Blonde=sexy. Many adult jokes reaffirm you and many men indeed believe in it. But how about brunette? It seems fine to me. What’s the purpose of God to make this kind of difference?

The word—race—is for this purpose. Human beings are classified based on geographic locations and physical appearance such as skin color, hair color, and nose shape. Race is also falsely linked to people’s inner mentality and outer behavior.

So who and how defined “race”?

Johann Friedrich Blumenbach, a student of listmania Carolus Linnaeus who classified all plants and animals human then knew, adopted his teacher’s geographic classification of human beings and developed the racial classification: Caucasian, Ethiopian, Mongolian, American, and Malay, in his 1795 book.

Ironically, Blumenbach, a professor at Gottingen, was never a racist. In fact, to avoid grouping people based on mentality or behavior, he created his classification based on the beauty of physcial appearance and the origin of human beings. He even believed that human beings were from the same group of H. sapiens, although he thought people from mountain Caucasus was the most beautiful and the start of modern human beings.

Nevertheless, Blumenbach’s classification did rank human beings. With just one more step, the hierarchy of human beings was used literally and wrongly. Racism has hurt human beings tremendously.

Most people now accept the idea that human beings, like many other animals, orient physical appearance to adapt to environment. Flat nose is to fast dissipate heat, while long and protrude nose is to warm cold air; slant eyes (epicanthic folds) are due to sand and wind, black skin color is for UV protection, to name just a few.

Any of these characteristics can appear in all racial groups. In other words, each physical appearance is distributed continuously in any human population. However, why most northern European girls are blonde, while Brunette most likely appeared in Asia? It seems to me there is no obvious reason that hair color has anything to do with environment.

As I have mentioned in the previous skin color post, although south-east Asian people have similar amount of UV exposure as those in tropical Africa do, the skin color of those Asian people still look more like yellow than black. However, skin color develops quickly. For example, some Indonesian people have skin color as dark as tropical black African do, but other physical characteristics of these Indonesians are very similar to the rest of south East Asian people. Nobody will question their yellow Asian identity. This suggests that these black Asian people redeveloped dark skin color after they moved to Indonesian islands. Therefore, why didn’t other people who lived in hot places change their skin color? Moreover, why do Italian people still have light skin, despite they have been there for several thousands of years?

One answer to these puzzling questions is sexual selection. People mate with people like themselves. Visible appearance is what we use to judge people. As suggested in my previous post on beauty criteria, average, or majority, sets the standard of beauty (this is the standard used by human beings, but not in peacock in which extreme is considered beauty). If most women in a group have huge butt, men tend to copulate with women having huge butt because they think it beautiful. This indeed occurred in Khoisan people inSouth Africa. Furthermore, if the whole population is made of people with slant eyes, flat nose, straight hair, and shovel-like front teeth, these characteristics will be considered as normal and thus beautiful. These characteristics are more likely preserved in the population. If for whatever reasons this group conquered the land, the whole region will be that type.

There are more examples of physical characteristics which result from sexual selection. Tall, big, and masculine men are more attractive because they look more promising for survival and reproduction (more or less like the peacock way). Blue eye color, has been described as pure and beautiful in English literature. Blond hair has long been attributed to sexy. However, there are some physical characteristics which had neither survival nor sexual advantages. They are probably natural genetic drifting. Examples include fingerprint, color of nibble, birthmark, toenails, and so forth. The dominance of these characteristics may result from bottleneck phenomena.

However, one should keep in mind that modern human beings had many grand-scale migrations, either voluntarily or forced. For example, the movement of old German people other part of Europe led to many Germany like languages, and the migration of Slavic people made east Europe all Slavic descendents. In addition, wars and diseases can easily eliminate a country within handful years. For example, about 1500 year ago, there were a large number of “whites” living in the center of China with “yellows”. Those “whites” even established a big country. However, within a year or two, the new yellow emperor effectively killed all “whites” (also any people looked like “whites”), leaving China as one pure “yellow” country. Another genocide was the disappearance of most of American Indians.

In modern societies, the uniformity is more likely created by these types of population shifting. The environmental force is less important than sexual attractiveness in shaping our physical appearance.

Next post, the link from race to prejudice and stereotype.

If we look around us, we may unintentionally group people simply based on skin color: black, white, yellow, etc. Eighteenth century people also defined race based on these observations. Sadly, we have used this definition until now.

