Why don't snakes have arms?
956120
Snakes can't tell time, so they don't need a wristwatch, hence they don't have arms.
670924
Birds have one, snakes have one, and i believe a few of the lizards only have one.
600843
most amphibians have legs so they can walk on land. there arent usually amphibians that dont have legs...
309101
They don't have a nervous system.  They do have chemical and tactile sensors, as well as chemical messengers that cause actions in response to stimuli.  For example, a mimosa plant will fold up in an attempt to protect itself if touch it with your finger.
431352
Snakes lost their legs on land, not in the sea as previous scientists thought, according to new research by professor of biology S. Blair Hedges and postdoctoral fellow Nicolas Vidal.\n\n"Everyone agrees that snakes evolved from lizards and are close relatives to lizards," Hedges said. "What is controversial is the specific group, whether on the land or in the sea."\n\nScientists estimate that snakes evolved 150 million years ago, Vidal said. For many years, they believed in the terrestrial or land theory, which says that snakes evolved from lizards that burrowed underground.\n\nThen, seven years ago, the discovery of a fossilized marine snake with tiny hind legs fueled the marine hypothesis that snakes lost their legs in the sea. The marine snakes called mosasaurs are now extinct, but their closest cousins, the monitor lizards such as the Komodo Dragon, are still alive today.\n\nHedges and Vidal chose two genes and compared them in lizards and snakes to see how closely they are related. From statistical analysis of these gene sequences, they created a family tree.\n\n"These two genes have accumulated different mutations in the different species," Vidal said. "These differences between the species are used to build the evolutionary trees. Snakes are not closely related to the monitor lizards, which means that they cannot have marine origins."\n\nHedges and Vidal's research is significant because of the comprehensive scope of the snakes and lizards studied. They collected DNA from 64 species representing all 19 families of living lizards and 17 of the 25 families of living snakes, Vidal said.\n\n"We mostly acquired DNA from the soft tissues, blood, shed skin, scales and tips of the tails of the animals," he said. "A very small amount is needed, so we can get the sample without killing the animal."\n\nHedges and Vidal acquired samples from other colleagues, their own collections, fieldwork in South America and pet stores that trade exotic animals, Hedges said.\n\nSome of the samples were difficult to acquire because some snakes and lizards are limited to certain parts of the world, such as remote islands, but it was crucial to their study.\n\n"We felt it was important to analyze genes from all the lizard groups, because almost every lizard family has been suggested as being the one most closely related to snakes," Hedges said. "If we had failed to include genes from even one of the lizard families, we could have missed getting the right answer."\n\nA possible theory to explain why snakes dropped their legs on land is that limbs are not conducive to their burrowing habits, Vidal said.\n\n"The idea is that if you have limbs sticking out, it's difficult to get into small openings," Hedges said. "It's more advantageous, because it enables snakes to get more food and offers safety from predators."\n\nHedges and Vidal did not find the closest lizard relative to snakes, but they did succeed in eliminating the monitor and marine lizards as possibilities.\n\n"This study doesn't answer all the questions," Hedges said. "In most fields, questions aren't answered all at once. They're answered in increments, and in this study, we've ruled out the marine theory, but that still leaves a lot of possibilities."\n\nHedges and Vidal said they hope to find the closest relative to snakes in the next year.\n\n"The work by Dr. Hedges and Dr. Vidal is a tremendous contribution to the body of knowledge," said Bryan Fry, deputy director of the Australian Venom Research Unit at the University of Melbourne in Australia. "Their data provides strong evidence for the terrestrial loss of limbs."
877429
Assuming it's true, then it's probably because of creatures' abilities to adapt to their environments.  Over centuries, evolution and genetic mutations and such allow different species to form, to become most suitable for their habitat.\n\nHowever, I'm a bit doubtful that a snake, a cold-blooded animal, would be able to survive in such a cold region....
420898
Has to do with how the limbs develop in the first place during embryogenesis.  In the octopus, the limbs likely just grow outward from the body (same as for a lizard's tail).\n\nIn humans your limbs do not grow outward from the body.  They develop in a much more complex process during the initial stages of body development that cannot be repeated because the body is never again in such a primitive stage.
1172981
Because there was no midway for hardly anything. Lizards never where halfway between lizard and bird, invertabrae never had a halfway formed spine, apes where never halfway man. Thats the only reason I can think ;)
494185
most mammals have four appendages, they just evolved differently. humans evolved into arms and legs with very different uses. rodent type animals have front feet they can use as hands, as do most monkeys. beasts of burden and their predators maintained four legs for obvious reasons.
