Saturday, August 30, 2008

The Mysteries Of Camouflage And Mimicry

In nature, any species is sought after by other predator or prey species, which detect it through their senses (sight, hearing, smell). Victims can defend through venoms, unpleasant smells, run, or by deceiving the sensory input of their predators. One method is camouflage and mimicry. It is a balance between prey and predator bypassing this defense.

To camouflage (homochromy) in order to escape predators or to surprise the possible preys is to melt into the hues and shapes of the environment. The method can be simple or elaborated (the inversed shadow), making the animal melt into its environment.

Polar animals, like the polar bear and polar owl, are white. In the savanna, lions employ camouflage. They remain for large periods of time immobile in the bush without anybody being aware they are there, due to their tawny color. This tactic is especially efficient during the dry season, when the prey is scarce and the lions cannot afford losing food for being detected early by their prey. The same camouflage color is used by the African ground squirrels or prairie dogs, which use the autumn hues in their coat for deceiving predators.

Many insects (like grasshopers), snakes and birds (like parrots) have a green color that makes them difficult to distinguish in the grass or in the forest. Movie makers spend a lot of time detecting a leopard in the wild, even if they are abundant in an area... Most bottom fishes, like rays and angelfish, cannot be distinguished from the substrate. Some animals have cryptic shadow: they are dark above and light below, like tuna and many other fishes.

Homochromy can change with the season, like the ptarmigan and arctic hare, which are brown in the summer and white during winter.

Homotypy goes further than camouflage: the animals copy natural elements or plant organs with an amazing precision. Stick insects really look like a stick (their name Phasmatodea comes from the Greek "phasma" "phantom") and even imitate during their movements the shaking of a stick blown by the wind. Some Thai stick insects even mimic dead branches covered by lichens. The same imitation is made by some caterpillars and beetles (like Petrognatha gigas of western Africa). Leaf insects not only imitate a green leaf with nerves, but also the attack of fungi on the imaginary leaf! The same patterns are achieved by some Brazilian locusts.

The leafy sea dragons, relatives of the sea horses, can be differentiated with difficulty from algae.

Orchid mantis (Hymenopus coronatus) from southeastern Asia mimics so well a pink flower, that pollinating insects go straight into the killing arms of this predator, while others praying mantis from the same are mimic tree bark. Many moths too mimic tree bark.

Some caterpillars replace a plant bud before turning into a cocoon and the cocoon looks exactly like the replaced bud.
The tiny black toads (Oreophrynella) from the Roraima tepui in Venezuela have the color and texture of the rocks on which they live and this is also the case with many butterflies and the tree bark or dead leaves.

Some butterflies from Costa Rica completely lack color, being completely transparent. The frogmouths from Australia and nightjars have a plumage that makes them difficult to distinguish from the tree bark.

The chameleons' ability to change color is well-known, depending in which environment they are found at a given moment. But they are amateurs compared to the ability of the octopuses, cuttlefish or flounders.

Some animals play dead as an active method of defense: many predators will only eat prey which is alive...The opossum is the most famous when it comes to playing dead, hence the term "playing possum". Many snakes, too, use this strategy, and besides the immobility, they expel through some anal glands a decomposing corpse scent... Besides discouraging animals that eat only living prey, playing possum also convinces some large animals that the individual is no threat to their young.
Many insects (like wasps or caterpillars), spiders, venomous fish and snakes (like kraits and coral snakes) and toxic amphibians (like salamanders, fire-bellied toads and poison dart frogs) warn about their toxicity through bright colors and elaborated patterns.

That's why many species have developed mimicry: imitating the colors and patterns of the real dangerous animals, so that their predators won't attack them, being deceived.

There are flies imitating the color of the wasps and many non-toxic butterflies imitating toxic species of butterflies. Over 15 genera of non-venomous snakes imitate in Americas the model of the highly venomous coral snakes... The Myrmecium spiders mimic nasty ants.