Yes, I know there is less genetic variation between race than within race (to be scientific: 10% between race vs. 90% within race). However, from the sociological perspective, the underline genetic uniformity doesn’t matter. Skin color, facial appearance, body shape, and other physical characteristics are the only criteria people differentiate each other. The prejudice and stereotype against people of color is plain there.

Elaborating tedious genetics and numbers is of no use persuading people to abandon the race idea. Only after people know how human beings have developed different skin colors and other physical characteristics may they throw away stereotypic ideas and treat each other fairly. In this post, I will discuss the evolution of skin color.

The “out of Africa” hypothesis says that we were all from Africa. But were we all black a million years ago, similar to those who are still living there? How could Chinese end up yellow, while European look white and pale? If there were some prehistoric human beings trapped in deep ice, we would be able to answer these questions definitely. Unfortunately, we don’t have that luxury. As in most scientific disciplines, let’s start with some assumptions.

Both our cousins–chimpanzees and apes in Africa– have hairy bodies, and under the hair are light skins. If we feel comfortable to accept the common ancestor idea, we can assume that our ancestors were also covered by much hair and had light skin millions of year ago.

When first human-like animal (H. erectus, man who stands) walked out of jungle, the first thing happened to them must be hair-loosing. Directly exposed to the sun light, extra hair blocked the release of heat. However, without hair, skin got burned under the sun. The ultraviolet (UV) is also harmful to skin cells and causes skin cancer. It is known that melanin, the substance makes our skin dark, can protect cells from UV damage.

Well, things are not so simple. Although skin cancers do pose a threat to unprotected skin, it takes years to develop skin cancers. By the time of having skin cancers, most primitives might already complete his reproduction duty, or be killed by other diseases or during fights. The natural selection force from skin cancers seems not very strong.

Astute researchers noticed the importance of folic acid (folate) in our human body. Folic acid deficiency may cause neural tube birth defects. Folic acid is also an essential component in biochemical reactions in our body. Dark skin may serve as a protecting layer from destroying folic acid by UV.

Furthermore, we all know that exposure to sun light during winter can increase vitamin D in human body, thus preserving calcium for normal bone development. Therefore, people who live in cold places are likely to develop light skin so that enough UV can penetrate skin to initiate vitamin D synthesis, while people with dark skin reached a balance between the detrimental and beneficial effects of strong UV radiation in tropical areas.

So far so good. Modern human beings are descendents of Homo Sapiens (man of knowledge) in Africa, who were descendents of archaic Homo Erectus. H. Sapiens had already been hairless and had black skin for a million years. Nevertheless, those fretting earlier human beings started to move away from the middle of Africa around 150,000 year ago. They could go north which was a large grassland (that Sahara became desert was a recent development). Some kept moving on, crossed the Arabic peninsula, and reached cooler place such as Mesopotamia land. Some might psychotically kept moving on (or were probably defeated in tribe fighting) and reached Europe and south Asia. Because the UV is less in the northern world, some people might have better survival chance due to their mutated genes which could lead to light skin. In other words, skin color was reversed from black to light color.

Now here is the perplexing question: why modern East Asians (including Chinese) have yellow skin color while Europeans have white skin, given not much difference in environment between Asia and Europe? The above theories gave a generally explanation why people have dark or light color. It can’t explain why people have different light skin colors. As matter of fact, south-east Asian people who had similar amount of UV exposure still had lighter skin than those in tropical Africa. The residual between observed and predicted skin color index (based on UV exposure) was much larger among south East Asian people than those among African.

Furthermore, if early human beings move slowly and continuously, skin color should have a continuous spectrum. For example, black people live in the south of Africa do have lighter skin than tropical Africans like Sudanese do. Among American Indians who crossed Bering strait 11,000 year ago, Those who lived in tropical areas did have darker skin than northern American Indians did.

One possibility is the bottleneck phenomena. If for some reasons one subgroup who happened to have very light skin or yellow skin (due to non-random mating within its limited area) successfully conquered other places, the whole area may have light skin, even though some places may not be good for light skin. For example, northern Europeans might conquer the southern Europeans (who might have dark skin), thus creating a uniformly white European population. This type of migration might occur lately, say at the end of Neolithic period, or even later. For instance, the Aryan’s invasion to India practically eliminated all indigenous people (who had dark skin) and made all Indians look like the whites. Because later human beings could protect skin in other ways such as cloths, the evolution force of skin color didn’t matter much any more.

