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Note: The following news item is drawn in part from a story in the 15 May 2004 issue of Science News titled "Expanding the Code," by B. Bower.
The so-called "code of life" is the mapping from groups of three DNA bases to amino acids. When a cell reads the directions in DNA to make proteins, it reads DNA in groups of three bases called codons. In addition to 61 codons that code for amino acids, the building blocks of protein, there are three codons that tell the cell to stop synthesizing protein from a given nucleic acid strand. In the past, scientists have engineered cells to use an additional amino acid by re-engineering the protein synthesis biochemistry to use one of the "stop" codons to code for incorporation of the new amino acid into a protein. With at least one "stop" absolutely required, this leaves room for only two novel amino acids even if the technique is pushed to its limit.
A team led by Peter Schultz at the Scripps institute in La Jolla, California, has modified the code of life in a new way to permit the use of more amino acids. The Schultz lab has modified a strain of e-coli to use the four-base DNA pattern AGGA to code for a new amino acid, a more difficult feat than re-engineering an existing "stop" codon. If four-base codons are used, the number of available patterns is quadrupled from 64 to 256. Keeping the rest of the cell's biochemistry on track probably means that full use of these 192 additional patterns is not practical, but this advance does open the door to the incorporation of dozens of new amino acids. A tour-de-force of biochemistry, the full impact of this technique will not be known until vastly more experimentation has been performed.
Note: The following news item is drawn in part from a story in the 16 April 2004 issue of Science titled "Oldest Beads Suggest Early Symbolic Behavior," by Constance Holden.
About 40,000 years ago, the human species found art. Dubbed the creative explosion, this period of time has yielded evidence from cave paintings to jewelry that demonstrates our species had firmly grasped the concept of symbols and was engaging in symbolic thinking. Current thought holds that there was an evolutionary leap forward in human mental processes during this period.
In a recent issue of Science, findings of much older artistic endeavors are reported. Beads carved from snail shells and ostrich egg shells that are between 75,000 and 110,000 years old suggest our species was manufacturing jewelry at least 35,000 years earlier than the creative explosion. Exact dating of associated bone fragments will soon yield more accurate figures for the date of these beads. In any case, the known age of creativity and symbolism as aspects of the human mind has now been roughly doubled.
Note: The following news item is drawn in part from a story in the 15 May 2004 issue of The Economist titled "Quoth the Raven," by staff writers.
How do you tell if a creature is aware of itself? One approach is to try to determine if it has a theory of mind. A creature has a theory of mind if it acts as if it thinks other creatures have minds. Gorillas and goats have been shown to have theories of mind, and now it appears that Ravens also have theories of mind.
As reported in a recent issue of the Economist, Bernd Heinrich and Thomas Bungnyar of the University of Vermont in Burlington have found evidence of a theory of mind in Ravens. A creature with a theory of mind, by trying to imagine what other creatures are thinking, can gain information from them. In this case the Ravens were placed on the far side of a partial barrier from a human experimenter. The experimenter would then gaze fixedly at some point in the room either within the Ravens field of view or concealed behind the barrier. Six young and one older raven were used in the experiment. All seven ravens followed the experimenter's gaze. When the researcher gazed at a point hidden from the ravens, they would move to a point in the room where they could see the point the experimenter was looking at.
The best results from the study did not come from the gaze experiments, but rather occurred during a study to see what Ravens could learn from one another during foraging. A pair of ravens was given access to a collection of closed containers, some of which held food and some of which did not not. One of the birds in the pair was skilled at finding containers with food. The other bird in the pair, while unskilled at finding containers with food, was relatively larger in size. At the start of the experiment, the larger bird would bully the smaller one into giving up the food it found. During the course of the experiment, the smaller bird began to demonstrate behavior consistent with having a theory of mind. After opening a container with food, and being chased away from this container by the larger bird, the smaller bird would then open empty containers and exclaim over them as if they contained food. The larger bird would then come over to take away the new food, and the smaller bird would rush back to eat the food from the original container.