There are even non-toxic moths imitating the ultrasounds emitted by toxic moths, being avoided this way by the bats. Sometimes, the predator imitates the prey, to get closer easier, like in the case of some beetles. Some parasite flies imitate the bumble bees in whose nest they depose their eggs.
The caterpillar of a hawk moth, Hemeroplanes ornapus, from Central America, has a length of 8-10 cm (3.2-4 in). When menaced, the pseudopods of the rear part hold the body (using sucking cups), while the thorax dilates to maximum, and this coupled with two fake shiny eyes and the hanging of the fore part of the body, make the caterpillar resemble a small snake.

Saturday, July 19, 2008

Cleopatra's Mystery Lives On

Reports of Cleopatra's beauty are apparently exaggerated, according to articles published in the British media. On the occasion of her exhibition this month in the British Museum in London, some reports in the media would have us believe that Cleopatra was hook-nosed, dumpy and had bad teeth!
A report in a "quality" publication said that "Cleopatra, the queen of ancient Egypt who seduced Julius Caesar and Mark Anthony with her supposedly irresistible beauty, has been revealed as short, frumpish and in need of a good dentist.. eleven statues show the queen as plain looking with a streak of sterness, and (she) appears to be plump".
Yet, throughout the lengthy reports, no hard evidence was given for the ugly cartoons published supposedly depicting the legendary queen. Furthermore, no explanation has been given for her magical influence and ability to seduce the most powerful men of her time. Her charm was attributed only to strength of character and mental charisma.
Even the statues on display and the coins carrying Cleopatra's head show a royal looking image with firm features and wide eyes. There may be a slight exaggeration of the nose proportion in one of the statues, but the coin illustrates a fine pointed nose, in good proportion to the face. Cleopatra was certainly not ugly.
Unless it is a publicity stunt for the exhibition, no self-respecting Egyptologist would take such descriptions of Cleopatra seriously. Even the curators of the British Museum admit that very few portraits of the queen survived, and they are anything but consistent. The evidence of contemporary description of Cleopatra was discounted out of hand, in these reports, because the writers, such as Cicero, were born a few years after Cleopatra's death. There was mention of her irresistible charm, her seductive voice and eloquent speech. Cicero wrote in the first century BC:
"Her character, which pervaded her actions in an inexplicable way when meeting people, was utterly spellbinding. The sound of her voice was sweet when she talked".
The evidence given for being fat, is also flimsy. Her ancestors were believed to suffer from weight problems! There is also no evidence of Cleopatra being only 5 ft. tall, except a description in a recent catalogue that she was "petite". As for the alleged teeth problem, that was attributed to "…eating the awful Egyptian bread"! In the same report, the ancient queen was described as "…taking care of herself. Her diet, including plenty of fruit and vegetables as well as fish and meat, was healthily balanced". This apparent contradiction was not explained by the writer.
The issue of Cleopatra's beauty is beyond doubt. The love of two powerful men of her era testified to that. Caesar went as far as putting up a golden statue of Cleopatra in the Temple of Venus in Rome, making her the first living human to share a temple with a Roman God - a frank recognition of her divinity and beauty by Caesar himself.

Friday, July 18, 2008

Humans Became Humans Just 4 Million Years Ago

In a common evolutionary trunk, it is known that the orangutan is our cousin thrice removed, the gorilla is our cousin twice removed and the chimp is our first cousin (with which we share 96 % of our genetic information). A new research led by an international team from North Carolina State University, University of Aarhus in Denmark and the University of Oxford in Britain found that chimpanzees and humans split off
from a common ancestor just 4 million years ago, much later than the current hypotheses, that state for 5 to 7 million years ago.The research team compared DNA patches of humans and all big apes, man's closest relatives: the chimpanzee, the gorilla, and the orangutan.The researchers employed for the first time in this type of study a well-known type of statistical calculation, named the hidden Markov model which was developed in the 1960s and till now used only to speech recognition, reaching this different result about human differentiation. "Assuming orangutan divergence 18 million years ago, speciation time of human and chimpanzee is consistently around 4 million years ago. Primate evolution is a central topic in biology, and much information can be obtained from DNA sequence data," said Dr. Asger Hobolth of North Carolina State University.Each species has a molecular clock recording the speed at which DNA mutations occur. The speed may not be constant, but over large periods of time it evens, so in millennia the average is constant. The team focused on four DNA zones of the human, chimpanzee and gorilla.The results disagree with other investigations, showing that in just 400,000 years the human lineage split off from the common chimp-human ancestor.In May 2006, David Reich of the Broad Institute at the Massachusetts Institute of Technology and Harvard Medical School’s Department of Genetics got similar results for the splitting age (4 million years), but his team finally chose a 5.4 million years old for the divergence.Reich’s genetic analysis research rose the hypothesis that the early human ancestors and the chimp's ancestors could have interbred freely long after their separation. Another 2006 research made at the Georgia Institute of Technology discovered genetic evidence that, in fact, chimpanzees are closer to humans than to gorillas and orangutans.The molecular clock revealed that humans evolved one unique feature just a million years ago: our longer lifespan and our longer childhood, humans maturing sexually extremely late compared to apes.