In Asia, it is possible that a group of east Asian people with somewhat yellow skin kept moving north and probably conquered neighbors too. Because yellow skin is just fine in either warm or cold weather (but not for tropical weather), they finally reached the farthest place. Most of them kept hanging around in the land of east Asia, while some crossed Bering Strait and kept marching in American land.

Some people thought that if the migration from Africa to other places started from the beginning of H. erectus, the later comers (e.g. H. Sapiens) might mix with old ones whose evolution was independent from that of Africa (multi-region hypothesis). The recent discovery of Homo floresiensis seemed to support this hypothesis. Nevertheless, most evidence until now suggested that all modern human beings were from the same African tribe.

Skin color is just one indicator of racial difference, the evolution of physical appearance is more complicated. I will discuss it in the next post and also give another explanations on skin color.

The February issue of Journal of the National Cancer Institute featured two articles on coffee consumption and cancer: a Japanese group claimed that drinking caffeinated coffee could prevent half of hepatocellular carcinoma (liver cancer) in the Japanese cohort. Previous studies have shown that drinking coffee could reduce the risk of gallstone and liver cirrhosis. These might inspire the Japanese group to investigate the protective effect of coffee on liver cancer.

On the other hand, Willett from Harvard U reported that drinking coffee was not related to colon rectal cancer in his Nurse and Physician cohorts, contrary to earlier German study which suggested a protective effect of coffee. Nevertheless, Willett did hint that drinking decaffeinated coffee might prevent rectal cancer.

Although the above information is encouraging, it reminds me an old story about coffee drink and pancreatic cancer. A report by Charles Hennkin in 1980s showed an increased risk of pancreatic cancer among those who drank coffee regularly. That study was criticized due to its case control study nature and the neglect of adjusting for confounders. Subsequent studies didn’t reach any consensus.

We should notice that all these controversial results are from observational studies. Although they are widely used in etiological inference, they can’t determine the causal link, a fact many news media grossly ignored. I am not saying results from random controlled trials are better. Ill designed trials are worse than observational studies. Recent scandal on Vioxx is such an example. Nevertheless, observational studies do suffer many weaknesses.

Take the Japanese coffee study as an example. The study only measured coffee consumption once, at baseline, which was many years ago. People do change habits over the time. In addition, the study didn’t have information on hepatic virus infection (in particular HBV), a recognized risk factor for liver cancer. Hepatic virus infection is very high in the East Asian. It is very likely that those who had HBV infection would abstain from coffee. In addition, those who drink coffee were more likely living in a modern lifestyle than those who don’t drink. Studies have shown that immigrants from Japan to the US had reduced risk of liver cancer and stomach cancer than those native Japanese (NiHonSan study). The change of diet is likely the reason, but no one knows which diet factor cause the reduction. Furthermore, liver cancer tends to cluster in areas or in specific population, probably due to the cluster of HBV infection, or genetic susceptibility. Therefore, even with many statistical adjustments in their models, all of their claims are inconclusive. In fact, most these claims will be unvalidated in future studies.

Are there any good stuff in coffee? Not really. There is no mystery why coffee makes you feel high. It is caffeine, the substance many people addict to. The magic antidotes—antioxidants such as flavonoids— are widely available in other fruits. If coffee can help you, many other fruits will help you too.

I don’t drink either coffee or tea. Instead, I live in a primitive way. I achieve the same stimulating effect by flushing myself with two big bottles of plain water a day. It’s much safer than drinking coffee. Anyway, coffee hurts my esophagus and stomach.

In the last post, I have tackled carbohydrates in vegetables and fruits. However, the rationales behind eating whole vegetables and fruits are mainly the benefits of vitamins, minerals, and other nutrients. This post continues the previous discussion by focusing on vitamin supplements.

Vitamin supplement has been a controversial topic for a long time. Almost all people who discovered vitamins won Nobel Prize. 20 years ago, any positive results of vitamin supplements might land on prestigious journals such as New England Journal of Medicine (NEJM). 10 years ago, many negative results also appeared in NEJM. Now, people got so tired of all these confusing messages that a recent meta-analysis of vitamin E was published in an obscure British journal.

On the other hand, almost 40 years after Linus Pauling’s promotion based on his good faith, the US spends $6 billion a year on variety of vitamin supplements. It seems that people just take it no matter what.