Deception requires a theory of mind. Successfully deceiving another raven requires a raven to think that such deception is possible. Perhaps "bird brained" is not the insult we imagine it to be.
Note: The following news item is drawn in part from a story in the 24 April 2004 issue of Science News titled "Puzzle on the Edge," by R. Cowen.
Among the bodies in the outer solar system, slow rotation is strongly correlated with having a large moon. The rate a body spins depends on the net angular momentum it had when it formed, plus the effect of any subsequent impacts. On average, bodies with slower rotation rates are slower because their angular momentum equations involve a moon. Jupiter, which spins at the relatively fast rate of about once every ten hours, has only comparatively small moons. Pluto, a relatively slow spinner, has a relatively large moon (Charon) which is 20% of it's size.
Recently, however, another body has been found in the outer solar system at a record-breaking distance from the sun. This body, named Sedna, is about two-thirds the size of Pluto and spins at a very slow rotation rate: once every twenty days. Careful observation with the Hubble space telescope, however, has found no moon. It might be that Sedna is simply deep in the tail of the distribution of angular momentum among outer system bodies, perhaps because of an unusual impact.
Note: The following news item is drawn in part from a story in the 24 April 2004 issue of The Economist titled "Plumbing the Depths," by staff writers.
A barrier to assessing human impact on the environment is the pesky lack, through much of history, of measurements of ecological variables such as temperature, rainfall, atmospheric composition, and sea level. These measurements can sometimes be deduced from nature. The Greenland ice pack, for example, can be sampled for trapped air bubbles thousands of years old.
About 15 B.C., King Herod of Judea caused the city of Caesarea to be built about 15 miles south of Haifa, near the seashore. The wells in this city have a narrow depth range that permits fresh water to accumulate in the well without permitting the entry of salt water. The depth of the wells is thus a good surrogate for the level of the eastern Mediterranean sea during this period. Caesarea was inhabited continuously for 1,300 years, with wells dug and abandoned from time to time. Abandoned wells were filled with household garbage, including datable pottery shards. Analysis of this evidence indicates that the sea level near Caesarea did not change much during the period the city was inhabited, and that this sea level was from six to ten feet lower than the current sea level. This suggests that, in historical terms, the current rate of sea level rise of 1mm per year is quite rapid.
Note: The following news item is drawn in part from a story in the 8 May 2004 issue of Science News titled "Toxin Takeout," by S. Milius.
The brilliant coloring of poison arrow frogs and their tree-frog relatives in Central and South America is a warning. In plain language, it informs predators that the frogs are poisonous and directs them to look elsewhere for a meal. Researchers studying these frogs have found that, when raised in captivity, they do not develop the toxins that protect them in nature. This suggests that the frogs cannot synthesize their own poisons and are instead obtaining them from some environmental source.
A team led by John Daly of the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland, has found a source for many of these frog poisons. Formicine ants, a family that includes the familiar carpenter ant, contain many of the compounds that give poison arrow frogs their edge. These ants are found on the same water-catching plants where tree-frogs lay their eggs. The discovery of these compounds in the ants triples the number of frog toxins with a known dietary source. Interestingly, many of the compounds are not ones that the ants themselves can synthesize. The search for the ultimate source of these toxins awaits further analysis of the eating habits of the ants.
Note: The following news item is drawn in part from a story in the 8 May 2004 issue of The Economist titled "It Figures," by staff writers.
In biological terms, it is to the advantage of potentially good mates to advertise their quality. Creatures thus often evolve visible signs of hidden strengths. For example, symmetry is an attractive quality for a wide range of species and is used to demonstrate a low parasite load. It now seems that female humans also engage in this form of biological signaling.
A study was performed that divided women into four categories based on hip-to-waist ratio and breast size: low-small, low-large, high-small, and high-large. Two hormones that determine fertility were measured throughout the menstrual cycle. Women with a high hip-to-waist ratio had elevated levels of one of the hormones. The women with both a high hip-to-waist ratio and large breasts had elevated levels of both hormones. Their fertility was approximately three times that of average women. From a purely biological perspective, this is a substantial advantage.
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