Do tall people have more cells?

Do tall people have more cells?

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Within a single species, how does the relative number of cells in the body relate to the relative size of the organism?

Let's say we take two humans, one of them is 6 feet tall and the other one is 5 feet tall. They have similar BMI, age, physical condition, genetic background (aside from height) and are the same sex.

Does the tall one have more cells? Or does he have bigger cells?

PS: Ideally, answers should be backed up by appropriate sources.

PPS: While I'm grateful to everyone for the very nice answers I got, I should point out that I'm waiting for an answer which includes references to accept it.

This is really the most fundamental concept of Cell Biology, so good question. If you look at the size of a any cell from a whale and compare it to the size of any of cells from a mouse, they are in fact quite similar, despite the extreme difference in the overall size of the organisms they are from. There is a reason why cells are small, and it has to do with the fact that they survive based on their ability to absorb enough nutrients from their environment. As a cell gets larger it needs more to survive (because it has a bigger mass). A bigger cell has also has a larger surface area around it (so it can absorb more nutrients).

HOWEVER, there gets to be a point where the mass of the cell is too large for the surface area to compensate for. Mathematically this is shown by what is called the "surface-area-to-volume ratio". Basically, it states that as a a sphere gets larger, the volume increases at a higher RATE than the surface area. So there is a reason cells get only so big, the 60's horror movie The Blob was not scientifically accurate, a single-cell that large (the blob) would not have enough surface area to absorb enough nutrients to sustain itself. Taller (or bigger) people have more cells (not bigger ones) than others.

Effects of osmotic pressure can alter cell size slightly.

When you are talking about taller individuals, you are (I think) really meaning larger people, people with a higher mass. And yes, they have more cells.

Another topic of Cell Biology you may want to explore is apoptosis. Let's say you have two individuals both 180 lbs. one of them is 5' tall and the other 7'. Both these individuals have the same number of cells, but the taller one has a higher percentage of them in the superior and inferior regions of the body. It is the process of apoptosis that sculps an organisms shape.

Not sure it is proven, but this paper makes use of the assumption: West et al, PNAS 99:2473,

Btw, this paper may be relevant for you as it focuses on the metabolic activity, which is not quite propotional to body mass (power 3/4: it's growing slower)

The taller person has more cells. Most cells can only lengthen up to a certain point. Whilst the neuronal cells will be longer and likely some others, the rest of the cells will just be of larger number.

Scientists Discover Children’s Cells Living in Mothers’ Brains

The link between a mother and child is profound, and new research suggests a physical connection even deeper than anyone thought. The profound psychological and physical bonds shared by the mother and her child begin during gestation when the mother is everything for the developing fetus, supplying warmth and sustenance, while her heartbeat provides a soothing constant rhythm.

The physical connection between mother and fetus is provided by the placenta, an organ, built of cells from both the mother and fetus, which serves as a conduit for the exchange of nutrients, gasses, and wastes. Cells may migrate through the placenta between the mother and the fetus, taking up residence in many organs of the body including the lung, thyroid, muscle, liver, heart, kidney and skin. These may have a broad range of impacts, from tissue repair and cancer prevention to sparking immune disorders.

It is remarkable that it is so common for cells from one individual to integrate into the tissues of another distinct person. We are accustomed to thinking of ourselves as singular autonomous individuals, and these foreign cells seem to belie that notion, and suggest that most people carry remnants of other individuals. As remarkable as this may be, stunning results from a new study show that cells from other individuals are also found in the brain. In this study, male cells were found in the brains of women and had been living there, in some cases, for several decades. What impact they may have had is now only a guess, but this study revealed that these cells were less common in the brains of women who had Alzheimer&rsquos disease, suggesting they may be related to the health of the brain.

