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Humans--- birth

Baby animals:  Why do young animals look cute to us humans?
Boy babies:  A woman expects a baby.  What is the probability of giving birth to a baby boy?
Choosing sex of babies:  I have two girl babies. But I wish a boy. Can medical science help me to born a boy baby?
No-father fertilization: Is it possible to take the chromosomes from one female egg and inject them into another female egg so they attach and actually form a fertilized egg?
Twins differ: Can my twin boys be identical if one is allergic to cow's milk and the other is not?
Twins, DNA: Do identical twins have identical DNA?
Twins trigger: In the case of identical twins, what triggers the fertilized egg to result in two embryos? What's the probability of having identical twins?
Twins, cousins & siblings:  If a set of identical twin women married a set of identical twin men and subsequently had children would their children genetically be siblings?  I think they will, my friend A.J. says I am crazy.  Help!
Twins, probability:  Does twinning run in families?

Humans--- body

Appendix:  Why do we no longer use or need our appendix?
Breathe:  How many plants are needed to produce enough oxygen for one person?
Breathe:  When SCUBA diving at 33-foot (10 m) depth, air pressure in your lungs is about twice that at sea level, which means your lungs have twice the amount of oxygen. Why can't you hold your breath twice as long?
Cells:  If I am 95 years old, do I have any cells in my body that were present when I was 3 years old? What about at conception?
Cells:  Do children's brain cells divide?
Cells:  Where do cells get energy?
Fat:  Do women really have an extra layer of fat that men don't?
Fingers: Why do we have five fingers?
Fingers:  Why do the tips of your fingers shrivel like a raisin when you stay in the water too long?
Fingernails:  What determines the speed at which fingernails grow? Do they continue grow even after we die?
Fingerprints:  Can you tell me how long fingerprints stay on or last?
Fingerprints:  When skin on fingertips grows back from injury or an accident does the fingerprint have the same pattern as before or a new pattern?
Hair:  Why do people have gray hair? Is that because of the alteration of gene expression or the loss of certain pigments?
Hair: Why does a child's hair appear "naturally" shiny? Why does lemon or vinegar improve the appearance of shine?
Hair:  Approximately, how thick is a hair strand?
Hair:  When I was born, I had blond hair, but now it is dark brown. What caused this change?
Hand: What makes the popping noise when I crack my knuckles and why can't I pop them again?
Heart:  What keeps the heart pumping all the time? A friend of mine says sometimes he is afraid that his heart will stop beating suddenly!  Does he have some reason?
Hydrogen peroxide:  How does hydrogen peroxide "know" germs when it comes into contact with them? Peroxide doesn't fizz if you pour it on uncut skin, so it's apparently not reacting to simple dirt or oils. But, it fizzes up a storm if it contacts germs, such as in an infected cut.
Recycled:  Does earth get heavier because the human population keeps increasing and the number of living things on earth keeps getting larger? If not, why not?
Size: What is considered to be the average size woman in America? The average size man?
Size:  Would you please update your 2002 average American woman size article?  What is the average size now?  Perhaps you could consider answering the question for North America?
Size:  Why is the most recent data on the average weights of Americans so outdated, when Canada's information is current to 2005?
Size:  What is considered to be the average size woman in the UK?
Size: What is the average shoe size for American women and men?
Skin: Can you get sunburned through a car windshield?
Smile vs. frown:  Do you use more muscles to frown or smile?
Spit:  Why doesn't saliva break down the tongue like it does food?
Tattoos: why do they last so long? I thought we constantly grew new skin.
Toenails:  Why are toenails thicker than fingernails?
"Useless" body parts:  Are there any body parts of a human body that we don't use?
Voice:  Why does helium change people’s voices after being inhaled?
 

