Wednesday, January 23, 2008

Monday, January 21, 2008

Bones From French Cave Show Neanderthals, Cro-Magnon Hunted Same Prey

Finding: A 50,000-year record of mammals consumed by early humans in southwestern France indicates there was no major difference in the prey hunted by Neanderthal and Cro-Magnon.

Research findings counter the idea proposed by some scientists that Cro-Magnon, who were physically similar to modern man, supplanted Neanderthals because they were more skilled hunters as a result of some evolutionary physical or mental advantage.

The new study suggests Cro-Magnon were not superior in getting food from the landscape. Archeoligists could detect no difference in diet, the animals they were hunting and the way they were hunting across this period of time, aside from those caused by climate change.

The takeover by Cro-Magnon does not seem to be related to hunting capability. There is no significant difference in large mammal use from Neanderthals to Cro-Magnon in this part of the world. The idea that Neanderthals were big, dumb brutes is hard for some people to drop. Cro-Magnon created the first cave art, but late Neanderthals made body ornaments, so the depth of cognitive difference between the two just is not clear.

Bears, Caves, and Cro-magnon
The study also resurrects a nearly 50-year-old theory first proposed by Finnish paleontologist Björn Kurtén that modern humans played a role in the extinction of giant cave bears in Europe. Cro-Magnon may have been the original "apartment hunters" and displaced the bears by competing with them for the same caves the animals used for winter den sites.

The cave has a rich, dated archaeological sequence that extends from about 65,000 to about 12,000 years ago, spanning the time when Neanderthals flourished and died off and when Cro-Magnon moved into the region. Neanderthals disappeared from southwestern France around 35,000 years ago, although they survived longer in southern Spain and central Europe.
The researchers were most interested in the transition from the Middle to Upper Paleolithic, or Middle to Late Stone Age.

Neanderthals occupied Grotte XVI as far back as 65,000 years ago, perhaps longer. Between 40,000 and 35,000 years ago, people began making stone tools in France, including at Grotte XVI, that were more like those later fashioned by Cro-Magnon. However, human remains found with these tools at several sites, were Neanderthal, not Cro-Magnon. Similar tools but no human remains from this time period were found in Grotte XVI and people assumed to be Cro-Magnon did not occupy the cave until about 30,000 years ago.

The researchers examined more than 7,200 bones and teeth from large hoofed mammals that had been recovered from the cave. The animals – ungulates such as reindeer, red deer, roe deer, horses and chamois were the most common prey – were the mainstay of humans in this part of the world, according to Grayson.

He and Delpech found a remarkable dietary similarity over time. Throughout the 50,000-year record, each bone and tooth assemblage, regardless of the time period or the size of the sample involved, contained eight or nine species of ungulates, indicating that Neanderthals and Cro-Magnon both hunted a wide variety of game.

The only difference the researchers found was in the relative abundance of species, particularly reindeer, uncovered at the various levels in Grotte XVI. At the oldest dated level in the cave, reindeer remains accounted for 26 percent of the total. Red deer were the most common prey at this time, accounting for nearly 34 percent of the bones and teeth. However, as summer temperatures began to drop in Southwestern France, the reindeer numbers increased and became the prey of choice. By around 30,000 years ago, when Cro-Magnon moved into the region, reindeer accounted for 52 percent of the bones and teeth. And by around 12,500 years ago, during the last ice age, reindeer remains accounted for 94 percent of bones and teeth found in Grotte XVI.

Grayson and Delpech also looked at the cut marks left on bones to analyze how humans were butchering their food. They found little difference except, surprisingly, at the uppermost level, which corresponds to the last ice age.

It is possible that because it was so cold, people were hard up for food. The bones were very heavily butchered, which might be a sign of food stress. However, if this had occurred earlier during Neanderthal times, people would have said this is a sure sign that Neanderthals did not have the fine hand-eye coordination to do fine butchering.
In examining the Grotte XVI record, the researchers also found a sharp drop in the number of cave bears from Neanderthal to Cro-Magnon times.

Cave bears and humans may have been competing for the same living space and this may have led to their extinction. He added that it is not clear if the decline and eventual extinction of the bears was driven by an increase in the number of humans or increased human residence times in caves, or both.

If we can understand the extinction of any animal from the past, such as the cave bear, it gives us a piece of evidence showing the importance of habitat to animals. The cave bear is one of the icons of the late Pleistocene Epoch, similar to the saber tooth cats and mammoths in North America. If further study supports the argument, we finally may be in a position to confirm a human role in the extinction of a large Pleistocene mammal on a Northern Hemisphere continent.

