From Michael Eades' latest blog post:  
http://www.proteinpower.com/drmike/low-carb-diets/are-we-meat-eaters-or-vegetarians-part-iii/#more-4681

A little over two years ago I wrote a couple of posts arguing that we  
cut our ancestral teeth on meat, and that contrary to all the  
vegetarian blather about colon length, tooth structure, etc., the  
archeological and anthropological convincingly demonstrates we were  
descended from meat eaters, not vegetarians.  (Click here and here for  
those posts.) A couple of recent developments have now inspired me to  
write a third.

First, I noticed in both talking with people at the Ancestral Health  
Symposium last August and attending a number of the talks that many  
followers of their own version of the ancestral diet are dismayingly  
including more and more carbohydrates.  And recommending more to their  
followers.

When MD and I wrote Protein Power in the mid 1990s, we used the  
Paleolithic diet as an argument for the efficacy of the low-carb diet.  
  If pre-agricultural man evolved in a milieu devoid of  
carbohydrate-dense foods, we posited, then natural selection should  
have culled those who didn?t thrive on such fare, leaving us, the  
descendants, powered by metabolic processes that performed better on  
protein and fat substrates.  If the rampant obesity and diabetes (we  
just thought it was rampant then) was a consequence of a diet we  
weren?t designed for, then switching to one that better suited us  
metabolically should produce substantial changes to the good.  Which  
it undeniably does.

I can?t help but recall the great quote by Dr. Blake Donaldson, who  
changed the complexion of his practice in New York after spending some  
time with Vilhjalmur Stefansson.  Wrote Dr. Donaldson in Strong  
Medicine, his book about an almost all meat diet:

During the millions of years that our ancestors lived by hunting,  
every weakling who could not maintain perfect health on fresh meat and  
water was bred out.

Now, it seems, many who have taken to the Paleo diet have started to  
drift from the Paleo-is-basically-low-carb paradigm into the  
Paleo-is-anything-that-isn?t-Neolithic paradigm.  And although  
Neolithic man grew all sorts of crops, most Paleo dieters consider  
only grains to be truly Neolithic foods.  Some Paleo dieters take it a  
step further and argue that since pre-agricultural man couldn?t have  
domesticated animals (other than perhaps canids of some sort), then he  
couldn?t have eaten dairy products.  So, those Paleo purists avoid  
grain and dairy products.  Both the dairy and non-dairy Paleo dieters,  
however, are starting to include larger amounts of carbohydrates ?  
primarily starch ? into their diets on the presumption that Paleo man  
would have eaten it.

I have no doubt that Paleo man would have been face down in a box of  
donuts had he been given the opportunity.  But he wasn?t.  Nor was he  
often presented with the opportunity to indulge in a carb fest  
composed of high-starch fruits and vegetables. Maybe in the fall when  
the fruit ripened (if he could beat the birds and bugs to it), but not  
much of a chance during the rest of the year.
(I am aware that Denise Minger put up a post not too long ago showing  
all the high-starch, high-sugar tropical fruits available in tropical  
areas, intimating that early man must have consumed these and,  
therefore, should have evolved to do okay on high-carb diets.  Problem  
with this reasoning is that archaic homo sapiens migrated out of  
tropical areas anywhere from 60,000 to 150,000 years ago and went  
through the crucible of natural selection in other less fruit-laden  
climes.  People of European descent certainly had ancestors who could  
not avail themselves of tropical fruits at any time.)

The second event driving me to write is a line out of a guest post on  
Richard Nikoley?s Free the Animal blog by Darrin Carlson titled ?The  
Five Failings of Paleo.?  In Mr. Carlson?s own words, here is Paleo  
Fail #1:

We Don?t REALLY Know What Our Ancestors Ate. [Bold and caps in the original.]

I disagree for a couple of reasons.  First, we can be pretty certain  
what our European ancestors didn?t eat.  They didn?t eat dwarf wheat,  
Red Delicious apples, bananas, Bartlett pears or any other hybridized  
or tropical fruits commonly available today. As far as we know, there  
were no Paleo Luther Burbanks grafting and hybridizing plants to make  
them bigger and sweeter.  Our predecessors would have eaten whatever  
plant foods were at hand, which is pretty much what you still find if  
you go out in the woods today. They would have had to battle the birds  
and other wildlife to get to these fruits, and would have had them  
available only seasonally.

