site conservation

This seems bad:

Wastewater runoff from a golf-course irrigation system is threatening research at caves along South Africa's southern coast that contain the earliest evidence of humans exploiting marine resources, scientists say. To their disappointment, a judge here declined last week to issue an injunction designed to protect the archaeological site.

Water is leaching down through the rock into the caves, including Pinnacle Point (which I wrote about here). The leaching is obviously not good, because it mucks up the chemistry in the sediments, and the sheer presence of extra water may screw with the dating models.

In last week's Science, Stanislas Dehaene and colleagues describe the relation of cultural invention to "universal intuition" about mathematical logic:

The mapping of numbers onto space is fundamental to measurement and to mathematics. Is this mapping a cultural invention or a universal intuition shared by all humans regardless of culture and education? We probed number-space mappings in the Mundurucu, an Amazonian indigene group with a reduced numerical lexicon and little or no formal education. At all ages, the Mundurucu mapped symbolic and nonsymbolic numbers onto a logarithmic scale, whereas Western adults used linear mapping with small or symbolic numbers and logarithmic mapping when numbers were presented nonsymbolically under conditions that discouraged counting. This indicates that the mapping of numbers onto space is a universal intuition and that this initial intuition of number is logarithmic. The concept of a linear number line appears to be a cultural invention that fails to develop in the absence of formal education (Dehaene et al. 2008:1217).

The idea is that children in Western societies have to learn that a number line is a linear representation; they begin by compressing the space devoted to large numbers:

When asked to point toward the correct location for a spoken number word onto a line segment labeled with 0 at left and 100 at right, even kindergarteners understand the task and behave nonrandomly, systematically placing smaller numbers at left and larger numbers at right. They do not distribute the numbers evenly, however, and instead devote more space to small numbers, imposing a compressed logarithmic mapping. For instance, they might place number 10 near the middle of the 0-to-100 segment. This compressive response fits nicely with animal and infant studies that demonstrate that numerical perception obeys Weber's law, a ubiquitous psychophysical law whereby increasingly larger quantities are represented with proportionally greater imprecision, compatible with a logarithmic internal representation with fixed noise (7, 20, 21). A shift from logarithmic to linear mapping occurs later in development, between first and fourth grade, depending on experience and the range of numbers tested (17-19).

They note that there's a problem testing these ideas in Western children, who are surrounded throughout their development by numbers -- in books, "elevators" and other places. Most of these numbers are small ones -- especially one through ten -- so they might naturally accentuate the ones they know.

They found when testing the Mundurucu that both adults and children tended to compress the high end of the number scale, even testing numbers between one and ten. This compression is logarithmic -- they accentuate contrasts between small numbers disproportionately. It makes sense logically -- we care more about detailed contrasts between small numbers than large numbers. They don't give an idea of which logarithm people are using; and in fact it may be different ones for different people. The important fact is the small number/large number contrast.

Dehaene and colleagues attribute this scaling to mapping at the neural level:

What are the sources of this universal logarithmic mapping? Research on the brain mechanisms of numerosity perception have revealed a compressed numerosity code, whereby individual neurons in the parietal and prefrontal cortex exhibit a Gaussian tuning curve on a logarithmic axis of number (27). As first noted by Gustav Fechner, such a constant imprecision on a logarithmic scale can explain Weber's law -- the fact that larger numbers require a proportional larger difference in order to remain equally discriminable. Indeed, a recent model suggests that the tuning properties of number neurons can account for many details of elementary mental arithmetic in humans and animals (21). In the final analysis, the logarithmic code may have been selected during evolution for its compactness: Like an engineer's slide rule, a log scale provides a compact neural representation of several orders of magnitude with fixed relative precision.

From that perspective, the Western conception of the number line appears as a very distinctive invention, capable of adjusting the logarithmic encoding to arrive at faster and more accurate mathematical conclusions about large numbers. The authors speculate that addition and subtraction (which display invariance between large and small numbers) and experience with measurement underlay the development of the linear concept in Western children.