The debates on the usefulness of vitamins center on Vitamin A, C, and E, the magical antioxidants. News media make the word “antioxidant” housewife’s vocabulary now. However, unless you have some knowledge of biochemistry and pathophysiology, you probably have no idea why antioxidants are good for you.

Let me give a heuristic explanation. The way our human body uses energy is to burn glucose or fat to generate ATP, the energy currency inside cells. The furnace is mitochondria, a small gadget our cells captured during the evolution. After glucose or fat enter mitochondria, some enzymes break down carbon and hydrogen chains; protons are then used to generate ATP. Remember, protons (positive) and electrons (negative) are pairs. Since we have used up protons for ATP, the extra electrons will generate by-products–reactive oxidative species (ROS) such as free radicals and superoxides. They are very active, ready to oxidize anything they encounter. For example, when ROS meet with low density lipoprotein (LDL, the bad lipoprotein), it can oxidize LDL. The ox-LDL will attract macrophages to clean the mess. The LDL-loaded macrophages become foam cells in the blood vessel layers, thus forming atherosclerosis. Therefore, eliminating ROS or blocking the oxidation will lower the oxidative stress, reducing the risk of heart diseases. Furthermore, since ROS can damage cells or proteins, anything that can stop oxidation may also prevent cancer and delay aging.

From the very beginning of human history, people have frantically searched for magic antidotes to counter diseases and hope to live forever.If the above oxidation theory is true, what else could be better than antioxidants?

Vitamin A, C, E are such antioxidants, readily available in our daily diet. They have also been synthesized as pills to satisfy human needs. A small pill per day will have more than enough antioxidants, together with other vitamins and minerals for your body.

The disturbing fact is that many random-controlled studies suggested that extra vitamin A and E intake had no effects on your health. Even worse, some studies showed that a mega dose intake of beta-carotene might increase the risk of lung cancer among smokers. Recent meta-analysis also suggested that mega-dose of Vitamin E might lead to more deaths. In addition, a high dose of vitamin C will generally be unnecessary because vitamin C is water soluble. Extra vitamin C will simply be flushed away.

Nevertheless, people will not be deterred by these arresting results. The oxidation theory is just too beautiful. Anyway, you only need very little of something to do the fighting. If beta-carotene or vitamin E do not work, something else may work. For example, recent fashion is to take pills with lycopene, which is abundant in tomatoes, or “A to Z” nutrients as Centrium has advertised. I also know some people are conducting feeding studies on flavonoids, which is widely available in fruits and tea.

However, if all antioxidants are widely available in vegetables and fruits, and if the combination of antioxidants in natural foods is probably optimal because human body is geared towards these foods by evolution, and if there are other unknown antioxidants, anti-cancer, or anti-aging stuff in the natural foods, why don’t we just eat sufficient and various vegetables and fruits? We can plainly forget about all those vitamin supplements.

Bible doesn’t tell us what kind foods Adam and Eve consumed in the Eden. The only fruit mentioned is the forbidden apple. However, I think their diet must include a variety of vegetables and fruits because they live in the forest and was supposed to live forever. We should find a way to go back to that forest and live happily ever after.

Let’s go back to the jungle!

We all know there is a war in Iraq right now. But imagining you were teleported back 10,000 years to the land between Euphrates and Tigris rivers, what would you see?I know, people were mostly naked at that time (isn’t it cool?). But please take a peak at their kitchens. You would be surprised that they were eating pretty much the same foods as we are now: barley and wheat in somewhat processed form plus some goat meats. Some people might have a cup of milk in their hands. Chinese, on the other side of Eurasian continent, were busy harvesting rice and millets, or domesticating chicks and pigs. Unfortunately, after so many years of civilization, we are no more innovative in food discovery than those primitive guys were.

It is even worse that we are adopting the primitive dietary style. I was appalled by this idea after I meticulously digested the 2005 Dietary Guideline. For instance, the Guideline suggests that almost all vegetables should be eaten in raw or minimally cooked. Fruits should be eaten without peeling. Should I forget about the exquisite Chinese cuisine? Should I eat like a gorilla, biting fruits without appreciating the delicacy of nature?