Thursday, July 17, 2008

The World's Oldest Known Child Mystery

The remains of a 3-years old female of Australopithecus afarensis in the arid badlands of Afar (Ethiopia) at the Dikika site sandstones are those of the world oldest known child. The area is perhaps best known for turning up "Lucy," the 3.2 million-year-old skeleton of an adult female of the same species. The child, named Selam, lived 3.3 million years ago.The skull - of a monkey skull size - was spotted from a dusty slope in December 2000. The smooth brow and short canine teeth were typical for a hominid. Selam's discovery is reported in Nature by Zeresenay Alemseged, paleontologist at Max-Planck-Institute for Evolutionary Research in Leipzig, Germany; Fred Spoor, professor of evolutionary anatomy at University College London, and others.Researchers have spent five painstaking years removing the bones from sandstone, and to finish removing the sandstone from the child's bones will take several more years. Because it is very well preserved, the body may have been buried by sand and gravel in a flood. "It was buried just after it died," Zeresenay said. "That's why we found an almost complete skeleton, so maybe [drowning] could be the cause of its demise." Researchers hope this skeleton, because of its completeness, can provide much more information on details that Lucy and similar fossils couldn't. "Selam includes the complete skull, including an impression of the brain and the lower jaw, all the vertebrae from the
neck to just below the torso, all the ribs, both shoulder blades and both collarbones, the right elbow and part of a hand, both knees and much of both shin and thigh bones. One foot is almost complete, providing the first time scientists have found an afarensis foot with the bones still positioned as they were in life".The age of death makes the find especially useful, scientists say, providing insights into the growth and development of human ancestors. "It will teach us how our early ancestors grew up," Spoor said. "The only way you can evolve from one type of species into another is by growing up in a different way, because that's how you change." For instance, a prolonged, dependent childhood allowed later human species to grow larger brains, which need more time to develop after birth. While the adult A. afarensis had a brain slightly larger than a chimpanzee's, Selam's brain appears to have been smaller than a chimp's of the same age. This raises the possibility that A. afarensis experienced a more human-like pattern of brain growth. "For the first time we have insights that they may have grown their brains a little bit slower than your average chimp," Spoor said. "If you take more time to form your brain, it may well be that you make more intricate connections inside," the researcher added. "Or it may not be a positive thing—perhaps you live on poorer food or are a bit behind." Spoor favors the latter explanation in the case of these early hominids. "They haven't progressed over great apes at all, they've just changed their locomotion for whatever reason, but they were not necessarily any more clever than chimps were." "Selam also revealed just the second hyoid bone to be recovered from any human ancestor. This tiny bone, which attaches to the tongue muscles, is very chimp-like in the new specimen", Spoor said.While that doesn't directly reveal anything about language, it does suggest that whatever sounds afarensis made "would appeal more to a chimpanzee mother than a human mother," Spoor said.Selam already possessed the characteristics of her species. Scientists are especially interested in traits linked to locomotion. Selam supports the theory that A. afarensis walked upright on two legs, but also that early humans hadn't completely left the trees by that time. Scientists are excited to see how will Selam's foot look when fully excavated: human-like or chimp-like ?Scholars agree that A. afarensis was a creature that got around capably on two legs. But in the 1980s started the debate over whether the species was also adapted for life in the trees. Whereas A. afarensis has clear adaptations to bipedal walking in its lower body, its upper body exhibits a number of ape-like features, as Selam revealed. One camp held that A. afarensis had transitioned fully to terrestrial life, and that the tree-friendly features of the upper body were just evolutionary baggage handed down from an arboreal ancestor. The other side contended that if A. afarensis had retained those traits for hundreds of thousands of years, then tree-climbing must have still formed an important part of its locomotion. Like adult A. afarensis, Selam had long, curved fingers. But the shoulder blades, previously unknown for this species, are more like those of a gorilla, even if they present some human traits. The balance part of the inner ear is similar to that of the apes. This could indicate that A. afarensis was not as fast and agile on two legs as we modern humans are. The neck seems short and thick - like a great ape's - rather than the more slender human type. This limited the ability to decouple its head and torso, which play a key role in endurance running in our own species, keeping the head stable while running. "It's not out of the realm of possibility that they were still exploiting some of the arboreal habitats for getting off the ground at night and sleeping up there, or going back to familiar food sources." said Donald C. Johanson, Lucy's discoverer. C. Owen Lovejoy of Kent State University disputes the assertion that the scapula looks like that of a gorilla. "It's primitive, but it's really more humanlike than gorillalike" says Lovejoy, a leading proponent of the idea that A. afarensis was a dedicated biped.The discovery of the famed Laetoli footprints in 1978 closed the debate, he states. That trail showed that A. afarensis did not have a grasping big toe. Lacking that prehensile toe, Lovejoy says, A. afarensis could not move about effectively in the trees. Selam is a " good example of mosaic evolution". " It looks like natural selection is selecting for bipedalism in the lower limb and pelvis first, and things that are not really used in bipedal locomotion, such as arms and shoulders, change at a later stage", says Johanson. The skull also shows a mixture of traits, with its primitive hyoid bone, and human pattern of brain growth. Once, the region where afarensis lived was much wetter, with lush woods and grasslands with a savanna fauna, as nearby excavated fossils showed.