The second reason I disagree is alluded to in a way by Mr. Carlson in  
his explanation of Fail #1: Said he:

We have yet to find a magic phone booth that will transfer us back  
through time?Bill and Ted notwithstanding?to directly observe how our  
great-times-450-grandparents lived.

Actually we do have such a ?magic phone booth? available to us, or at  
least to those of us who know how to use it.  It?s an isotope ratio  
mass spectrometer, and its use has been refined over the past 30-40  
years to allow us to peer back in time and calculate what our  
ancestors ate.

I learned about this ?magic phone booth? in the fall of 2000 in  
Hamburg, Germany where MD and I attended a great conference titled  
Meat and Nutrition.  After the last talk, on a cold, dreary, foggy,  
drizzly afternoon, MD, Loren Cordain and I lit out to  make a  
pilgrimage to Indra and the Kaiserkeller, the dives where the Beatles  
had gotten their start in the early 1960s.  We asked Michael Richards,  
a professor at the University of Bradford to join us.  On the first  
morning of the meeting, Michael had given a riveting talk on the use  
of stable isotopes to determine the diet of early man, and I wanted to  
find out more.

After roaming the Beatles early haunts, we decamped to a Hamburg  
coffee house to get warm.  I asked many questions about the stable  
isotope methodology and have followed the growing literature on it  
since.  Michael has turned into an academic superstar and is now at  
the prestigious Max Planck Institute for Evolutionary Anthropology in  
Leipzig, Germany, where he continues to publish his work on the  
isotopic analysis of the diet of early man.

Let?s take a look at the ?magic phone booth? of stable isotope  
analysis and see what it shows.  The whole notion is fairly complex so  
I?m torn between making its science simple enough for Homer Simpson to  
understand, which really doesn?t do the technique justice, or making  
it unnecessarily difficult. I?m shooting for something in between.

As most everyone knows, atoms are composed of protons, electrons and  
neutrons.  The number of protons gives an element its atomic number.   
A given element always has the same number of protons but can have  
varying numbers of neutrons.  Carbon, for example, has six protons  
(and an atomic number of 6).  But the carbon atom can have 6, 7 or 8  
neutrons.  All three versions are still carbon, but the atoms vary by  
the number of neutrons.  These different versions are called isotopes,  
so basically isotopes are atoms of the same element with the same  
number of protons but differing numbers of neutrons.  The atomic mass  
of an atom is determined by the number of protons and neutrons it  
contains, so although carbon always carries the atomic number of 6,  
carbon has three different atomic masses: 12C, 13C and 14C.

Carbons with an atomic mass of 12 and 13 (12C, 13C) are stable whereas  
14C (pronounced carbon 14) disintegrates radioactively over time.   
This radioactive decay is what allows scientists to determine the age  
of organic materials up to about 40,000 years old. The discovery of  
natural radioactivity of 14C and its usefulness in determining age  
garnered Willard Libby the 1960 Nobel Prize in Chemistry.  Although  
the unstable isotopes such as 14C have their uses, we are concerned  
here with the stable isotopes.  Primarily 12C and 13C and 14N and 15N  
(nitrogen 14 and 15).  From these four stable isotopes, we can learn a  
lot about the diet of early man.

Nuclear weapons started adding 14C into the atmosphere in the mid  
1900s, so the average ratio of 12C, 13C and 14C have change slightly.   
  Since 12C and 13C are stable, there has been virtually no change in  
the ratio between them over time.  But the ratio of the two has been  
found to differ from one carbon-containing material to another.  For  
instance, carbon dioxide generated from marine limestone contains more  
13C than does carbon dioxide generated from burning wood.  In general,  
marine sources have greater amounts of 13C than do terrestrial sources.

Just to make it a little more complex, when researchers run samples  
through a mass spectrometer to determine the 13C/12C ratio, this ratio  
is compared to an agreed standard.  Then the difference between the  
sample and the standard is called the relative 13C content, which is  
designated by ?13C and measured in parts per thousand. (?)  So if the  
sample has a ratio less than the standard by 5 parts per thousand, it  
is defined as having a ?13C value of ?5?.
Don?t worry about all the above ? just remember when you see ?13C from  
now on, it refers to the ratio of 13C to 12C.  Don?t despair.  It will  
be easier as we go along.