Furthermore, whole grain, the big star in this Guideline, is particularly gross. Everybody who is sensitive to the color, smell, and texture of breads will boycott the dark and coarse whole grain breads, let alone those faked whole grain breads covered with flakes of oatmeal. They are tough to my mouth, harsh to my esophagus, and harmful to my stomach. I miss the tasty white breads.

So why did those stupid experts advocate whole grains, or whole foods in general? Let’s again get armed with modern knowledge. We know the main ingredients in grains, vegetables and fruits are carbohydrates plus many vitamins and minerals. Let’s tackle carbohydrates in this post and leave vitamins and minerals to the next post.

Carbohydrates can be broadly grouped into simple carbohydrates and complex carbohydrates (what a dumb classification!). Simple carbohydrates consist of one or two sugar molecules. Glucose, fructose (fruit sugar), and galactose (in milk) are typical single sugars. Lactose (stuff causes diarrhea after drinking milks), sucrose (table sugar) and maltose (sweetness in beer) are common double sugars.

On the other hand, complex carbohydrates consist of long chains of sugar molecules (polysaccharides). They have to be digested and broken down to single/double sugar to be absorbed and fuel our body.

After the invention of water powered mill, refined grains are appreciated by all civilized human beings. The refine process reconstructs the complex carbohydrate structure so that glucose chains are nicely aligned and bound together. The product, starch, can be quickly broken down to single or double sugar and easily absorbed. Unfortunately, most vitamins, minerals, fibers, and other nutrients are likely lost during the process.

We all know that blood glucose level will increase quickly after having a chocolate snack. The same thing occurs after you finish a plate of foods. However, due to the different structure of complex carbohydrates, different foods raise blood glucose level at different speed. White bread and white rice, which mainly consist of glucose in easily digested forms, can raise blood glucose level very fast, even faster than eating a spoon of table sugar (sucrose=glucose+ fructose). Fructose has to be converted to glucose to be useful.

A rapid increase of blood glucose will cause an increased secretion of insulin, a hormone made by pancreatic beta cells. Insulin can reduce blood glucose level by facilitating the usage and storage of glucose. Knowledgeable readers may point out that a malfunction of insulin stuff will cause diabetes, one of the leading risk factors in heart diseases. Diabetes mellitus can also cause blindness and amputation of extremities such as foot.Probably one or two of your relatives already have diabetes.

So it indeed makes some sense to treat carbohydrate seriously. The speed of raising blood glucose by foods is called Glycemic Index (GI). GI is standardized against glucose and scaled at 0-100. The rule of thumb is that you should always look for GI below 50, called low GI foods if you are worrying about your glucose. In general you should avoid eating too much foods with GI greater than 70.Potatoes and watermelon are among high GI foods. There was also a comprehensive table in American Journal of Clinical Nutrion by Australian researchers three years ago.Google it. The concept of GI is getting popular.

But wait. There is another important carbohydrate I didn’t mention. Yes. The fiber. There are two types of fibers: water soluble fiber and insoluble fiber (again a dumb classification). Water soluble fiber includes gum and pectin, and insoluble fiber includes cellulose, hemicellulose and lingnin. Human beings can’t digest fibers (if we can, we will live like cows, constantly munching straws). They most likely increase the bulk of stool instead.

In modern point of view, fibers are more important than many other carbohydrates. Eating a lot of fibers can make your stomach full, thus preventing more energy intake. Sticky fibers such as gum or pectin can delay the digestion of other carbohydrates, retain dietary fat in intestines, reduce cholesterol, stimulate bowl movement, and most of all, prevent colon cancer and heart diseases. Can you imagine other stuff that won’t contribute your energy intake while reduce the risk of death?

Most vegetables and fruits are rich in fibers, but not in refined grains. That is, Chinese white rice is not good for you. If you understand that white rice also has lower percent of protein than other grains, the small body of Chinese can be attributed to white rice. What a bummer!

The take home message is this: be gross, live primitively, man.

PS. Prune juice can relieve constipation because it has lots of soluble fibers. But be prepared, the taste of prune juice may give you a surprise.

The next topic: move your butt, let’s go back to jungle!

“Oh man, what a dumb question. Everybody knows it is for fun.”

Hey, I hear your laughing. Cut it out! My topic is hard science, OK? If you are not comfortable with this topic or anti-evolution, please feel free to entertain yourself with something else in my blog such as diet and physical activity.

