> wrote in message ...

> ""We think that selection is strongly favouring more copies in populations
> with more starch in the diet," says Dominy. The study is one of the first
> to show that natural selection can lead to an increase in gene copy
> numbers.
>
> If that increase coincided with the dramatic expansion in our ancestor's
> brain size about 1.8 million years ago, that would be the strongest
> possible evidence that roots and tubers, not meat, fuelled our
> intelligence."
>
> Very good, some science at last instead of quibbling. Given the potential
> confounding factors of knowing back 1.8 million years the same authors
> mentioned, how do we know this is any different?
>
> Science proceeds by alternative models over time sorting and sifting until
> a concensus is reached. Where does the above stand today in that
> concensus?

'In summary it appears that underground roots and tubers would make an
important nutritional addition to the diet of Australopithecus, who might have
been able to live exclusively on roots and tubers during short periods of
above-ground food scarcity. Furthermore, the dental and microwear patterns
exhibited by Australopithecus are compatible with the additions of roots to a
chimpanzee-like diet (Hatley and Kappelman, 1980; Grine and Kay, 1988).
They would not have needed additional protein supplement to top-up their
protein intake to safe levels. In addition, the lower fiber values would improve
the quality of their diet. This does not imply that a need to decrease fiber in the
diet was a driving force in the evolution of the hominid diet. However, with the
serendipitous addition of underground storage organs to the Australopithecus
diet and the resulting increase in the nutrient density of the diet, the stage was
set for Homo to further reduce fiber levels and further improving the nutrient
quality of their diet.'
...'
http://www.cast.uark.edu/local/icaes...n/conklin.html

'Theories of Human Evolutionary Trends in Meat Eating and Studies of
Primate Intestinal Tracts
Patrick Pasquet
Centre National de la Recherche Scientifique, France
Claude-Marcel Hladik
Museum d'Histoire Naturelle, France
...
Theories of hominid evolution have postulated that switching to meat eating
permitted an increase in brain size and hence the emergence of modern man.
However, comparative studies of primate intestinal tracts do not support this
hypothesis and it is likely that, while meat assumed a more important role in
hominid diet, it was not responsible for any major evolutionary shift.
....
The adaptive biological significance of meat eating was summarized by Milton
(1999),who came to the conclusion that "the incorporation of animal matter
into the diet played an absolutely essential role in human evolution", otherwise
the arid and seasonal environment likely to have been the cradle of hominids
would not have provided enough protein. The link between a high quality
diet (including animal matter) and the enlargement of the brain (characterizing
hominization) has been highlighted by several authors (Martin, 1983; Foley
and Lee, 1991; Leonard and Robertson, 1997).

In their most quoted paper, the argument of Aiello and Wheeler (1995)
supports this view, proposing the "expensive-tissue hypothesis", related to
the evolutionary forces implied in the increase of hominid brain size. They
focus on the shift to a high-quality diet and corresponding gut adaptation.
A reduced intestinal mass would considerably lower the relative energy cost
and permit disposal of sufficient energy to cover the extra-expenditure of a
larger brain. The main point of Aiello and Wheeler is based on the
relationship between body mass and Basal Metabolic Rate (BMR): the
Kleiber line characterizing the relationship between BMR and body size is
identical for all mammals, including humans. Since maintenance of gut tissue
is as expensive as that of brain tissue, Aiello and Wheeler proposed that gut
reduction compensated for brain increase.

Henneberg et al. (1998), following this point of view, developed further
arguments on the role of meat eating in human evolution. For these authors,
the "quantitative similarity of human gut morphology to guts of carnivorous
mammals" is a strong argument for a human status of "well evolved meat
eater". In fact, one should ask if there is actual evidence of human gut
adaptation to meat eating in the past that would have permitted a
characteristic swing towards carnivorousness.
....
Thus, in humans, a clear-cut adaptation to meat eating would imply that
the gut allometric relationship coincides with that of the "faunivores", with
the lowest absorptive area. This is not supported by the measurements of
human gut size that are plotted in Fig 1, all these measurements being
grouped on the best fit line of the frugivores (Hladik et al., 1999). ..

Returning to the issue of relating increase in brain size to dietary adaptation,
there is obviously no direct relationship. Similarly, Martin (1983) in his
allometric analysis of the evolution of the mammal brain identified four
separate "grades" of relative brain size (Fig. 2) characterized by the slope
of the major axis of the relationship between cranial capacity and body
weight.

Fig.2 Allometric relationships between cranial capacity and body
weight in different categories of primates and insectivorous mammals
SOURCE: R. D. Martin, 1983.