399423
Snakes, lizards and amphisbaena (which most of you won't have heard of, but they're neat!) have "hemipenes", basically dual penises.  It has no real advantage, it's just how they evolved.  They only use one at a time.  It's just a different way to evolve a penis structure on a bilaterally symmetrical animal.
170773
Oh great another question with multiple answers by people who have no fricken’ idea what they are talking about.\n\n>>>>How come there are an abundant found\n>>>> species of snakes in Australia, but no snakes\n>>>>> in Hawaii?\n\nFirst off lets clear up the common misconception that there are no snakes in Hawaii. There are no LAND snakes in Hawaii. There most certainly are sea snakes in Hawaii.\nThere are no LAND snakes in Hawaii because Hawaii has only existed for the blink of an eye in geological time. Because it is so new all the animals and plants in Hawaii have had to arrive there by travelling across the ocean from nearby landmasses. Hawaii is far too far away from the nearest landmass with snakes for land snakes to be able them to swim that distance.  \n\nFor the same reason Hawaii also has no native land reptiles, amphibians or land mammals of any kind.  Several species of reptiles and mammals have hitched rides with people or been deliberately introduced to the islands, but so far no snakes.\n\nIn contrast Australia as old as any landmass on Earth. snakes evolved in or near Australia when it was still part of the supercontinents. \n\n______________________\nGuelph said “During the last ice age, sea levels were low enough that\n>>>>>>> the Indonesian islands formed a virtual landbridge to Australia.\n\nThere was no land bridge, virtual or otherwise. More importantly snakes and their ancestors have been present in Australia since before it split from Gondwana. No land bridge was needed or used.\n\nKari said “Snakes may have been brought into Australia”. This is total rubbish. There are no exotic snakes living in Australia outside of zoos. No snakes have been brought into Australia. They have more than enough of their own.\n\nCeciel who is obviously a graduate of the Simpson’s school of biological control, is clearly planning to release Himalayan Mountain gorillas to Hawaii deal with the mongooses.\n\nKnowlegdeSeeker said " Colubrids, the progenitors of modern >>>>>> snakes started to show up about 36M years ago."\n\nColubrids are NOT the pregenitors of modern snakes. \n\nColubrids are one of the three major types of modern venomous snakes, the other being the elapids and viperids (See link 1 below.)Colubrids are not a very significant part of the Australian snake fauna and restricted mostly to the northern parts of the continent (see links 2 below). For that reason they are indeed believed to be fairly recent immigrants (See link 3 below).\n\nThe first snakes show up in the fossil record some 100 million years ago in South America, when, as the website you posted shows, Australia was still very much part of Gondwana. In fact the best early snake fossils all come from Gondwana (including present day Australia) and snakes were widepread across that supercontinent by the mid cretaceous, well before it broke up (See remaining links for details).\n\nAfter that the record gets patchy. In fact snakes are amongst the worst represented of all the vertebrate groups. But the general consenus amongst palaeontologists is that snakes evolved in Gondwana and radiated from there to the rest of the world. As a group they never moved into Australia unless it was form South America when the two landmasses were still connected. No land bridge required.
1107422
Is this a riddle? \nYou gave virtually no information about the animal, only that it has a tail and can climb trees.\n\nIt could be a lizard, snake, monkey...\n\nAre you thinking of the double-snake wrapped around a staff? This is the symbol of medicine, the caudecus.
761221
Bird: How does the bird's vertebra indicate that it evolved to support flying? (Answer: The thoracic vertebrae are fused to provide a rigid upper shell to withstand the muscular forces of flight muscles. As partial compensation for this rigidity, birds have more neck vertebrae than many animals to provide enough flexibility to feed, groom, etc. See ref. 1.)\nSnake: How does the snake's vertebra indicate that it evolved to support slithering? (Answer: Snakes have a large number of vertebrae, which are connected together by ball-and socket joints. These characteristics allow extreme flexibility. Together with specialized muscles, the vertebra enable the snake to move with speed and agility. See ref. 2.)
966426
The reason why it is there is that it is more efficient to have a wall. It separates oxygenated from non-oxygenated blood so only oxygenated blood is sent to muscles.\n\nAmphibians and reptiles don't have a wall separating the oxygenated from non-oxygenated blood, they are alive, but their circulatory system is less efficient because some of the blood travelling to the muscles doesn't contain any oxygen.
385063
Yes because they are reptiles.\n\nI could wax lyrical for pages and pages (see above) and you raise an excellent point about vertebrae, however thay are reptiles.
525455
If snakes evolved from land dwelling creatures, then those land dwelling creatures evolved from sea creatures.  After all, humans evolved on land.
1082915
cool question!\n\nno reptiles do not suffer from dwarfism in the true sense that humans do \n\nbut they can have retarded or stunted growth due to stress or poor food etc either when they are in the egg or subsequent to that