A cursory reflection on human sexuality tells us that our human beings live mostly in monogamy (even among most traditional tribes in Africa), and can enjoy sex at almost anytime anywhere (what a great pleasure). In addition, most women are willing to engage in sexual activity even during infertile periods, for example during pregnancy, lactation, or after menopause. The purpose of sex seems more likely for recreation rather than for reproduction.

It is instructive to compare human sexual behaviors with those of our closest relatives—gorillas and chimpanzees whose ancestors were the same as ours about 9 million years ago. In African jungles, gorillas live in small groups in which one male fertilizes several females (called harem), while chimpanzees live in big groups in which both male and female chimpanzees can freely copulate with the opposite sex (called promiscuity).Furthermore, both female gorillas and female chimpanzees accept sex only during ovulation periods. It seems that gorillas and chimpanzees copulate solely for reproduction. Additional analyses in other primates yield a more confusing picture: some live like gorillas while others live like chimpanzees.

There is another not so obvious phenomenon in primate sexuality. Without modern knowledge and techniques, human beings–both men and women– lack the instinct to detect the exact time of woman’s ovulation, while many female primates can show some visible signs to attract males during their ovulation periods, such as swollen or red derrieres.

Critical readers may wonder why I target woman’s ovulation and sexual receptiveness instead of something about man. Well, we must hold the assumption that men are “cheaper” in dispersing their genes at anytime. In fact, almost all male animals tend to philander with other females after discovering their successful fertilization. On the other hand, women invest much more than men do in this gene transmission business. Pregnancy, lactation, and daily caring for her kids consume too much time and energy in women.

Anyway, in human beings, the concealed ovulation and continuous sexual receptiveness in women, together with monogamy must have something to do with kids because it takes many years of growth for a kid to be independent. Mothers are unlikely able to raise children without some aids. Since men are such irresponsible creatures, it falls on women to figure out ways to retain their men. One naive theory postulates that if a woman can offer sex to his man whenever he wants, the man is likely to stay with her to protect kids. However, this sex-for-family theory is overtly superficial because primates like gibbons don’t need continuous sex to maintain monogamy, while others such as chimpanzees and bonobos have more sex than human beings do, but they live in promiscuity.

Furthermore, human species were evolving towards large groups in which all couples have to cooperate to survive. Adultery is always a challenge in large groups (even in modern society, 20% Americans acknowledged this type of sin). The concealed ovulation in women must have some merits in evolution.

Therefore, some theorists started with the concealed ovulation in women to examine human sexuality. One theory (proposed by Alexander and Noonan) suggests that without knowing a woman’s exact ovulating time, a man has to have sex continuously with her until she gets pregnant. He also has to stay home to guard his mate because any intrusion may yield fertilization. On the other hand, if he himself intrudes other couples, his effort is likely wasted because the chance that the other women ovulate at the time of copulation is low, while he left his mate unguarded. Therefore, the best strategy is to stay at home and focus on one woman.This facilitates the development of coparenting which greatly increases the survival of their offspring.

Keen researchers also notice that infanticide is common in animals. A non-biological father may abandon or kill his stepchildren because they don’t bear his genes. For example, imagining a human tribe in which infanticide is a social norm, if a man died of accidents, diseases, or fights, his children would be killed or abandoned by his successors. It is a big waste for both the tribe as a whole and the mother’s heavy investment on the kids. However, if every man may be the kid’s father, the kid is likely to be protected by the whole tribe. To accomplish this, a woman needs to have sex with as many men as possible before pregnancy. Therefore, by hiding her ovulatory signs, she can copulate with many men. Every copulation may lead to fertilization, and thus every involved man may think the kid has his genes. This theory (suggested by Sarah Hardy) explains the concealed ovulation and promiscuity very well. Unfortunately, our human beings live in monogamy.

Is it possible both theories have some elements of truth? We need data to test them.

Let’s take a look at our relatives again. Among 68 high primate species, ten of eleven monogamous species have concealed ovulation and the rest one only exhibits slightly visible ovulatory signs. Does concealed ovulation lead to monogamy? No. Out of thirty-two species with concealed ovulation, twenty-two species don’t live in monogamy but instead in promiscuity or harems. Further cross-sectional analyses suggest that ovulatory visibility may have nothing to do with mating system, and vice versa. Now we stuck.