We all consider our bodies to be our own unique being, so the notion that we may harbor cells from other people in our bodies seems strange. Even stranger is the thought that, although we certainly consider our actions and decisions as originating in the activity of our own individual brains, cells from other individuals are living and functioning in that complex structure. However, the mixing of cells from genetically distinct individuals is not at all uncommon. This condition is called chimerism after the fire-breathing Chimera from Greek mythology, a creature that was part serpent part lion and part goat. Naturally occurring chimeras are far less ominous though, and include such creatures as the slime mold and corals.

Microchimerism is the persistent presence of a few genetically distinct cells in an organism. This was first noticed in humans many years ago when cells containing the male &ldquoY&rdquo chromosome were found circulating in the blood of women after pregnancy. Since these cells are genetically male, they could not have been the women&rsquos own, but most likely came from their babies during gestation.

In this new study, scientists observed that microchimeric cells are not only found circulating in the blood, they are also embedded in the brain. They examined the brains of deceased women for the presence of cells containing the male &ldquoY&rdquo chromosome. They found such cells in more than 60 percent of the brains and in multiple brain regions. Since Alzheimer&rsquos disease is more common in women who have had multiple pregnancies, they suspected that the number of fetal cells would be greater in women with AD compared to those who had no evidence for neurological disease. The results were precisely the opposite: there were fewer fetal-derived cells in women with Alzheimer&rsquos. The reasons are unclear.

Microchimerism most commonly results from the exchange of cells across the placenta during pregnancy, however there is also evidence that cells may be transferred from mother to infant through nursing. In addition to exchange between mother and fetus, there may be exchange of cells between twins in utero, and there is also the possibility that cells from an older sibling residing in the mother may find their way back across the placenta to a younger sibling during the latter&rsquos gestation. Women may have microchimeric cells both from their mother as well as from their own pregnancies, and there is even evidence for competition between cells from grandmother and infant within the mother.

What it is that fetal microchimeric cells do in the mother&rsquos body is unclear, although there are some intriguing possibilities. For example, fetal microchimeric cells are similar to stem cells in that they are able to become a variety of different tissues and may aid in tissue repair. One research group investigating this possibility followed the activity of fetal microchimeric cells in a mother rat after the maternal heart was injured: they discovered that the fetal cells migrated to the maternal heart and differentiated into heart cells helping to repair the damage. In animal studies, microchimeric cells were found in maternal brains where they became nerve cells, suggesting they might be functionally integrated in the brain. It is possible that the same may be true of such cells in the human brain.

These microchimeric cells may also influence the immune system. A fetal microchimeric cell from a pregnancy is recognized by the mother&rsquos immune system partly as belonging to the mother, since the fetus is genetically half identical to the mother, but partly foreign, due to the father&rsquos genetic contribution. This may &ldquoprime&rdquo the immune system to be alert for cells that are similar to the self, but with some genetic differences. Cancer cells which arise due to genetic mutations are just such cells, and there are studies which suggest that microchimeric cells may stimulate the immune system to stem the growth of tumors. Many more microchimeric cells are found in the blood of healthy women compared to those with breast cancer, for example, suggesting that microchimeric cells can somehow prevent tumor formation. In other circumstances, the immune system turns against the self, causing significant damage. Microchimerism is more common in patients suffering from Multiple Sclerosis than in their healthy siblings, suggesting chimeric cells may have a detrimental role in this disease, perhaps by setting off an autoimmune attack.

This is a burgeoning new field of inquiry with tremendous potential for novel findings as well as for practical applications. But it is also a reminder of our interconnectedness.

Non-Mendelian Inheritance

Polygenic traits are complex and unable to be explained by simple Mendelian inheritance alone. Mendelian inheritance is involved when one particular gene controls for a trait, and the traits are discrete. It is named after Gregor Mendel, an Austrian monk and botanist who studied pea plants in the 19th Century. Many of the traits in Mendel’s pea plants showed either/or phenotypes. For example, they could have white or purple flowers, short or tall, or have wrinkly seeds or smooth. This is because each trait was represented by only one gene which had two alleles: dominant and recessive. If a plant had two dominant alleles, or one dominant and one recessive allele, the flowers were purple, while if it had two recessive alleles, the flowers were white.

