what kind of natural pressure could have selected for these caracteristics or traits? two potential answers?
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.
501189
Gymnosperms are generally wind-pollinated, which puts pressure on them to be taller. Angiosperms have more options available, so the selection pressure would be less. Water is always conducted by capillary pressure, but in the tallest trees water from the roots is augmented by water vapor collected from the air through stomata in the needles/leaves.
21700
Stress is simply a fact of nature -- forces from the outside worldaffecting the individual. Hence, all living creatures are in a constant interchange with their surroundings (the ecosystem), both physically and behaviorally. This interplay of forces, or energy, is of course present in the relationships between all matter in the universe, whether they are living(animate) or not living (inanimate). However, there are critical differences inhow different living creatures relate to their environment. These differences have far reaching consequences for survival. Because of the over abundance ofstress in our modern lives, we usually think of stress as a negative experience.But from a biological point of view, stress can be neutral, negative, orpositive. \n\nStress has driven evolutionary change (the development and natural selectionof species over time). Thus, the species that adapted best to the causes ofstress (stressors) have survived and evolved into the plant and animal kingdoms we now observe. Man, because of the evolution of the human brain, especially thepart called the neo-cortex, is the most adaptive creature on the planet. This adaptability is largely due to the changes and stressors that we have faced and mastered. Therefore, we, unlike other animals, can live in any climate orecosystem, at various altitudes, and avoid the danger of predators. Moreover, most recently, we have learned to live in the air, under the sea, and even inspace, where no living creatures that we know of have ever survived. So then,what is so wrong with stress?\n\nA brief history of stress\nA key to the understanding of the negative aspects of stress is the conceptof milieu interiur (the internal environment of the body), which was first advanced by the great French physiologist, Claude Bernard. In this concept, he described the principles of dynamic equilibrium. In dynamic equilibrium, constancy, a steady state (situation) in the internal bodily environment, is essential to survival. Therefore, external changes in the environment or external forces that change the internal balance must be reacted to and compensated for if the organism was to survive. Examples of such external forces include temperature, oxygen concentration in the air, the expenditure of energy, and the presence of predators. In addition, diseases were also stressors that threatened the constancy of the milieu interiur.
216288
When you were born does not determine your traits.  Heredity and environment determine your traits.  Astrology is mythology, and is useless in determine how a person will be, what will happen to them, or who they are compatable with.
111422
Come on, you've got to do SOME leg work here.  Those are huge subject areas.  Where would we start?\n\nOK, Darwin: Natural selection acts on random variation.\n\nLamark: Acquired characteristics can be passed on to the next generation.
221900
Because genes influenced by millions of evolutionary years, environmental conditions and selective preference made us that way!\n\nP.S. I think your picture pose is way cute, will you blow it up so we can see you better?  :-)
1114940
Pressure can't be associated with a direction coz it is directed in many directions simultaneously. Weight is a vector coz it the gravitational pull that  is always directed towards th centre of earth.
483536
A very easy example is the generation and regulation of radiant heat by the body. If your ancestors are from cold climates, (mine are from Scotland) your body will usually react better to cold, and you would be more comfortable in lower temps. than a person whose ancestry is from the Equator. Naturally, training and acclimation will blur the results somewhat, but if you look at the members of the Army stationed in the Arctic, most have cold-weather ancestry. This is despite our technology and building practices. DNA controls metabolic rate, and is subject to evolutionary mutation.
474523
There are some great maps out there correlating skin tone with a modeled optimum at each geographic point.  That optimum is based on balancing the need to avoid burning and skin cancer against the need to obtain UV light for creation of vitamin D.  \n\nOther adaptations relate to features of the environment.  Northern Europeans, Inuit, and Eskimo people have a distribution of fat on their bodies that is optimized for heat retention.  The body shape of a Masai, for example, would be less than optimal near the North Pole.\n\nThere is a hypothesis that many traits are associated with sexual selection or may pertain to the tradeoff between sexual selection and aspects of the environment.  The distribution of fat tissue, particularly in women, in different races has been proposed as correlated with cultural differences in male preference as well as with adaptaion to the local environment.\n\nFinally, there is the feature of accident.  The epicanthal fold of many East Asians might have been beneficial to many Caucasians, but perhaps by chance the feature simply wasn't present in founding populations in Europe.  Characteristics in founding population and gained or lost by chance certainly play a big role in differences in humans from different geographic areas.  Not everythig is adaptive.\n\nBear in mind that this is not based on fixed differences among populations or races of humans, but instead on gene frequency in different populations.  For example, Swedes are lighter in skin color than the Ndebele not because each population has distinct genes, but because those genes differ in frequency.  Among all the loci that contribute to skin color, Swedish populations have very few alleles that code for dark skin.  Each individual Swede will therefore have only a few dark loci where dark alleles are present whereas most loci will have light alleles.  The Ndebele populations and individuals would act in reverse.