Since each of these "grades" includes species with different diets
(folivorous, frugivorous, carnivorous), there is no clear-cut relationship
between brain size and dietary adaptation. It is thus likely that a
compensatory energetic reduction that allows the functioning of the large
brain of Homo (with respect to Kleiber's law) may affect all body parts,
rather than being exclusively focused on gut tissue.

DISCUSSION: DIET AND HOMINIZATION

Most forest primates have a frugivorous diet, with a supplement of protein
provided either by young vegetable shoots and leaves, or by animal matter
(mostly invertebrates). This is a most flexible dietary adaptation that allows
them to switch between the various categories of food items available in
different habitats throughout the seasons of the year (Hladik, 1988). The
ambiguous term omnivore is used either to describe such flexibility or to
emphasize a supplement of meat included from time to time in a mainly
frugivorous diet. However, it is noticeable that the largest primate species,
especially anthropoids, consume mainly vegetable matter to provide their
protein requirements. Chimpanzees, that occasionally eat the meat of small
mammals, do not receive all their protein requirements from this source,
which is anyway rarely available to females and never exploited by the
youngest animals (Hladik, 1981).

Considering the unspecialised frugivorous-type human gut anatomy, the
dietary history of the genus Homo is likely to display a wide range of
variation. During various historical periods, depending on availability and
the nutrient content of food resources, our human ancestors would mostly
have consumed either vegetable or animal matter (Isaac et al., 1981; Gordon,
1987; Couplan, 1997). The present consensual picture of our past feeding
behaviour includes three major phases: (1) After the late Miocene climate
shift, hominid feeding behaviour in changing environments progressively
shifted from a mainly vegetarian diet to a diet including more and more
animal matter, either from hunting and/or from scavenging; (2) the hunter-
gatherer way of life and the resulting diet characterized the mid-Pleistocene
period, but in the late Pleistocene, during the ice-ages, hominids had to
specialize in large game; (3) these successive phases, as described by
Gordon (1987), were followed by progressive control of animal and
vegetable resources through domestication and cultivation, allowing some
human groups to eat more vegetable matter than during previous periods.

['(2) archaeological evidence from the Plio-Pleistocene, coincident with
the emergence of Homo can be read to reflect low-yield scavenging, *not*
hunting. Our review of the archaeology yields results consistent with these
critiques: [..] (2) meat was consumed at or near the point of acquisition,
not at home bases, as the hunting hypothesis requires; (3) carcasses were
taken at highly variable rates and in varying degrees of completeness, making
meat from big game an even less reliable food source than it is among
modern foragers. Collectively, Plio-Pleistocene site location and assemblage
composition are consistent with the hypothesis that large carcasses were
taken *not* for purposes of provisioning, but in the context of competitive
male displays. Even if meat were acquired more reliably than the archaeology
indicates, its consumption cannot account for the significant changes in life
history now seen to distinguish early humans from ancestral australopiths.
...'
http://www.ingentaconnect.com/conten...00006/art00604 ]

Meat was consumed, but it is unlikely that animal flesh (especially lean meat)
was a staple for long periods. As highlighted by Speth (1989, 1991), fat and
fatty meat provide energy for meat eaters, and lean meat can rapidly
become unhealthy if used as an only food. During "lean periods", meat
must be complemented with vegetable matter as an energy source, especially
to provide the necessary energy for reproduction.

The high quality foods needed to provide enough energy for the incipient
hominids could have been drawn from alternative sources rather than the fat
meat of large game. Wrangham et al. (1999) have provided a new and very
exciting hypothesis on the possible process of hominization, made possible
by the early use of fire for cooking. As far back as 1.9 My (Plio-Pleistocene),
the first Homo Erectus tended towards a large body (and brain size), for
both sexes, with a reduction of teeth. This was possible by (and likely to
be selected for) a shift to a high caloric diet that did not require much
mastication. Either a cooked fatty meat or a cooked wild tuber may have
provided this type of diet. Cooking in embers considerably improves the
taste and texture of both kinds of food and may explain why it could have
been rapidly adopted by hominids able to master the technique of fire (with
brain increase obviously related to technical skills). However, the best
efficiency for obtaining calories would be with cooked starchy tubers (50%
more energy from starch after cooking). Furthermore, most wild yam species
are non-toxic and available in large quantities throughout African forests and
savannas (A. Hladik and Dounias, 1993). Although clearly identified long-
lasting hearth locations have never been found by archaeologists before the
mid-Pleistocene, the evidence of early utilisation of fire based on charcoal
residue fragments mentioned by Wrangham et al. would be quite a convincing
argument for anyone who has recently visited an abandoned Pygmy forest
settlement, and searched for tiny pieces of charcoal. After a few months, no
obvious trace of a hearth is visible, although meat and tubers,wrapped in
large leaves, have been cooked in the embers by the Pygmies.