Polygenic traits also have dominant and recessive alleles, but so many genes play a role in an organism’s phenotype for these traits that the final result is the sum of many complex interactions. It can be hard or impossible to figure out one gene’s effect on a polygenic trait. Instead of being expressed in a ratio as single-gene traits are, polygenic traits are expressed continuously and usually form a bell curve when charted. For example, human skin color varies on a continuous gradient from light to dark, and it is not quantifiable one’s skin color can only be compared to others for a sense of how light or dark his or her skin tone is. Some people have extremely light or extremely dark skin, but the majority of the world’s people do not, and fall somewhere in the middle.

Memory Cells

If your body fights a virus once, the same virus will probably try to attack again. After all the work it took to get rid of that first infection, it would be a shame to have to do it all over again. An amazing feature of your immune system is that it remembers the infections it has fought. This makes it much easier to fight the same virus or bacteria a second, or third, or fourth time.

A Memory cell never forgets

Toward the end of each battle to stop an infection, some T-cells and B-cells turn into Memory T-cells and Memory B-cells. As you would expect from their names, these cells remember the virus or bacteria they just fought. These cells live in the body for a long time, even after all the viruses from the first infection have been destroyed. They stay in the ready-mode to quickly recognize and attack any returning viruses or bacteria.

Quickly making lots of antibodies can stop an infection in its tracks. The first time your body fights a virus, it can take up to 15 days to make enough antibodies to get rid of it. With the help of Memory B-cells, the second time your body sees that virus, it can do the same in thing 5 days. It also makes 100 times more antibodies than it did the first time. The faster your body makes antibodies, the quicker the virus can be destroyed. With the help of Memory B-cells, you might get rid of it before you even feel sick. This is called gaining immunity.

This graph shows how Memory Cells help you to better fight infections. At day 0, someone catches a virus. At day 10, her B-cells start making antibodies, and by day 15 she’s made enough antibodies to destroy all the viruses. Now, she doesn’t make any more antibodies, so fewer and fewer are left in her body. At day 40, the same virus gets in her body again. Since she has Memory B-cells prepared to fight, she can quickly make 100 times more antibodies than she did during the first infection.

Building Memory Cells without getting sick

If you get an infection, you can build up immunity to that specific virus. Another way to get immunity is to get a vaccine. Vaccines are very weak or dead versions of a virus or bacteria that prepare your Memory Cells to fight that specific virus or bacteria. Since vaccines help you gain immunity without getting sick, they are especially good protection for very dangerous illnesses.

Vaccinations in history

The first successful vaccine was against smallpox in 1796. Smallpox is caused by a very contagious and deadly virus. Back then, smallpox was especially scary because people knew so little about viruses, bacteria, or how the immune system works.

It was Dr. Edward Jenner who noticed that young women who milked cows usually caught cowpox, but rarely caught smallpox. He thought maybe getting cowpox prevented getting smallpox.

To test his idea, Dr. Jenner tried infecting people with cowpox on purpose, and then exposed them to smallpox. Amazingly, they didn’t catch smallpox. He didn’t know exactly how it worked, but we now know that cowpox and smallpox have antigens with similar shapes. This means that Memory Cells to fight cowpox can also fight smallpox. Because vacca means cow in Latin, Dr. Jenner called this type of disease prevention vaccination.

After Dr. Jenner’s discovery, it became common to vaccinate everyone against smallpox. It has been so successful that since 1979 there have been no smallpox infections.

Today, we have many vaccines to protect us from getting sick. Most of these are shots, but some scientists are working on vaccines made in plants that you can eat. This might mean one day you won’t get a vaccine shot, you’ll just enjoy a vaccine smoothie!