Monday, January 14, 2008

Biogeographic distributions

I. Three important principles:
How do these principles support descent with modification?
A. Environment cannot account for either similarity or dissimilarity, since similar environments can harbor entirely different species groups
B. "Affinity" (=similarity) of groups on the same continent (or sea) is closer than between continents (or seas)
C. Geographical barriers usually divide these different groups, and there is a correlation between degree of difference and rate of migration or ability to disperse across the barriers.

Disjoint locations for the same extant species: Is this evidence for creation? Note that Evolution proposes Single Centers for the origins of species, so Discontinuous Distributions need to be explained.
A. this means that a method of dispersal must be proposed.
1. Changes in climate or geology must have affected migration (i.e., by first allowing migration and then preventing migration)
2. Darwin designed tests of a priori assumptions
3. Although "accidental", dispersal is not really random (and thus allows very specific predictions about distributions in some cases)

B. Case study: Similarity of flora and fauna at mountain summits (is this evidence for independent creations or something else?)
1. Evidence is clear for recent glaciation
2. Migrations are easily visualized in the gradual advances and retreats of glaciers
3. Because mountain tops retain a colder climate, some cold-adapted, northern species would be retained on mountain tops (and thus isolated during glacial retreat)
4. Also explains why such mountain-top species are most closely related to species living due north
5. Isolation poses an opportunity for change, esp. if it means a change in its interspecific associations
6. Assumption of the scenario: Circumpolar distribution is uniform (presently the case)
7. Secondary assumption: Similar situation for subarctic species

C. Many difficulties remain to be solved, esp. the very distinct, but distantly related forms in the Southern hemisphere (e.g., marsupial versus placental mammals)
1. These species are too distinct to be explained by the recent glaciation
2. Darwin postulates an earlier glaciation, because he did not know about plate tectonics
3. With plate tectonics, many (if not all) of these kinds of problems are soluble.

Fresh water distributions
Because freshwater is isolated, you might expect restricted ranges, however, this is not the case just the opposite, they often have distributions even broader than terrestrials: How can this be explained? Three cases to consider:
A. Distribution of Fish
B. Distribution of Shells (molluscs)
C. Distribution of Plants (often very wide ranges)
In all cases, dispersal of freshwater organisms depends largely on animal (esp. bird) transport
Distribution of species on oceanic islands
Darwin considered this evidence as especially strong in its support of descent with modification
A. The total number of species on oceanic islands is small compared to the number on an equal area of continent
B. Proportion of endemic species is very high
C. Oceanic islands are missing entire Classes
D. Endemic species often possess characters that are adaptive elsewhere, but are useless characters on the island
E. Endemic species often show (new) adaptive traits not possessed by any of their relatives
F. Batrachians are universally absent (except one frog in New Zealand)
G. Terrestrial mammals are not found on any island >300 miles from mainland
H. But arial mammals are found on such islands, and many of these are endemic
I. Also a correlation between the depth of the sea separating islands inhabited by mammals and the degree of "affinity" (classification) between these species
J. "The most striking and important fact" (p. 397) is the affinity of these island species to those of the nearest mainland, without being actually the same species
K. Within an archipelago, species are more closely related to each other than to those on the mainland (but still distinct from each other)
L. The principle applies widely that island inhabitants are most closely related to the inhabitants of a region from which colonization is possible
M. According to this principle, it must be the case that at some former time, a single parental species covered both ranges (i.e., the migration event itself)N. Darwin draws a parallel between Time and Space in the "Laws of Life"

Monday, January 7, 2008

Greenland: Oldest DNA Shows Warmer Planet

Greenland: Scientists studying the glaciers probed two kilometers and recovered the oldest plant DNA. Their studies also showed that the earth was much warmer hundreds of thousands of years ago than is generally believed.

Using the DNA of trees, plants and a variety of insects from underneath the southern Greenland glacier estimated to date from 500,000 to 900,000 years ago.

So what is the prevailing view that a forest of this kind could only have existed in Greenland as recently as 2.4 million years ago. This means that if the area supported these plants and insects, it was warmer than previously thought.

The DNA samples showed that the temperature may have reached 50 degrees Fahrenheit in the summer and 1 degree F in the winter.

Another finding showed that during the last period between ice ages, between 116,000-130,000 years ago, temperatures were on average 9 degrees F higher than now, so the glaciers on Greenland did not completely melt away.