A better analysis suggested by Sillen-Tullberg and Moller is to construct a family tree for these primates. It turns out that both mating system and ovulatory visibility switched back and forth several times over the evolution process in primates. By timing these switches, we can conclude that concealed ovulation evolved from promiscuity or harems, while monogamy never evolved in species with boldly visible ovulation. It is possible that the pathway to monogamy is from promiscuity/harems to concealed ovulation and then to monogamy.

Inferred from the family tree, the common ancestor of human beings, gorillas, and chimpanzees might have harem mating system and slightly visible ovulation. Because human species were evolving towards big society, women evolved concealed ovulation, thus permitting them to mate with many men to ensure the survival of their babies. This trait might lead to the ability of continuous sexual receptiveness in women. Armed with this weapon, women might then entice and lock strong men to protect their children. Continuously copulating with the strong men also assured them that they were endorsing their own genes. Families were then born. Together with fast intelligence development, monogamy was on the way.

On the other hand, chimpanzees might reinvent the promiscuity with visible ovulatory signs, while gorillas might keep the tradition of our ancestors. It serves them well.

Natural selection has no specific goal except for preserving genes. As the flip-flops of mating system and ovulatory visibility have demonstrated, a trait developed in one situation may be used for other purposes or may be dropped in other situations. Evolution is never a straight line.

Thank you for reading thus far, I hope you appreciate the origin of recreational sex. Needless to say, there is more to learn why sex is fun. Why don’t men nurture babies? Why do women live for a long time after menopause? I recommend the little book “why is sex fun? — the evolution of human sexuality” by Jared Diamond. For a general idea of genes and evolution, the book “the selfish gene” by Richard Dawkins may be of your interest.

During the internship in ophthalmology (stuff dealing with eyes), I was amazed that so many young ladies were willing to cut their eyelids to make “double eyelids”. For most people, the procedure (blepharoplasty) removes a tiny slice of muscle or skin from each upper eyelid or involves just the incision itself. After one week of recovery, voila, those eyes are beautiful, glaring wisdom in addition to alluring sex.

I was born in the southern China where people with single, heavy eyelids were few and considered ugly. It is no wonder that many young ladies are willing to endure the sufferance of the surgery and to take the risk of having skewed eyes. Nevertheless, I was so keen in identifying surgery-made “double eyelids” that when I went to the northern China, I found that about one third of young ladies in campus were blinking those God-forbidden eyelids.

Women, probably due to evolution pressure, are frantic in modifying and remodifying their already gorgeous bodies. Beauty, in the beholder’s eyes, is the only goal of female existence, despite that Emily Dickson claimed there was no definition of beauty.

Surprisingly, before Galton’s facial composition study, people believed that beauty stemmed from the deviance from common people. However, using Galton’s methods, Perett et al. in 1994 neatly demonstrated that beauty actually meant averaging. In his study, students rated higher on those faces averaged over hundreds of faces. It is the symmetry and average that make a woman’s face beautiful. It reminds me Audrey Hepburn whose western body blended with oriental mystery was once so attractive to me. (http://www.audreyhepburn.com/)

On the other hand, some studies showed that an average of beautiful faces was more attractive than the average of common faces. So there is indeed something inside a beauty. A little characteristics do make one more attractive, but not peculiarity, as most societies are not fond of extremes.

What is considered beautiful? In almost all societies, large eyes, small chin, and full lip are attractive. A waist of about 30% of hip, and a big breast are also sexually favorable.

By saying this, we should keep in mind that society, or culture plays a significant role in forming the standard of beauty. Judged from sculptures in Greek and Roman and paintings during the renaissance, a healthy and plump body was considered beautiful in those days, similar to the figures before Song dynasty in China. However, there was difference of beauty standard between western and eastern societies during that period. Most western pictures showed large eyes and full lips, while women in most Chinese pictures had small eyes and lips, which appeared on most Chinese faces.

During Song dynasty (probably even during the end of Tang), something weird happened. Men were favoring slim women, to such an extent that even small feet were considered attractive. The foot binding custom spread from upper class to lower class. The powerless women had to endure tremendous sufferance to bind their feet from the very beginning of their childhoods so that they could marry decent husbands. For God’s sake, it was abandoned 100 years ago.

There were also some weird things happened in Europe during that period. In France, women were hopelessly wrapping their waists so that they looked slim and attractive. In England, as suggested by female writers such as Jane Austin or George Elliot, showing a full blown breast was considered vulgar. Women had to hide their precious gifts. By the way, George Elliot was really an ugly lady (depicted as “hideous”); but her intelligence won her many fans.

