor.[33]

140,000 to 110,000 B.C.: First appearance of anatomically modern humans (Homo sapiens).[34] The last Ice Age also dates from this period--stretching from 115,000 to 10,000 years ago. Thus it was in this context, which included harsh and rapid climatic changes, that our most recent ancestors had to flexibly adapt their eating and subsistence.[35] (Climatic shifts necessitating adaptations were also experienced in tropical regions, though to a lesser degree.[36]) It may therefore be significant that fire, though discovered earlier, came into widespread use around this same time[37] corresponding with the advent of modern human beings. Its use may in fact be a defining characteristic of modern humans[38] and their mode of subsistence. (I'll discuss the timescale of fire and cooking at more length later.)

130,000 to 120,000 B.C.: Some of the earliest evidence for seafoods (molluscs, primarily) in the diet by coastal dwellers appears at this time,[39] although in one isolated location discovered so far, there is evidence going back 300,000 years ago.[40] Common use of seafoods by coastal aborigines becomes evident about 35,000 years ago,[41] but widespread global use in the fossil record is not seen until around 20,000 years ago and since.[42] For the most part, seafoods should probably not be considered a major departure,* however, as the composition of fish, shellfish, and poultry more closely resembles the wild land-game animals many of these same ancestors ate than any other source today except for commercial game farms that attempt to mimic ancient meat.[43]

40,000 to 35,000 B.C.: The first "behaviorally modern" human beings--as seen in the sudden explosion of new forms of stone and bone tools, cave paintings and other artwork, plus elaborate burials and many other quintessentially modern human behaviors. The impetus or origin for this watershed event is still a mystery.[44]

40,000 B.C. to 10-8,000 B.C.: Last period prior to the advent of agriculture in which human beings universally subsisted by hunting and gathering (also known as the "Late Paleolithic"--or "Stone Age"--period). Paleolithic peoples did process some of their foods, but these were simple methods that would have been confined to pounding, grinding, scraping, roasting, and baking.[45]

35,000 B.C. to 15-10,000 B.C.: The Cro-Magnons (fully modern pre-Europeans) thrive in the cold climate of Europe via big-game hunting, with meat consumption rising to as much as 50%* of the diet.[46]

25,000 to 15,000 B.C.: Coldest period of the last Ice Age, during which global temperatures averaged 14°F cooler than they do today[47] (with local variations as much as 59°F lower[48]), with an increasingly arid environment and much more difficult conditions of survival to which plants, animals, and humans all had to adapt.[49] The Eurasian steppes just before and during this time had a maximum annual summer temperature of only 59°F.[50]

Humans in Europe and northern Asia, and later in North America, adapted by increasing their hunting of the large mammals such as mammoths, horses, bison and caribou which flourished on the open grasslands, tundra, and steppes which spread during this period.[51] Storage of vegetable foods that could be consumed during the harsh winters was also exploited. Clothing methods were improved (including needles with eyes) and sturdier shelters developed--the most common being animal hides wrapped around wooden posts, some of which had sunken floors and hearths.[52] In the tropics, large areas became arid. (In South Africa, for instance, the vegetation consisted mostly of shrubs and grass with few fruits.[53])

20,000 B.C. to 9,000 B.C.: Transitional period known as the "Mesolithic," during which the bow-and-arrow appeared,[54] and gazelle, antelope, and deer were being intensively hunted,[55] while at the same time precursor forms of wild plant and game management began to be more intensively practiced. At this time, wild grains, including wheat and barley by 17,000 B.C.--before their domestication--were being gathered and ground into flour as evidenced by the use of mortars-and-pestles in what is now modern-day Israel. By 13,000 B.C. the descendants of these peoples were harvesting wild grains intensely and it was only a small step from there to the development of agriculture.[56] Game management through the burning-off of land to encourage grasslands and the increase of herds became widely practiced during this time as well. In North America, for instance, the western high plains are the only area of the current United States that did not see intensive changes to the land through extensive use of fire.[57]

Also during this time, and probably also for some millennia prior to the Mesolithic (perhaps as early as 45,000 B.C.), ritual and magico-religious sanctions protecting certain wild plants developed, initiating a new symbiotic relationship between people and their food sources that became encoded culturally and constituted the first phase of domestication well prior to actual cultivation. Protections were accorded to certain wild food species (yams being a well-known example) to prevent disruption of their life cycle at periods critical to their growth, so that they could be profitably harvested later.[58] Digging sticks for yams have also been found dating to at least 40,000 B.C.,[59] so these tubers considerably antedated the use of grains in the diet.

Foods known to be gathered during the Mesolithic period in the Middle East were root vegetables, wild pulses (peas, beans, etc.), nuts such as almonds, pistachios, and hazelnuts, as well as fruits such as apples. Seafoods such as fish, crabs, molluscs, and snails also became common during this time.[60]

Approx. 10,000 B.C.: The beginning of the "Neolithic" period, or "Agricultural Revolution," i.e., farming and animal husbandry. The transition to agriculture was made necessary by gradually increasing population pressures due to the success of Homo sapiens' prior hunting and gathering way of life. (Hunting and gathering can support perhaps one person per square 10 miles; Neolithic agriculture 100 times or more that many.[61]) Also, at about the time population pressures were increasing, the last Ice Age ended, and many species of large game became extinct (probably due to a combination of both intensive hunting and disappearance of their habitats when the Ice Age ended).[62] Wild grasses and cereals began flourishing,* making them prime candidates for the staple foods to be domesticated, given our previous familiarity with them.[63] By 9,000 B.C. sheep and goats were being domesticated in the Near East, and cattle and pigs shortly after, while wheat, barley, and legumes were being cultivated somewhat before 7,000 B.C., as were fruits and nuts, while meat consumption fell enormously.[64] By 5,000 B.C. agriculture had spread to all inhabited continents except Australia.[65] During the time since the beginning of the Neolithic, the ratio of plant-to-animal foods in the diet has sharply increased from an average of probably 65%/35%* during Paleolithic times[66] to as high as 90%/10% since the advent of agriculture.[67]

Remains of fossil humans indicate decrease in health status after the Neolithic. In most respects, the changes in diet from hunter-gatherer times to agricultural times have been almost all detrimental, although there is some evidence we'll discuss later indicating that at least some genetic adaptation to the Neolithic has begun taking place in the approximately 10,000 years since it began. With the much heavier reliance on starchy foods that became the staples of the diet, tooth decay, malnutrition, and rates of infectious disease increased dramatically over Paleolithic times, further exacerbated by crowding leading to even higher rates of communicable infections.

Skeletal remains show that height decreased by four inches* from the Late Paleolithic to the early Neolithic, brought about by poorer nutrition, and perhaps also by increased infectious disease causing growth stress, and possibly by some inbreeding in communities that were isolated. Signs of osteoporosis and anemia, which was almost non-existent in pre-Neolithic times, have been frequently noted in skeletal pathologies observed in the Neolithic peoples of the Middle East. It is known that certain kinds of osteoporosis which have been found in these skeletal remains are caused by anemia, and although the causes have not yet been determined exactly, the primary suspect is reduced levels of iron thought to have been caused by the stress of infectious disease rather than dietary deficiency, although the latter remains a possibility.[68]

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