Tuesday, July 15, 2008

The Mystery Of Earliest Human Settlements In Russia

The discoveries made at an archaeological site on the banks of the River Don in southern Russia revealed for scientists the earliest known settlement of modern humans in Europe, dated 45,000 years ago.The artifacts were covered by sediments including a layer of volcanic ash from an eruption in Italy dated to about 40,000 years ago, thus the site must have been inhabited a few millennia earlier.

"The team, led by the Russian Academy of Sciences and the University of Colorado at Boulder, founs stone, bone and ivory tools under ancient volcanic ash on the Don river in Russia 400 km (250 miles) south of Moscow, " said John Hoffecker , a fellow of the school's Institute of Arctic and Alpine Research.

The site also contained perforated shell ornaments, which must have been achieved from the Black Sea coast, some 300 miles (500 km) south, and a carved piece of mammoth ivory apparently the head of a small human figurine. "It could represent the earliest known piece of figurative art in the world," said Hoffecker. "The big surprise here is the very early presence of modern humans in one of the coldest, driest places in Europe," Hoffecker said. "It is one of the last places we would have expected people from Africa to occupy first." Neanderthal people were known to have inhabited Europe for 300,000 years, before the arrival of modern humans, but - undoubtedly - the Kostenki site was inhabited by Homo sapiens. "Although human skeletal remains in the earliest level of the excavation are confined to isolated teeth, which are notoriously difficult to assign to specific human types, the artifacts are unmistakably the work of modern humans," Hoffecker added. "Unlike the Neanderthals, modern humans had the ability to devise new technologies for coping with cold climates and less than abundant food resources," he said. "The Neanderthals, who had occupied Europe for more than 200,000 years, seem to have left the back door open for modern humans," he added.At Kostenki a group of 20 sites was excavated for decades. In the past, Kostenki "yielded anatomically modern human bones and artifacts dating between 30,000 and 40,000 years old, including the oldest firmly dated bone and ivory needles with eyelets that indicate the early inhabitants were tailoring animal furs to help them survive the harsh climate," the researchers said. Other artifacts discovered included simple tools such as drills and awls, and a spade made from antlers, but the site also harbored bones of prehistoric animals such as woolly rhinoceros, bison, mammoth and moose. Worldwide, the oldest proof of modern humans outside of Africa comes from Australia and dates 50,000 years back.This discovery from Russia pleads for a relative early migration out of Africa, earlier than 50,000 years ago.