Of the dry weight of bone, a little over 25 percent is collagen, and  
it is collagen that is the tissue of choice for stable isotope  
analysis.  Virtually all of the carbon and nitrogen in collagen comes  
from protein, and since most protein in the human body ultimately  
comes from protein in the diet, the carbon and nitrogen isotopes in  
the collagen reflect the protein sources in the diet.  And since the  
stable isotope composition of collagen turns over very slowly, the  
ratios of carbon and nitrogen stable isotopes reflect diet over about  
an eight to ten year period.

Stable isotopes of both carbon and nitrogen occur in varying  
proportions in different foods, and these proportions are passed along  
to the animals, including humans, that ate these foods.  By knowing  
the proportions of the stable isotopes in various foods, we can  
determine these foods by analyzing the stable isotopes in human  
collagen.

Researchers are able to extract valuable data from the collagen of  
ancient bones.  Unfortunately ancient bones are not thick on the  
ground, and since a part of the bone has to be destroyed to perform  
the stable isotope analysis, these analyses are not done by the  
thousands.  Each time a skeleton or group of skeletons is unearthed,  
Michael Richards and other stable isotope researchers try to snare a  
little piece of bone and go at it with the mass spectrometer.  This  
kind of work has been done for several decades now, and the results ?  
though painstakingly obtained one specimen at a time ? are  
accumulating, and there is now a fairly substantial body of data.  And  
this data is remarkably uniform in what it shows of the dietary habits  
of our ancient European ancestors.

The ?13C and ?15N figures reveal different information about the diet  
of Paleo man.  Since the 13C isotope is found in greater quantities in  
the marine environment than in the terrestrial, a larger ?13C  
indicates a diet higher in seafood protein whereas a lower ?13C is  
associated with a diet composed primarily of protein foods from the  
land.  Researchers have accumulated considerable data on the ?13C of  
seals and other such animals that spend their lives in the oceans  
consuming other marine life to compare with the data gleaned from  
bones of animals living on the land far from the sea.  By noting how  
the ?13C from ancient human bone compares to these extremes determines  
whether the human dined on protein from terrestrial or marine sources  
of from a combination of the two.

The ?15N tells a different story.  ?15N basically tells us where an  
animal or human is on the food chain.  Basic plant foods maintain a  
fairly constant ?15N value.  When animals, typically herbivores, eat  
these plant foods, the stable N isotope in the plant food tends to  
concentrate by anywhere from 5-8 percent in the collagen of the  
animal.  So if the collagen of an animal is found to have, say, a 7  
percent greater ?15N than the local flora, one can say the animal was  
an herbivore.  Animals that are known herbivores, when analyzed, fit  
this spectrum.

Any animal, including man, that dines on herbivores will have collagen  
sporting a ?15N that is about 7 percent greater than that found in the  
herbivores that are the meal, a fact confirmed by stable isotope  
analysis of known carnivores.  A super carnivore (for lack of a better  
name) that dines on other carnivores and herbivores would have an even  
greater ?15N level.

So, ?15N pinpoints us on the food chain while ?13C tells us whether  
the protein we eat is surf or turf or both.

Now that we have a full understanding of the ?magic phone booth? of  
stable isotope analysis, let?s take a look at what the data show.

The data taken as a whole show the following:

Early man was a high-level carnivore. (As was his distant relative the  
Neanderthal, who lived contemporaneously with ancient man in Europe.)   
A higher-level carnivore, in fact, than foxes, wolves and other known  
carnivores.  The earliest anatomically modern humans got most of their  
protein from animals of terrestrial origin.  As time passed and the  
populations of large game thinned due to heavy hunting by both humans  
and Neanderthals, the human position on the food chain didn?t change,  
but sources of protein changed from all terrestrial to more and more  
marine (which includes fresh water fish, mussels, clams, etc., all of  
which have a similar ?13C as animals from the ocean).  Irrespective of  
whether the protein came from the land or the sea, early man occupied  
a super-carnivore niche in pre-agricultural days.