Symptoms Symptoms

  • Small, firm testicles
  • Delayed or incomplete puberty with lack of secondary sexual characteristics resulting in sparse facial, body, or sexual hair a high-pitched voice and body fat distribution resulting in a rounder, lower half of the body, with more fat deposited in the hips, buttocks and thigh instead of around the chest and abdomen
  • Breast growth ( gynecomastia )
  • Reduced facial and body hair
  • Tall stature
  • Abnormal body proportions (long legs, short trunk, shoulder equal to hip size)
  • Learning disability
  • Speech delay
  • Crypthochirdism
  • Opening (meatus) of the urethra (the tube that carries urine and sperm through the penis to the outside) on the underside of the penis (hypospadias) instead of the tip of the head of the penis
  • Social, psychologic and behavioral problems
  • Intellectual disability
  • Distinctive facial features
  • Skeletal abnormalities
  • Poor coordination
  • Severe speech difficulties
  • Behavioral problems
  • Heart defects
  • Teeth problems.

Which Genes Make You Taller? A Whole Bunch Of Them, It Turns Out

When scientists first read out the human genome 15 years ago, there were high hopes that we'd soon understand how traits like height are inherited. It hasn't been easy. A huge effort to find height-related genes so far only explains a fraction of this trait.

Now scientists say they've made some more headway. And the effort is not just useful for understanding how genes determine height, but how they're involved in driving many other human traits.

At first, these problems didn't seem to be so complicated. The 19 th -century monk Gregor Mendel discovered that traits in his garden peas, like smoothness and color, could be passed predictably from one generation to the next.

But Joel Hirschhorn, a geneticist at Boston Children's Hospital and the Broad Institute, says it became evident that most stories of inheritance were not so simple. Height turns out to be a prime example.

"People's height didn't behave like Mendel's peas," Hirschhorn says. "It wasn't like they you had two tall people and they'd either have a tall [child] or a short [child]. Often the child was partway between the parents."

Scientists explained this 100 years ago, when they realized that height was influenced by many genes, and each makes a small contribution.

Goats and Soda

Americans Are Shrinking, While Chinese And Koreans Sprout Up

So when the human genome was sequenced, scientists like Hirschhorn thought they could plumb that data to track all the height genes, and finally understand how height — and in fact most other human traits — are shaped by our genes.

That effort started slowly. But now, Hirschhorn says. "for height there are about 700 variants known to affect height, each of them usually with a pretty small effect on height, usually like a millimeter or less."

That massive global effort has involved studying the genes of more than 700,000 volunteer subjects. Even so, the traits they've found only explain about a quarter of the inherited height factors.

And, frustratingly, for most of those variants scientists have no idea what they actually do.

Mostly the variants crop up in mysterious bits of DNA between genes on our chromosomes. That makes it hard to figure out their roles.

So Hirschhorn and his army of colleagues, who reported on the effort Wednesday in the journal Nature, tried a new tack.

Their study focused only on variants that are directly in the genes themselves. By knowing that the genes do, they can understand better how variants might influence height. For example, one is in a gene that influences hormones that regulate growth.

The variants within genes are uncommon, but some have a remarkably large influence on height.

"We found some that, if you carry them, you might actually be an inch taller or an inch shorter, as opposed to just a millimeter difference that we found with the previous variants," Hirschhorn says.

Scientists are still very far from identifying all the genes involved with stature, but these new findings do help them better understand the natural biochemistry that influences height.

So far most of our understanding of height has come from scientists who study children who have abnormal growth patterns, according to Constantine Stratakis, a pediatrician and scientific director of the National Institute of Child Health and Human Development.

"There are rare experiments of nature that have told us these genes are involved in the regulation of growth," he says. In fact, he discovered one of those rare genes, linked to a trait called gigantism.

"It leads to babies that double or triple their length in the first year of life," he says.

These natural experiments have been most useful for treating height disorders, but Stratakis hopes that eventually the genome-search methods will provide leads for future treatments.

The bigger lesson here is figuring out how the biology of a complex trait like height really works.