Wednesday, July 2, 2008

The Mysterious Protein That Revolutionized Insect Sight

A compound eye is a visual organ found in insects and some crustaceans.Such an eye has 12 to 1,000 ommatidia. These are tiny sensors that distinguish between brightness and darkness, and sometimes can detect color, and structurally correspond to the ocular globe of the vertebrates. The image perceived by the arthropod
is a combination of inputs from the numerous ommatidia, which are oriented to point in slightly different directions. Unlike other types of eyes, a compound eye does not have a central lens or retina, resulting in poor image resolution; however, it can detect fast movement (flies) and, in some cases, the polarization of light (bees). Each ommatidium consists of a lens and several visual receptor cells parallel to each other or slightly twisted. Recently, a team of biologists at the University of California, San Diego have discovered that the presence of a protein in the compound eyes of the fruit fly (photo)(which glow at center due to a fluorescent protein) enables the formation of distinct light gathering units in each of its 800 ommatidia. This evolutionary "open system" enabled insects to make significant improvements in visual acuity and angular sensitivity. Most insects, like beetles, bees and mosquitoes (which are in fact primitive flies) species have the light-gathering units fused together into a "closed system."One of three proteins needed to form these light gathering units is present in the visual system of fruit flies, house flies and other insects with open eye systems, but conspicuously absent in species with closed systems. The loss of this protein, called "spacemaker," can convert the eyes of fruitflies—which normally have open eye systems—into a closed one. In contrast, the introduction of spacemaker into eyes with a closed system transformed them into an open one. "These results help illustrate the beauty and power of evolution and show how ‘little steps’—like the presence of a single structural protein—can so spectacularly account for major changes in form and function," said Charles Zuker, a professor of biology and neurosciences at UCSD.

Friday, June 27, 2008

The Mystery Of First Human Embryo Clones

A cloned Scarlet Johanson may be the dream of any man and a Californian company has just made the first step toward this purpose: for the first time, scientists have achieved cloned human embryos using DNA extracted from adult skin cells, as reported in the Stem Cells journal. "That's an important first step toward generating embryonic stem (ES) cell lines from such embryos, which can be used to study and treat diseases such as diabetes and Parkinson's," stem cell researcher George Daley of Harvard Medical School in Boston said.By achieving cloned human embryos starting with cells from patients with various diseases, researchers hope to come with new treatments using the transplant of cloned tissues and even organs.
In 2007, a team managed to turn skin cells into ES-like cells, but the real embryonic cells are more pluripotent cells that can turn into any cell type, generating any type of tissue. The team at Stemagen, a biotech company based in San Diego, operated with skin cells donated by two men and 25 eggs (oocytes) donated by women at a fertility center. The nuclei (comprising DNA) from the eggs were removed and replaced with DNA from the male skin. "Two of the eggs became 5-day-old embryos, or blastocysts, that were clones of the male donors. That's an "unexpectedly high" success rate," the company said in a statement. "The key to the team's success was utilizing fresh, mature oocytes from females of proven fertility," lead researcher Andrew French said. Double DNA analysis showed that two of the blastocysts possessed the DNA of the male donor cells. The mitochondrial DNA was clearly from the oocyte while the nuclear DNA from the male skin. The goal of the researches is to extract ES cells from the inner cell mass of cloned blastocysts and create a new cell line from them; this will eliminate any doubt concerning the method's effectiveness. Those ES cells could be used in treatments. Some doubt that this could be so easily achieved, pointing to the presence of chromosomal abnormalities in the achieved embryos. "The blastocysts in the paper look very unhealthy. I would guess these clones are abnormal, too." said Robert Lanza of Advanced Cell Technology in Worcester, Massachusetts. Andrew French responded that the donor clinic "has got pregnancies from IVF [in vitro fertilization] embryos that look similar." Two months ago, another team achieved ES cells from cloned monkey blastocysts, a first in the case of primates.