How can human beings be at the top of the food chain, when there are viruses which prey on us? arent they no.1
482984
The food (trophical) chain is based on trophical relationships between organisms (predator-pray) and viruses use human and other animals as hosts not as food. Even other parasites aren't higher than human in a food chain because it's a very complex calculation that has a lot to do with mass and number of organisms belonging to the food chain... And yes, someone was right, there are some animals that could eat a man and they could be higher in a food chain but food chain doesn't describe all the trophical relationships in nature, it's just an example! People (even teachers) often forget that...
145340
Climate and food.  \n\nNote that humans do not have any effective natural insulation against the weather, while most animals have leather, furs, feather, fat, etc.  This forced humans to find other ways to protect themselves against the weather.  We find/built shelters, make and wear clothes, and most importantly, built fires.  All thanks to our resourcefulness as a result of a highly developed brain.  \n\nHuman has never been the strongest animal when it comes to food chain.  Yet, we were able to dominate it because we developed ways to hunt and evade effectively.  We invented tools (spears, etc.) and other traps to hunt, and we learned how to build effective shelters from predators.  We were also able to developing herding and agriculture, which secured our food sources.
201870
By definition, viruses cannot replicate themselves-they do not contain the machinary to do this, and never have.  Thus, in order for a virus to replicate, it must have available some other form of life which can carry out replication.  The simplest forms of life we know are extremophiles, found in deep sea vents and places like Yellowstone...prior to this discovery, it was thought cyanobacteria were the simplest.  At any rate, both extremophiles and cyanopacteria are forms of bacteria, and each has viruses that infect them- Since viurses depend on bacteria for replication, but bacteria do not depend on viruses, bacteria must have come first.  If a lonely virus did evolve before anything else, it would have degenerated without progeny.  BTW, biologists do not consider viruses "alive" because they cannot replicate...but again, thats just a human definition.
129956
listen to t. h. white (sword in the stone author). we will in the end use up all our resources and the organisms that need them will die. it will break off part of the food chain and no other organisms will be able to live. the part of that is what happened to the dinosaurs (likely) and it will probably happen to humans considering how destructive we are.
254869
Viruses mutate.  What is a harmless virus today could change a gene-pair on its DNA and be a real killer tomorrow...  Same reason some diseases go away - like the flu pandemic that killed millions in 1918 or so - we haven't seen it since.\n\nThis is what is scary about the bird flu - right now humans only get it from direct contact with infected birds - that would mena that since most of us do not raise our own fowl anymore most of us were safe, right?  Wrong... If a person has it, and it mutates in that person's body to allow person-to-person transmission, the human population is at risk from other humans... and if it is spread easily, it could be huge.
466368
Makes sense, right? God created AIDs to kill 38 million people, and most of them being Christians?\n\nAdaptation - otherwise, there would be very little malaria, flu, and other illnesses in the world. Viruses especially are hard to cure.\n\nTo respond to the girl below: being on top of the food chain has nothing to do with diseases. All animals suffer from diseases. \n\nWhy are our best minds not able to eliminate all diseases? I would like for preachers and evangelists to come up with cures, please.\n\nSure, God created "S-E-X", but what about children who got AIDs from their parents? Sure, it's their parents' fault but not their own, so why should they suffer?
143228
If we're talking about humans, 0! We can't digest cellulose. If we're counting bacteria in termites in comsumption... Then it is a totally different question...
198504
there's a chance that a highly infectious disease with a long enough period of incubation could travel enough via its hosts to kill a lot of people. I don't know if it would be able to kill everyone though, it seems unlikely.
867049
They dont, birds do. Humans can not catch a virus from birds tho, so there has to be a middleman (well pig). Birds give the virus to hogs, who then with a little twist of the virus give it to humans (hence the first name of swine flew). The best place for this to happen is a place that has both foul & pigs (a farm) so that is why you always hear about chickens & ducks (but it can be any bird).