12704
Glenn, I appologize if this comes off pretentious, but I would like to address part of your question. Unfortunately, it's not the part you probably want answered, but I feel it's the most important part of your question.\n\nWhen it comes to biology/evolution, to ask the question "why" is unanswerable. It's not the way things work when it comes to evolution. Things are the way the are now because of millions of years of selective pressures dictated all current living things into their current constructions.\n\nIn fact, the question "why" is nearly impossible to even consider when it comes to biology. Things are the way they are not for any particular reason. Maybe there were organisms that had developed a large "blowhole" like structure that was at the end of their nasal cavity. But for whatever reason, which may or may not had anything to do with the having two small nares or a bigger blowhole, environmental pressures allowed one organism to succeed and pass along their traits (including the nairs) and the other became extinct.\n\nWe can talk about structure's function that it provides, but that structure was in no way "designed" that way to provide that function. In fact that function may or may not have been essential to that organism surviving and passing along that trait. Some traits are simply along for the ride. In those cases it's other structures that provide increased fitness which allows certain organisms to outcompete and prosper through evolutionary time. \n\nIn the case of having two nares at the opening of the nasal cavity, I have no idea if this was a critical structure for the propogation of organisms on earth. I can make the guess, however, based on the fact that many animals do have similar structures, that this feature was present early on in evolutionary time. The fact that this trait has been maintained suggests one of two possibilites: either these stuctures do have some level of importance for organisms' fitness or 2) there is no real pressure otherwise that has forced a change from this trait that developed early on.\n\nIf there have been some insight gained which is true, I'm not aware. Hopefully someone who has that expertise will find your question and answer. In the meantime, I hope you will consider why the word "why" is not an appropriate place to start the path to finding out.
754576
Power. \n\nI think it's a family trait.
966025
I think it would help your paper to say why you think each of these things might occur, and even add some references that support your reasoning. You might be interested in the "Trends in Evolution" part of the web page I have linked at the bottom to help your make predictions.\n\nWhy do you think sexual dimorphism would change in the future, and why would it get more apparent if sexual roles are becoming more equal? (in general sexual dimorphism has been decreasing in human evolution - see link below, about 2/3 of the way down the page)\n\nWhy do you predict they will get taller (this is a good prediction, by the way, but why do you think it to be true)? \n\nIs there any reason to think that ESP or telekinesis will become possible?? (probably not, in my opinion, but what data can you find that says one way or the other)? \n\nIf you have read something that supports what you are saying, and you can provide references in the paper, your arguments will be much stronger - increasing the probability of a good grade!!
109372
Good question. \nAny candidate for a pre-biotic existence should have possessed the characteristics that make evolution possible, that is: \n- genetic information (heritable instructions)\n- ability to replicate and carry out those instructions\n- replication with some random variation (so that new traits could appear)\n\nThe "prebiotic RNA world" is one possible theory.\nThis hypothesis was independently proposed by Carl Woese,  Francis Crick, and Leslie Orgel. If you're interested go to the link, it's clear and well explained.
787927
Every system is capable of change.  These changes are subject to both internal and external pressures that require a being to adapt.  For example, an internal pressure that would require a change would be the sexual maturation of an organism.  An external pressure that could cause a change would be something like a significant temperature change, or a change in predation patterns.
676046
The interaction between an organism and its enviroment is dynamic. It is impossible to separate the "nature" from the "nurture" because they are intertwined. Unfortunately, many people including scientists are too caught up in this false dichotomy.
203146
11.B Cause\n12.C The atmosphere keeps Earth warm.\n13.B Feeding habits and migration.\n14.D While and however.\n15.A A paragraph should have one main topic.
597267
Lower pressure will result in more "convection," or vertical movement of moisture.  So in general, the lower the pressure the better chance of precipitation.