Humans--- health (aging, disease, injuries)

Aging: Do you age quicker on heavier planets?
Aging, Life Span of Ancients: I've heard our ancestors lived short lives. But I've heard this is bunk because of high infant mortality. Which is it?
AIDS: Can you catch AIDS from a mosquito bite?
Alcohol: does alcohol kill brain cells?
Baths  What State has a law in practice right now requiring at least one bath per year?
Charley horse: Why are those pains in your legs called "Charley Horses"?
Cell phones:  How can cell phones damage your brain?
Cold hospitals:  Why are hospitals cold?
Colds:   I know that viruses spread colds but can getting cold or wet somehow make a person more vulnerable to the cold virus?
Dry-ice burns: Why does one feel a burning sensation when holding dry ice in his hand?
EKG: If "EKG" stands for electrocardiogram, why isn't it spelled "ECG"?
Exercise:  Do heartbeats lessen life?
Flu:  Is there such a thing as the 24-hour flu?
Flu:  Assuming one can pick up the flu from money, how long does the virus stay infectious on paper currency? Is it safe after it's been in my wallet for a few hours?
Hydrogen peroxide:  How does hydrogen peroxide "know" germs when it comes into contact with them? Peroxide doesn't fizz if you pour it on uncut skin, so it's apparently not reacting to simple dirt or oils. But, it fizzes up a storm if it contacts germs, such as in an infected cut.
Life spans:  Why do larger animals live longer than smaller ones?
Life spans revisited:  I read with interest your response as to "why larger animals live longer than small animals (slower metabolism and having a limited number of breaths and heartbeats). But we are all encouraged to exercise in order to live longer. Exercise uses up the breaths and heartbeats faster than someone at rest.  So, what's the deal?
Marijuana:  Does marijuana kill brain cells?
Paper cuts: why do paper cuts hurt more than deeper cuts?
Poison ivy:  why does poison ivy itch and how did it evolve?
Primitive cues, pheromones: why do women and girls living together for extended periods have synchronized menstruation?
SARS:  How effective are surgical masks in protecting against SARS?
Sneezing:  Why do you close your eyes when sneezing?
Smallpox: since a terrorist attack is possible and smallpox a prime candidate, are those of us who had smallpox immunizations as children still immune?
Smallpox revisited:  same question, updated answer---good news!
Swallowing: What happens to food that goes down the wrong way when we swallow?
Water intoxication How much water is too much for a woman of average size?
 

Humans--- intelligence (behavior, customs, emotions, language)

Baby animals:  Why do young animals look cute to us humans?
Biggest city:  What is the largest city on the planet?
Bilingual: What language do bilingual people think in?
Bio clock: I can wake up at a desired time (plus or minus 15 minutes). Over the years I have become proficient. My friends declaim my ability and attribute my skill to other causes. Can you explain this ability please?
Bio clock: How does the bio clock work?
Brain:  What is the weight of the human mind?
Brain:  How many brain cells are in the human brain?
Brain:  How long does it take for the brain to produce new brain cells?
Cousins:  Please tell me what people mean when they say, "That's my second cousin, twice-removed."
Dreams:  What is a dream?
Dreams:  Why do dreams sometimes seem real? For example, if I fall in a dream, it can wake me.
Evil gene: I read that a Swedish scientist may have discovered the 'Evil' gene that causes Man to kill, murder, start wars etc.  Is this 'discovery' another one of those theories classed as nonsense?
Evolution:  How old is man?
Flags:  I heard over the Internet that the American flag flies over Parliament Building on the Canadian $2 bill. Is that true?
Flat Earthers: Which person or group is given credit thinking that Earth is flat?
Illusions:  Recently in the early West Texas morning the moon was setting through a dusty horizon. Why did the moon seem so incredibly large? I am guessing it is the same reason the sun can look so large.
Illusions:   I just read your answer to why rotating wheels appear to go backwards in movies. It’s because the camera snaps different frames 24 times each second, right? But I notice this in real life. Does the eye take a certain number of snaps every second too??
Intelligence, species: How can one species measure the intelligence of another? Are trees smarter than humans?
Language:  Who started the English language?
Language:  How did the English language develop?
Language:  Who invented the word "tree" or "sky?"
Language:  Who is given credit for naming our planet, Earth, our star, the Sun and our natural satellite, the Moon?
Language:  How do tone-deaf Chinese communicate in their tonal language?
Liars:  Can an average person develop the skill to reliably detect liars?
Knights:  I wonder if there were female knights. I mean, not just wearing the title, but also wearing armor and fighting from horseback?
Memory:  How does memory work? Part 1: info flow
Memory:  How does memory work? Part 2:  networks
Memory:  How does memory work? Part 3:  molecules
Memory:  How can I improve my memory?
Memory:  What age group has the best memory?
Navigation:  When men first sought to reach the north and south poles, with the instruments they had at the time — a sextant, a compass and knowledge of the sun and stars — how did they know when they had reached the poles?
Rubbing noses: Do Eskimos really rub noses?
Running:  What’s the average speed of a tiger? What’s the average speed of a human? How fast do humans swim?
She-brain / he-brain:  Do men and women have the same number of brain cells? I wonder because men tend to be larger than women and have larger heads.
Snoring:  Why do people only snore when they are asleep? You breathe all the time, but it's noisier when you are fast asleep.  Why?
Sounds: are some sounds and speech accents grating to all people?
Swimming:  What’s the average speed of a tiger? What’s the average speed of a human? How fast do humans swim?
Synesthesia:  — a person hears a sound and "sees" the "sound color" also. What happens? How does the color appear? Over his whole view range? As an illusion? Does it blot out the rest of his view?
Tears:  Where does a tear come from? How is it formed? Also, what triggers a tear? Is it the emotions, the soul, or spirit? Is it limited to humans?
Thinking:  How do we think? It’s not like we really hear ourselves — its just there, like when we read or write. And how do we see pictures in our mind?
Tickling: what causes tickling? Why can't we tickle ourselves?
Weeping: Why do people weep? Do people in all cultures weep?
Weeping 2: Do other primates weep? Do other animals weep?
Words: What does the 'stan' in Afghanistan, Pakistan, Hindustan... mean?
Words: Do the Eskimo really have 400 words for snow?
Words:  In Ernest Lawrence Thayer's poem, Casey at the Bat, two players are referred to as a "hoodoo" and a "cake". Can you tell me what those terms mean and where they come from?
Yawning: why is yawning contagious?
 