Rare variants can sometimes make a big difference, "but most of the time it's all about systems that interact that define how an organism behaves, or grows, or has a disease, develops a trait and so on," Stratakis says. "And although it's humbling to see the complexity, at this point it's not unexpected."

Global Health

Measuring A Country's Health By Its Height

Hirschhorn and his colleagues are expanding their already massive study of 700,000 subjects. That approach has drawn skepticism from some scientists, who think it's a waste of effort.

David Goldstein, a professor of genetics at Columbia University, says an expanded effort could ultimately implicate every gene in existence, and that hardly helps scientists narrow down the biological factors that contribute to height.

It's likely scientists will never be able to figure out what these hundreds of common variants do to influence height, Goldstein says. Instead, a much better strategy is what Hirschhorn used in this latest study: looking for rare variants that pack a big punch.

"We probably won't get all of the way to explaining 100 percent of the genetic factors, but in some sense that's not really our goal," Hirschhorn says. "Our goal is to use the genetics to do our best at understanding the biology."

To that end, Hirschhorn and his colleagues are not just looking at height they're digging into traits that make people susceptible to diabetes and obesity.

What are the laws of inheritance?

Interestingly enough, genes are passed down from generation to generation in certain patterns, which were first studied by Gregor Johan Mendel. Mendel was originally a priest, but his keen and observant eye drove him to study the characteristics of pea plants. He spent years studying the differences in their height, the color of their flowers, the type of seeds, etc., based on the pairings of their reproduction, and his praiseworthy research earned him the title by which he is now known: the father of modern genetics.

Characters of pea plants studied by Mendel (Photo Credit: Emre Terim/Shutterstock)

Before we deal with the laws of inheritance, let us take a look at alleles: an allele is, in simple terms, an alternative form of a gene. Any gene can have several alleles. For example, a gene for height will have two alleles, short and tall. A gene for color can also have two alleles, such as red and white. Alleles in a certain combination result in a trait!

According to Mendelian genetics, there are three laws of inheritance. The Law of Dominance states that in one gene, one allele is dominant over the other. This &ldquoother&rdquo allele is called a recessive allele. Generally, a pea offspring with one tall allele and one dwarf allele proves to be tall. This means that the tall allele is dominant over the other.

The Law of Segregation states that alleles separate during the formation of the male and female gametes, which means that only one allele for height comes from the father, while the other allele comes from the mother. These alleles combine randomly when the sperm and ovum fuse. Finally, the Law of Independent Assortment states that alleles of one gene do not mix with alleles of another gene. For example, an allele for height won&rsquot mix with an allele for eye color!

Humans Carry More Bacterial Cells than Human Ones

We compulsively wash our hands, spray our countertops and grimace when someone sneezes near us&mdashin fact, we do everything we can to avoid unnecessary encounters with the germ world. But the truth is we are practically walking petri dishes, rife with bacterial colonies from our skin to the deepest recesses of our guts.

All the bacteria living inside you would fill a half-gallon jug there are 10 times more bacterial cells in your body than human cells, according to Carolyn Bohach, a microbiologist at the University of Idaho (U.I.), along with other estimates from scientific studies. (Despite their vast numbers, bacteria don't take up that much space because bacteria are far smaller than human cells.) Although that sounds pretty gross, it's actually a very good thing.

The infestation begins at birth: Babies ingest mouthfuls of bacteria during birthing and pick up plenty more from their mother's skin and milk&mdashduring breast-feeding, the mammary glands become colonized with bacteria. "Our interaction with our mother is the biggest burst of microbes that we get," says Gary Huffnagle, a microbiologist and internist at the University of Michigan at Ann Arbor. And that's just for starters: Throughout our lives, we consume bacteria in our food and water "and who knows where else," Huffnagle says.

Starting in the mouth, nose or other orifices, these microbes travel through the esophagus, stomach and / or intestines&mdashlocations where most of them set up camp. Although there are estimated to be more than 500 species living at any one time in an adult intestine, the majority belong to two phyla, the Firmicutes (which include Streptococcus, Clostridium and Staphylococcus), and the Bacteroidetes (which include Flavobacterium).