References:

Dehaene S, Izard V, Spelke E, Pica P. 2008. Log or linear? Distinct intuitions of the number scale in Western and Amazonian indigene cultures. Science 320:1217-1220. doi:10.1126/science.1156540

Rex Dalton reports on Charles Musiba's efforts to preserve the Laetoli footprints with a new museum:

[The weathering to the trackways] prompted Tanzanian anthropologist, Charles Musiba, now at the University of Colorado in Denver, to call for the creation of a new museum to reveal and display the historic prints. But other anthropologists question this idea -- as they did when the tracks were covered -- because Laetoli is several hours' drive into Ngorongoro National Park, making guarding and maintaining any facility extremely difficult. Musiba presented his proposal for the museum last month at the International Symposium on the Conservation and Application of Hominid Footprints, in South Korea. He says that Tanzania now has the scientific capacity and the funds to construct and monitor a museum.

Dalton quotes Tim White and Terry Harrison as skeptics, citing them as

among a group that favours cutting the entire track out of the hillside, then installing it in a museum in a Tanzanian city

The article weighs pros and cons. Dalton also gives a good description of the problems that arose with previous attempts to preserve the trackways. Initially covered with dirt, the trackways were endangered when acacia trees sprouted and started breaking up the ash layer. The current setup, constructed in 1995, involves a mat overlain by fill, but this is eroding out.

I tend to think they should be managed in a way that maximizes their benefit to local people. It's hard for me to believe that chunking the whole thing out and moving it in trucks halfway across Tanzania would be better than whatever might happen in a poorly-guarded museum. But clearly there are no perfect choices. It is a real challenge to start and build continuing interest in a museum like this without very strong support -- but I would like to see it succeed.

References:

Dalton R. 2008. Fears for oldest human footprints. Nature doi:10.1038/451118a

Julien Riel-Salvatore has been following the fungus problems at Lascaux. His earlier post discusses a December NY Times article on the problem. That article is a really good one, it explains why this fungus problem is different from the white fusarium fungus that preservationists battled in the cave in 2001.

Whatever the reason for the problems at Lascaux, the white mold outbreak in 2001 led the government to close it to all nonessential visitors.

It was so serious that, to stop the invasion, the floor was covered with quicklime and scientists began treating the problem chemically, said Marc Gauthier, president of the International Scientific Committee for Lascaux, which was created as a result of the crisis.

The new problem at Lascaux, however, does not appear to be linked to the fusarium fungus. Described by experts as black stains, the blemishes are in fact both gray and black. "They vary from a few millimeters to 4 centimeters," said Mr. Geneste, noting that most are found in the passages where the rocks are most porous and paintings had faded the most long before modern man entered. While only a few stains have affected the paintings, they have now been found in some 70 different spots.

Now, Julien links to a more recent story from the CBC, which describes the political pettifog between the International Scientific Committee and the French government:

[The team of specialists] put pressure on the French government by alerting UNESCO, which classifies the caverns as a World Heritage Site, about the conditions.

Laurence Leaute-Beasley, president of the International Committee for the Preservation of Lascaux, called for the management of the caves to be taken out of the hands of the French government, saying someone who understands the science involved should take over.

The French government, not wanting such an an important site to be seen as neglected, has decided to accept the committee's advice and act now against the fungus.

So they were threatening to bring the UN into France to fight an invasive subterranean fungus. Don't tell the "black helicopter" believers!

The experts disagreed on the cause of the problem. Some say global warming is to blame, others that human activity in the caves is exacerbating the problems.

Global warming is not to blame. It's not a totally silly idea -- the Times article discusses an increase in the average soil temperature around several caves, and Lascaux is a relatively shallow one that might be influenced by increasing soil temperatures. But the climate around these caves has fluctuated a whole lot more during the last 20,000 years than in the last 20. The important recent changes have been caused by people -- walking into the cave, lighting the cave, ventilating the cave.

But now that the changes have been initiated, they can't be solved by people just leaving the cave alone. It seems like such a curious contrast -- archaeologists know they must destroy the sites to learn from them; art historians must preserve their objects to learn from them. Lascaux is both site and object, and has faced both pressures.