Anyway, in modern society, after a blaze of plumpness (e.g., Marilyn Monroe), men are favoring skinny women more than ever. Furthermore, with abundant foods available, fatness is considered unhealthy, lazy, and sexually unattractive. In addition to eye surgeries, breast enlargement, and skin lifting, women (and also men) are enthusiastically engaging in liposuction for the sake of both beauty and health.

Does a beautiful face really matter? Sure, it does. Studies in 1960s already showed that among those randomly-matched students, men were more likely to ask for future dates if their female partners were physically attractive. Although many people claimed that they wouldn’t relate beauty to intelligence, studies repeatedly suggested that people indeed rated a higher intelligence to the beauties than to those with plain bodies. Other lines of research also confirmed that physical attractiveness meant more career opportunities for both men and women. People were even judged as more competent after cosmetic surgeries than before surgeries.

It is interesting that men perceive women’s attractiveness differently from women themselves. Men actually prefer a middle ground (say body mass index(BMI) at 20-25) while women tend to go extremes such as BMI below 20. Unfortunately, men and women don’t talk to each other about setting up beauty standards.

After more than 60 years of promoting feminism, women are still trying to impress men sexually. The power of nature is too strong.

Narcissus, a beautiful but intolerably proud and disdainful young man, fell in love with himself. When seeing his image in the pool, he could not get away but remained fixed until he was turned into a flower of his own name. However, as a flower, narcissus yields no fruit when it’s ripe and simply fades away.

Narcissus is a person who has an extremely high self-esteem—valuing himself too good.

But what is self-esteem? The definition is straightforward: self evaluation of your own worth. How attractive are you? Do you think you are important? How successful is your life? Or, simply answer this daily greeting: How are you?

American society seems to be maniac in boosting self-esteem. Thousands and thousands of books, programs and scientific literatures are convincing people that if you have high self-esteem, you will be a winner, sooner or later. Dr. Baumeister is one of many psychologists who disbelieve this credo.

In a recent Scientific American review, Dr. Baumeister and his colleagues argued that boosting self-esteem is worthless, if not harmful (http://www.sciam.com). To solidify their arguments, the authors discussed school achievement, youth sex, drug use, and family and career success. They showed that a high self-esteem poorly predicted academic success in high school and college students. Self-esteem was also not related to job performance. People with high self-esteem were more prone to prejudice, violence, drug use, unrestrained sex, and more extramarital affairs, simply due to their curiosity and tendency of overlooking others.

So what was wrong with those positive self-esteem studies? The authors pointed out several fundamental flaws in many previous studies. One flaw was self-reported outcomes in many psychological studies, thus subjecting to self serving bias—people always want to show good impression to others. For example, to objectively measure physical attractiveness, studies used independent panels to examine the attractiveness of participants. These studies found that there was no relationship between attractiveness and self-esteem despite that there was a strong relationship between self-reported attractiveness and self-esteem. It seems that people are beautiful in the eyes of themselves. Recall Narcissus.

Another flaw in many positive studies was that they examined the correlation but interpreted the relationship as if it was causal. For example, there was a strong correlation between self-esteem and self-reported happiness. We can’t say that self-esteem causes happiness because the other way around can also be true. It is possible that people are successful in work and feel self-worthy and happier.It may exist a positive feedback: more successes—more self-esteem—happier life—more successes.

So what can we do? It seems to everybody that something must be good when viewing oneself positively. It at least makes you feel good. Unfortunately, the authors didn’t give us definite answers. Studies found that self-esteem might improve one’s persistence when facing failure. Those with higher self-esteem sometimes did perform better than those with low self-esteem. It seems to me these reasons are enough to boost one’s self-esteem.

The real problem of self-esteem, I think, lies in its magnitude. When one boosts his self-esteem to the extent of arrogance and egotism, it is certainly too much and likely causes social problems. Otherwise, keep working on your self-esteem because lower self-esteem is harmful to you in all respects.

“Some days are blue, some days are yellow”, Dr. Seuss versed in My Many Colored Days. We need good feelings to live through tough days, and some good feelings to enjoy good days. That’s the way life goes.

PS. I read the story of Narcissus from the Francis Bacon’s writing. I can’t help telling you that narcissus is also a toxic plant.