Humans--- senses

Ears: wriggle what muscles do you use to wiggle your ears?
Ears: rumbling If I put my fingers in my ears, I hear a low rumbling sound. What causes that sound?
Eye: speed What is the speed of human sight?
Eye: speed:  I heard at 100 mph what seems to be in front of you is actually behind you because of how fast your eyes receives images. Is this true, and if so how? What speed can your eyes keep up with?
Eye: rubbing When I rub in the corner next to my nose, I see something white moving in the opposite corner of my eye. What is that?
Eye: baby animals:  Why do young animals look cute to us humans?
Eye: color  Does eye color affect vision?
Eye: color  Why are blue eyes blue? 
Eye: color  I know that all white babies are born with blue eyes.  Are ALL babies born with blue eyes, even those of different races?
Eye: color  My mother has green eyes, my father blue.  How did I get light brown?
Eye: color  When and why does a newborn's eye color change?
Eye: color  What causes a person to have one brown and one green eye?
Eye: color  Is it possible for eye color to change as we age?
Eye: color  Can two blue-eyed parents produce a child with dark brown eyes?
Eye color  What color offspring can two blue-eyed parents produce?
Eye: color  If both parents have brown eyes, can they have a child with blue eyes?
Eye: color  My eyes change colors from blue to green to gray depending on what I’m wearing. What causes that?
Eye: color  My eyes change color, constantly: from green to gray to orange to brown, changing even when I’m upset. It must have a genetic explanation but what is it?
Eye: color:  Why are there so many different colors for eyes?  How did the trait evolve?
Eye: color  What exactly are hazel eyes, and what color are they?
Eye color  What caused the natural selection for eye color?
Eye: vision  How does a legally blind person know when to get off the bus?
Eye: vision Why does faulty vision seem to be such a widespread affliction?
Eye & color:  What is the color of a red flower when it is exposed to blue light?
Eye, Primary colors: Why are red, green, and blue the primary colors?
Eye, Primary colors: I thought red, yellow, and blue were the primary colors. Am I wrong?
Eye, Primary colors:  What color are humans most sensitive to---green, red, and blue?
Eye:  Why are we always able to sense it when someone is looking at us? 
Skin temperature: Since our body temperature is around 99 degrees, why do we feel hot when the weather hits the 90s? Since our bodies are hotter than that, it would make sense that any temperature below 99 would feel cool, not hot.
Smell: How do we smell a flower?
Smell: Why does it smell so nice those first few minutes just when it starts to rain?
Smell: Why does rain stop smelling so good as it rains longer?
Smell:   Compared with animals, how good a sense of smell do people have? Is there any difference between men and women?
Synesthesia:  — a person hears a sound and "sees" the "sound color" also. What happens? How does the color appear? Over his whole view range? As an illusion? Does it blot out the rest of his view?
Temperature, black robes: Which is cooler wear in the hot desert: black or white robes?