Consequently, meat eating certainly played an essential part in hominid history,
but the hominid flexible gut anatomy permitted adaptation to various diets.
Taking into account the allometric factors in the comparative study of primate
gut anatomy, there is no evidence to support theories such as a change in gut
anatomy that allowed carnivorousness and a simultaneous increase in brain
size. Alternatively, the early cooking of gathered foods - and the nutritional,
behavioural and social consequences of this pattern - could have been a major
milestone in the hominization process.

http://www.publicaciones.cucsh.udg.m...om19/21-31.pdf

'At Klasies River, traces of burned vegetation suggest that the ancient
hunter-gatherers may have figured out that by clearing land, they could
encourage quicker growth of edible roots and tubers. .
...'
http://www.smithsonianmag.com/histor...tml?c=y&page=3

> Speaking of enzymes, we know that even within a few thousand previous
> years
> adaptations to local foods and changes in diet have caused the genetic
> source for them to be toggled on and off and to be replaced. How do we
> know
> what they observe about one related to digestion of starch is not in fact
> a
> reflection in the past 10 thousand years of a shift to more grain and
> other
> intensely starch rich diets?

'Multiple lines of evidence now indicate that the ability to digest large
quantities of starch may have been a crucial adaptation in human evolution
-- providing the calories needed to grow large, cognitively-sophisticated
brains capable of complex language and social cooperation. This idea is a
serious departure from the leading hypothesis that carnivory (via hunting)
was the dietary shift needed to support large brains in early humans.

The breakthrough study, lead by George Perry of Arizona State University
and Nathaniel Dominy of UC Santa Cruz
(http://www.nature.com/ng/journal/v39...s/ng2123.html), first
demonstrates that individuals with more copies of the AMY1 gene tend to
have higher levels of amylase in their saliva. The researchers then sampled
a suite of high- and low-starch populations spanning cultures world-wide--
Hadza hunter-gathers who survive primarily on roots and tubers, and two
agricultural populations (Japanese and European Americans) comprised the
high-starch sample. Low-starch populations, of which there are considerably
few, included rainforest hunter-gatherers (Biaka and Mbuti) and pastoralists
(Datog and Yakut). In line with expectations, mean AMY1 copy number
was greater in the high-starch compared to low-starch populations.

Notably, there was no geographic pattern in AMY1 copy number to suggest
that populations closer to one another have more similar AMY1 copy numbers
than populations that are further apart-- this pattern would be expected if
variation in AMY1 is driven largely by neutral genetic changes (genetic drift).
Instead, the results suggest that variation in AMY1 is related to ecological
adaptations in diet. Perry and Dominy hypothesize that natural selection is
driving differences in AMY1 copy number. Their results do provide some
compelling evidence for natural selection at the AMY1 locus, but the authors
cautiously note that the jury is still out on this question-- pending additional
data of course.

Shedding some light on the evolutionary history of AMY1, Perry and Dominy
also looked at AMY1 variation in chimps and bonobos, our close genetic
relatives. Their primary diet-- ripe fruit-- contains very little starch, leading the
researchers to predict low numbers of AMY1 in these apes. Indeed, the data
indicate that chimps and bonobos have, at most, 2 functional copies of AMY1.
The researchers report that humans have 3 times more AMY1 copies
compared to chimps, on average-- and bonobos may not have any functional
AMY1 copies at all. These findings support the conclusion that elevated
AMY1 copy numbers arose in the human lineage, not before it.

If this doesn't convince you, Dominy and colleagues have also found evidence
that Homo erectus, an early human progenitor, specialized on eating high-starch
corns and tubers. In this sister study, Dominy used stable isotope analysis, a
common method to assess diet composition. In a nutshell, the stable isotope
signatures of consumers will resemble the stable isotope signatures of their food
sources-- after some corrections for fractionation. As it turns out, Homo erectus
has a stable isotope signature that is consistent with a high-starch diet, and
decidedly not consistent with a carnivorous one.

All of these lines of evidence suggest that having many copies of AMY1 is likely
to have evolved early in the human lineage-- indeed it may have been critical to
launching humans on our own immensely successful, starch-filled, evolutionary
path.

http://thexvials.blogspot.com/

> Speaking also of enzymes, what is the specific function of elastase in the
> human metabolism and how does it relate to changes in human diet?

Again? Remember "It is present in all vertebrates above the jawless fish"?

So how does it relate to changes in the diet of horses, deer, elephants, ...?