For a long time, scientists assumed that these bacteria, despite their numbers, neither did us much harm nor much good. But in the past decade or so, researchers have changed their tune.

For one thing, bacteria produce chemicals that help us harness energy and nutrients from our food, Huffnagle explains. Germ-free rodents have to consume nearly a third more calories than normal rodents to maintain their body weight, and when the same animals were later given a dose of bacteria, their body fat levels spiked, even if they didn't eat any more than they had before.

Intestinal bacteria also appear to keep our immune systems healthy. Several studies suggest that microbes regulate the population and density of intestinal immune cells by aiding in the development of gut-associated lymphoid tissues that mediate a variety of immune functions.

The bacteria also appear to influence the function of immune cells like dendritic cells, T cells and B cells, although scientists don't know the precise mechanisms yet. And one chemical released by the bacterium Bacteroides fragilis is capable of directing how the developing immune system matures.

Further, probiotics&mdashdietary supplements containing potentially beneficial microbes&mdashhave been shown to boost immunity. Not only do gut bacteria "help protect against other disease-causing bacteria that might come from your food and water," Huffnagle says, "they truly represent another arm of the immune system."

Of course, they can't protect against every onslaught, which is why we still have to depend on antibiotics to rid us of some disease-causing infections. But antibiotics don't just kill off the "bad" microbes, they wipe out the "good" ones, too. That's why antibiotic use can cause diarrhea and upset stomach: The drugs interfere with the balance of our bacterial flora, making us sick, Huffnagle explains.

But the bacterial body has made another contribution to our humanity&mdashgenes. Soon after the Human Genome Project published its preliminary results in 2001, a group of scientists announced that a handful of human genes&mdashthe consensus today is around 40&mdashappear to be bacterial in origin.

The question that remains, however, is how exactly they got there. Some scientists argue that the genes must have been transferred to humans from bacteria fairly recently in evolutionary history, because the genes aren't found in our closest animal ancestors. Others argue that they may be ancient relics from evolutionary events that took place early in our species's history and, for reasons unknown, the genes were lost in these ancestors. It's impossible to know for sure at this point.

"There remain to my knowledge no clear cases of human genes recently acquired from bacteria," says Cédric Feschotte, a biologist at the University of Texas at Arlington. "It doesn't mean there are none, but they are not well documented."

Did natural selection make the Dutch the tallest people on the planet?

AMSTERDAM—Insecure about your height? You may want to avoid this tiny country by the North Sea, whose population has gained an impressive 20 centimeters in the past 150 years and is now officially the tallest on the planet. Scientists chalk up most of that increase to rising wealth, a rich diet, and good health care, but a new study suggests something else is going on as well: The Dutch growth spurt may be an example of human evolution in action.

The study, published online today in the Proceedings of the Royal Society B, shows that tall Dutch men on average have more children than their shorter counterparts, and that more of their children survive. That suggests genes that help make people tall are becoming more frequent among the Dutch, says behavioral biologist and lead author Gert Stulp of the London School of Hygiene & Tropical Medicine.

"This study drives home the message that the human population is still subject to natural selection," says Stephen Stearns, an evolutionary biologist at Yale University who wasn't involved in the study. "It strikes at the core of our understanding of human nature, and how malleable it is." It also confirms what Stearns knows from personal experience about the population in the northern Netherlands, where the study took place: "Boy, they are tall."

For many years, the U.S. population was the tallest in the world. In the 18th century, American men were 5 to 8 centimeters taller than those in the Netherlands. Today, Americans are the fattest, but they lost the race for height to northern Europeans—including Danes, Norwegians, Swedes, and Estonians—sometime in the 20th century.

