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Chapter 981 People

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    ?

    Although Chu Lihua was not completely attracted, she nodded seriously, only to hear Liu Xingting continue, "Yes, this is a fundamental difference.

    Not only do all mammals with feet usually land on all fours, even among the approximately 250 species of primates, we humans are the only ones who have chosen the strange way of being on two feet for a long time.

    Some researchers argue that bipedalism is a defining human characteristic, no less important than our brains.

    Landing on two feet is a remarkable change.  There are many theories to explain this. For example, standing upright can make people free their hands to hold children or use tools, or standing upright will make them taller and have a better view, or standing upright with two feet can make people learn to throw, etc., but in the end  For what reason, we are not yet sure.

    In any case, we know that humans began to waddle about six million years ago, and finally learned to run long distances about two million years ago.  With the ability of long-distance running, human beings have started a hunting career for more than one million years.

    During the long process of human beings starting to walk upright, a series of changes have taken place in the body structure.  Our necks became longer and straighter, connecting to the center of the skull rather than to the back of the skull as in cats, dogs and apes.

    Our spines start to get softer, our knees get bigger, and our thighbones get thicker and tilt inward.

    The structural changes in the thigh allow us to walk more smoothly and run more easily to maintain balance.

    And even our close relatives, primates, can't walk like humans even after training. Their bone structure is different from ours.  This makes them wobble and move slowly when walking on two legs.

    To move like humans on the ground, chimpanzees use four times more energy than humans.

    Landing on both feet also means the redistribution of weight.  Back pain and lumbar herniated discs are uniquely human problems due to weight redistribution.

    However, it is also obvious that the back pain and herniated disc are worth it, and the benefits in exchange for two feet are greater.

    After all, after learning to walk and run on two legs, humans will be able to hunt big animals, and finally be able to eat meat.

    Probably because hunting brought more energy-dense meat food, and the brain was fully developed. Humans finally learned to use stones to make tools 500,000 years ago, and began to transform natural objects into artificial objects.  I learned to use fire a few years ago, and I can cook food before eating.  "

    The more Liu Xingting talked, the more he got into the mood. The two nurses and one doctor in the ambulance began to listen carefully, nodding their heads in agreement from time to time.

    At this time, Liu Xingting is of course more serious, "During this process, human hands also began to become different. Our thumb can touch other fingers, this is what we call 'opposite thumb', that is,  Say the thumb is opposite the other four fingers for a grip.

    Neither cats nor dogs have opposable thumbs, but most primates do.  It's just that unlike other primates, we also have three special small muscles in our thumbs, which are unique to humans.

    These three small muscles work together to allow humans to grasp and manipulate tools with firmness and dexterity.  Although most people have never heard of them, these three little muscles are arguably at the heart of human civilization.  "

    Not to mention, Liu Xingting stretched out his hand and made a gesture of grasping.

    Chu Lihua involuntarily followed suit, indeed.

    Others also tried and nodded in agreement.

    After the demonstration, Liu Xingting continued, "In addition to the hands, the development of the brain and learning how to use fire are also two major events that affect the human body structure.

    Let's talk about the brain first.  The brain is a hungry organ, it makes up only 2% of our body weight, but consumes 20% of our energy.

    And for newborns, because the brain is developing rapidly, about 65% of the energy will be used.  That's why babies are always sleeping.

    But the strange thing is, we don't need such a big brain.  We don¡¯t need to be able to compose music or discuss philosophy, or understand calculus, just to survive on Earth.

    After all, if we are only alive, we only need to be a little smarter than our prey.  And the brain consumes so much energy and takes up so much space that our skulls are so different from those of other primates.

    We've also grown a large frontal lobe ¡ª¡ª the chunk of the brain behind our forehead that's dedicated to processing complex information and generating reason.

    The brains of our ancestors were even bigger than ours. The human brain 10,000 years ago was bigger than the brain of today.A human brain is about the size of a tennis ball.

    As for why the brain shrinks, we don't know yet.

    But in short, when people have bigger brains, life becomes better.  Human beings have learned to use fire to cook food and eat cooked food.

    Cooked food is easier to digest, easier to chew, and less prone to germs and parasites.  The nutrition of cooked food is easier to absorb, which also saves us a lot of time.

    Other primates spend up to seven hours a day just chewing food.  And the eating time saved by human beings can be used to develop culture and entertainment;

    For example, tell stories around the campfire, or draw some pictures in the cave.  The germination of human civilization was born in this way.  "

    Chu Lihua really had a brief investment this time. Her "why are people human" was a sentimental expression because of too much pain. She did not expect Liu Xingting to deliberately deviate from the meaning.

    Fortunately, the effect is still obvious.

    Seeing that Chu Lihua's state has changed.  Deep down in Liu Xingting's heart, he was relieved that his hard work was not in vain.

    Therefore, the talk is more detailed, "The impact of cooked food on human beings is also reflected in the body structure.

    Because no longer need to chew food hard, human teeth began to shrink, the lower jaw receded, and the space in the entire mouth became smaller.

    For modern people, the most intuitive impact of this change is the wisdom teeth that are often painful.  Those teeth originally had room to grow, but because the space in the mouth of modern people has become smaller, the teeth that should have grown can only be squeezed out barely, crowding other teeth in a mess, and often causing a series of inflammation and pain.  pain.  "

    Hearing this, Chu Lihua touched the lower part of her cheek unconsciously, the toothache at the end was really fatal!

    It turned out to be the reason for evolution, but obviously this evolution has brought a lot of pain to people.

    I often accidentally hurt the tender meat in my mouth because of chewing, that kind of pain!  It's beyond words!  (Remember the site URL: www.hlnovel.com
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