I would like to point out that relative components of ancient
diets can be estimated utilizing stable carbon isotopic analysis (i.e.
the 13C/12C ratio).    13C/12C analysis has been used to determine
presumed dietary intake of Australopithecus robustus from 1.8 -1.0
million years ago (1).    The stable carbon isotope ratio (13C/12C)
distinguishes the relative proportions of plants utilizing either the C3
or C4 photosynthetic pathways.   During photosynthesis, C3 plants fix
CO2 into a 3 carbon molecule, while C4 plants fix CO2 into a 4 carbon
molecule.   C3 plants tend to have lower 13C/12C ratios than do C4
plants because 13C (the heavier isotope) is not as readily incorporated
into the tissues of these plants as C4 plants.    Grasses are almost
exclusively C4 plants whereas trees, shrubs and forbs are more generally
C3 plants.    The carbon isotopes (13C and 12C) from plants are
incorporated into the bones and teeth of the animals who consume these
plants.    Grass eating herbivores and the carnivores feeding on them
can then be identified by the higher C13/C12 ratio they maintain in
their bones and teeth.    Lee-Thorp  et al.'s data (1) suggest
Australopithecus robustus consumed a mixed diet containing both C3 and
C4 foods.
        Although, the interpretation is more difficult, strontium
calcium ratios (Sr/Ca) have also been used to estimate dietary
components of ancient diets (2).

        I would like to respond to Steve Meyers comments regarding the
fat level in the paleolithic diet.   As I have mentioned in a previous
post, there is considerable controversy regarding the macronutrient
(PRO/FAT/CHO %) content of pre-agricultural diets.   Clearly, there was
no single "paleolithic diet" and its macronutrient content varied
according to latitude, season and local environmental conditions.   Boyd
Eaton's widely quoted estimate (3) suggests a breakdown of  37% protein,
41% carbohydrate and 22% fat.    This is based upon an estimation of 65%
of derived calories emanating from plant foods and 35% of total calories
emanating from animal foods.    Boyd used Richard's Lee analysis of the
Ethnographic Atlas (4) to arrive at the 65/35 ratio; however Carole
Ember (5) has pointed out that Lee incorrectly tabulated the data and
that in 77% of the societies examined in the Atlas, plant derived foods
represented less than 50% of the calories.    Carefully studied recent
hunter-gatherer societies (Hiwi, Inuit, Ache, Pygmy, !Kung) show a mean
value for the calories derived from animal foods to be 59% (6).   If one
throws out the high value for the Inuit (96% animal food) and the low
value for the !Kung (33%), the value would show that 56% of the average
hunter-gatherer diet was derived from animal foods.    Thus, the average
macronutrient breakdown would probably show a slightly lower CHO % and
slighly higher protein intake when compared to Boyd's estimate.   If
fatty portions of the animal being consumed were preferentially eaten
and lean not consumed, then the fat % could have been significantly
higher.   This clearly would have had to be true for populations living
in northern latitudes wherein the plant food intake would have been
seasonally restricted or eliminated.   In northern latitudes wherein no
plant foods were consumed, expecially during winter months, the dietary
intake was solely reliant upon animal protein and fat.    Speth (7) has
pointed out that the maximal protein intake cannot constitute more than
50% of total calories (when there is no CHO available) and probably
cannot exceed 35% for long periods of time unless CHO is available.
High dietary protein induces diarhea, lethargy and eventual death and
was called "rabbit starvation" by early trappers, explorers and others
forced to eat only lean meat.   The famous Stefansson experiment at
Bellevue Hospital (utilizing an all meat diet) showed that when only
meat and fat were available, self selected diets contained an 80% fat/
20% protein mix.
        Although many of the animals that were hunted by paleolithic
humans have become extinct and we will never know the total carcass
lipid content, many prey animals survived to modern times.   Cave
drawings as well as taphonomical analyses of human occupation sites
indicate animals such as ibex, horse, european elk, deer and other
cervids were widely hunted.    Data from our laboratory as well as data
presented by Speth and colleagues (7) shows that cervid total body fat
content can range from 6 to as high as 15% .    It is quite likely that
large northern pleistocene mammals may have had similar if not greater
values.   Remember that there is significant seasonal variation in these
numbers and certain African ruminants have been reported to have total
body fat percentages of less than 1%, which clearly must approach
physiological limits.   Average body fat % of wild ruminants  tend to be
higher and 4-6% seems to be a pretty good overall estimate, based upon
the few whole body analyses reported in the literature (7).

                                REFERENCES

1.      Lee-Thorp JA et al.  Diet of Australopithecus robustus at
Swartkrans from  stable carbon isotopic analysis.  J Hum Evol
1994;27:361-72.
2.      Sillen A et al.  Strontium calcium ratios and strontium isotopic
ratios of Australopithecus robustus and Homo sp. from Swartkrans.  J Hum
Evol 1995;28:277-85.
3.      Eaton SB et al.  Paleolithic nutrition revisited: A twelve year
retrospective on its nature and implications. Eur J Clin Nutr
1997;51:207-16.
4.      Lee RB.  What hunters do for a living, or how to make out on
scarce resources. In Lee RB, DeVore I, (eds). Man the Hunter. Chicago:
Aldine, 1968:30-48.
5.      Ember CR.  Myths about hunter gatherers. Ethnology
1978;17:439-48.
6.      Leonard WR et al.  Evolutionary perspectives on human nutrition:
the influence of brain and boyd size on diet and metabolism. Am J Hum
Biol 1994;6:77-88.
7.      Speth JD et al.  Energy source, protein metabolism, and
hunter-gatherer subsistence strategies. J Anthropological Archaeology
1983;2:1-31.