Just how these peoples became so tall isn't clear, however. Genetics has an important effect on body height: Scientists have found at least 180 genes that influence how tall you become. Each one has only a small effect, but together, they may explain up to 80% of the variation in height within a population. Yet environmental factors play a huge role as well. The children of Japanese immigrants to Hawaii, for instance, grew much taller than their parents. Scientists assume that a diet rich in milk and meat played a major role.

The Dutch have become so much taller in such a short period that scientists chalk most of it up to their changing environment. As the Netherlands developed, it became one of the world's largest producers and consumers of cheese and milk. An increasingly egalitarian distribution of wealth and universal access to health care may also have helped.

Still, scientists wonder whether natural selection has played a role as well. For men, being tall is associated with better health, attractiveness to the opposite sex, a better education, and higher income—all of which could lead to more reproductive success, Stulp says.

Yet studies in the United States don't show this. Stulp's own research among Wisconsinites born between 1937 and 1940, for instance, showed that average-sized men had more children than shorter and taller men, and shorter women had more children than those of average height. Taken together, Stulp says, this suggests natural selection in the United States pulls in the opposite direction of environmental factors like diet, making people shorter instead of taller. That may explain why the growth in average American height has leveled off.

Stulp—who says his towering 2-meter frame did not influence his research interest—wondered if the same was true in his native country. To find out, he and his colleagues turned to a database tracking key life data for almost 100,000 people in the country's three northern provinces. The researchers included only people over 45 who were born in the Netherlands to Dutch-born parents. This way, they had a relatively accurate number of total children per subject (most people stop having children after 45) and they also avoided the effects of immigration.

In the remaining sample of 42,616 people, taller men had more children on average, despite the fact that they had their first child at a higher age. The effect was small—an extra 0.24 children at most for taller men—but highly significant. (Taller men also had a smaller chance of remaining childless, and a higher chance of having a partner.) The same effect wasn't seen in women, who had the highest reproductive success when they were of average height. The study suggests this may be because taller women had a smaller chance of finding a mate, while shorter women were at higher risk of losing a child.

Because tall men are likely to pass on the genes that made them tall, the outcome suggests that—in contrast to Americans—the Dutch population is evolving to become taller, Stulp says. "This is not what we've seen in other studies—that's what makes it exciting," says evolutionary biologist Simon Verhulst of the University of Groningen in the Netherlands, who was Stulp's Ph.D. adviser but wasn't involved in the current study. Verhulst points out that the team can't be certain that genes involved in height are actually becoming more frequent, however, as the authors acknowledge.

The study suggests that sexual selection is at work in the Dutch population, Stearns says: Dutch women may prefer taller men because they expect them to have more resources to invest in their children. But there are also other possibilities. It could be that taller men are more resistant to disease, Stearns says, or that they are more likely to divorce and start a second family. "It will be a difficult question to answer.”

Another question is why tall men in Holland are at a reproductive advantage but those in the United States are not. Stulp says he can only speculate. One reason may be that humans often choose a partner who's not much shorter or taller than they are themselves. Because shorter women in the United States have more children, tall men may do worse than those of average height because they're less likely to partner with a short woman.

In the end, Stearns says, the advantage of tall Dutchmen may be only temporary. Often in evolution, natural selection will favor one trend for a number of generations, followed by a stabilization or even a return to the opposite trend. In the United States, selection for height appears to have occurred several centuries ago, leading to taller men, and then it stopped. "Perhaps the Dutch caught up and actually overshot the American men," he says.

How Muscles Grow: Conclusion

For muscle breakdown and growth to occur you must force your muscles to adapt by creating stress that is different than the previous threshold your body has already adapted to. This is can be done by lifting heavier weights, continually changing your exercises so that you can damage more total muscle fibers and pushing your muscles to fatigue while getting a “pump.” After the workout is completed, the most important part begins which is adequate rest and providing ample fuel to your muscles so they can regenerate and grow.

If you want an easy-to-follow program to lose fat and build muscle, check out my 12-Week Body Transformation Program.

Have any questions about how to get muscles to grow? Leave a comment below.