415464
Viruses need to be inside of a  host cell (human, bacteria, plant etc.) to reproduce. So to get inside the host they have surface proteins (sticking out of a lipid bilayer-just like most mammalian cells) that are able to trick the host cell into letting it inside, that's where it does the damage to the host. ---To simplify the virus needs to have a Protein Coating that is similar to the Protein Receptors on its host cell in order to infect it.---
1084390
Viruses must take over an organisms cells to reproduce more viruses. When the cell machinery the virus hijacks to reproduce makes a mistake when making the viruses genetic code (either DNA or RNA depending on the virus) it is called a mutation.\n\nAny time a piece of genetic information gets transcribed incorrectly, or changes due to outside influence (radiation for example) it is called a mutation. Most mutations are harmful, but sometimes a mutation turns out to be beneficial to an organism, or in this case virus which isn't actually alive (that's a whole other question). When it is said that a "virus has mutated" it can mean several things, sometimes it's as simple as a change to the viruses protein shell, called a capsid. Specifically, what scientists are worried about in a H5N1 mutation is a mutation that changes the virus receptor proteins. Receptor proteins are the part of a virus that allows it to attach and attack other cells, these receptors have special shapes, like a key, and only can attach to cells that have a corresponding shape. A good example of this is a Rhino virus, or the common cold, cold viruses have receptor proteins that attack the nasal tissue in humans, which is why it causes that particular type of infection. \n\nMost viruses start out infecting a particular species, the worry with H5N1 is that it will mutate into a form that is easily transmittable between humans, instead of birds. H5N1 appears to be a particularly deadly form of flu, if something like this happened, millions upon millions of people would die. Even countries like the US would be unable to care for all the sick people. This nasty kind of infections happen every once and while, the last really bad one, H1N1, in 1918 killed 50-100 million people.
659354
Dead plants and animals cannot be said to occupy a level in the food chain as being dead they are not able to eat and therefore occupy the lowest space on the trophic level  as food for fungus, microbes, insects, animals and other plant life.\n\nStrange question.
135333
Humans are the highest life form on Earth because we are the most complex. The fact that you are even asking this question proves that. Do you think any kangaroos are hopping around thinking, "Why are HUMANS the highest life form?" \nWe were given abilities and gifts (or we evolved) that set us apart from other life forms. I think cognitive skills are the main difference. Yes, a mosquito could transmit a virus that could kill a human, but once a problem is recognized, human beings have the capacity to solve it. In this situation, a vaccine could be developed and problem solved. No other life form on Earth has that ability.\n\nPS: You look gahjus in the new pic!
438655
Some viruses are not specific to animals or to humans and can be passed back and forth.  For example, the avian flu.  \nAlso, horses are susceptible to many human ailments.  These viruses are transferred just like any virus, through ingestion of some sort.  This means you breath it in if it is a virus that can survive while airborne, or you can eat it, drink it or get it into your body through sores or sensitive areas like your eyes or "other areas"(HIV).  Say an animal is sick and you kill it and eat it.  Maybe the virus withstands great heat and cooking the meat of the infected animal doesn't kill it.  Eating the meat will pass the virus.  You could touch the sick animal, get contaminated saliva on your hands and then you touch your mouth or eyes; you will get sick. \n\nMost viruses are specific to certain species though.  An animal virus only affects animals and a human virus only affects humans.  Still these viruses can mutate into a virus that affects humans and animals.  That is what is so scary about viruses.  They multiply quickly and mutations are very common.
775996
They can be.  Some viruses are harder to kill then others.  I f viruses can't be killed, we would die of a simple cold.  Some viruses  are like roaches,  You could smash the ones you find, but they breed faster than you could kill them.  Others, like Herpes are attacked by our bodies defense until the virus is under control.  The remaining viruses hided where our defenses can't attack or find them.  When our defenses weekend, they come out again.  Others are like HIV.  Your body can kill them, but if the virus are able to make a foothold in our body, it attacks our immune system, therefor our body can't kill them anymore.
246832
Most systems, when left alone, will tend to come to a "steady state" or be at rest.  In the case of balancing the ecosystem, overpopulation is a situation that I tend to think would eventually be controlled by the environment.\n\nAs an example, consider bacteria and viruses for which not everyone is immune nor is there necessarily a vaccine.  The increase in population ensures: a) that there are more hosts for these agents to travel; and b) that the agent doesn't have that far to travel, so it does so quickly.  Epidemics have a way of balancing out overpopulation.\n\nIn some cases, people make the mistake of introducing some 'agents' (not necessarily viruses, but such as in a recent case with toads) into an environment in which they help control the population in one aspect, but then the agent itself overpopulates.  Eventually, as it runs out of food (unless it has several plentiful sources in the environment to which it's been transplanted) it too will experience a loss in population.
527102
Zombies, by their true definition, feed on brains and are... undead.\n\nSure you can say that such a virus could happen and make humans revert to animalistic state, but... what animals do you know that eat each other.