'Safe' Ultraviolet Rays May Cause Cancer

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'Safe' Ultraviolet Rays May Cause Cancer

http://wrightworld.net/science.htm

 

3-27-04 NEW YORK Ultraviolet-B (UVB) rays are the component of sunlight

that cause sunburn, while ultraviolet-A (UVA) rays, which produce a tan, are

thought to be relatively safe. Now, however, Australian and US researchers

report that UVA induces a greater number of mutations in the deep layer of

skin, where skin cancers arise, than does UVB light. Far more UVA light than

UVB light penetrates to the basal layers of skin, the scientists point out

in an article in the Proceedings of the National Academy of Sciences.

However, UVA appears to cause less direct damage to DNA than UVB and has

been " considered far less carcinogenic. " Dr. Nita S. Agar from University of

Sydney and colleagues used the distinctive " fingerprints " of UVA and UVB

damage to DNA to examine which types of rays were causing mutations in deep

and shallow skin layers in skin cancers and in pre-malignant solar

keratoses. All UVB mutations in solar keratoses and 82 percent of UVB

mutations in squamous cell carcinomas were located in the upper skin layers,

the authors report, whereas most UVA mutations (57 percent and 86 percent,

respectively) were found in the basal layers. Further analysis also showed

unrepaired DNA damage induced by recent UVB exposure in the upper layers. In

the basal layers, unrepaired damage induced by UVA exposure was predominant.

" The identification of UVA mutations in both (skin cancers) and premalignant

solar keratoses in almost identical proportions implicates an early role for

this band of radiation in tumor progression, " the investigators comment.

" Given the traditional emphasis on UVB, " they conclude that protection " also

from UVA irradiation has profound implications on public health worldwide. "

SOURCE: Proceedings of the National Academy of Sciences, online early

edition, March 22, 2004.

 

Weaker Jaws Were Traded for Big Brains -

 

Study 3-25-04 LONDON - A genetic mutation that occurred 2.4 million years

ago could be the reason why modern humans have such big brains and weak

jaws, scientists said on Wednesday. They discovered that a fault in a gene

called MYH16 in modern humans happened at about the same time that their

skulls started to change in shape from other primates, allowing their brains

to increase in size. But the trade-off was a smaller, less powerful jaw.

" The coincidence in time...may mean that the decrease in jaw muscle size and

force eliminated stress on the skull which released an evolutionary

constraint on brain growth, " said Nancy Minugh-Purvis, a member of the team

at the University of Pennsylvania School of Medicine, that made the

discovery. All humans have the MYH16 mutation but other primates, including

chimpanzees and macaques, still have the intact gene. Over the past few

million years, since the genetic fault occurred, human skulls have grown

three times in size and the outwardly elongated jaws have receded. Pete

Currie, of the Victor Chang Cardiac Research Institute in Sydney, believes

the research published in the science journal Nature could be the first

functional genetic difference between humans and apes. " Remarkably, the

timing of the appearance of this genetic alteration, or mutation, roughly

coincides with the appearance of " human-like " characteristics in the hominid

fossil record, " Currie said in a commentary in the journal.

 

Minugh-Purvis along with Hansell Stedman and other experts at the university

pieced together the complicated puzzle after discovering that the gene was

intact in primates but mutated in all humans. A genetic fault is often

linked with some type of inherited disease but the scientists were puzzled

about what type of disease was common in all humans throughout the world.

Further research revealed that MYH16 was associated with muscles involved in

chewing and biting and it encoded a protein in primate jaw muscles. This led

the researchers to suspect the so-called disease in humans was a weaker

bite. Stedman and his colleague said the weaker bite would have lessened the

force on the skull so it could grow larger and provide more space for a

bigger brain. " We can only hope that this study represents the vanguard of a

new wave of analyzes that focus on the genetic basis of human evolution, "

Currie added. A genetic mutation that occurred 2.4 million years ago could

be the reason why modern humans have such big brains and weak jaws,

scientists said Wednesday. They discovered that a fault in a gene called

MYH16 in modern humans happened at about the same time that their skulls

started to change in shape from other primates, allowing their brains to

increase in size. But the trade-off was a smaller, less powerful jaw.