In a previous post, I talked about the 4 fields of Anthropology. One of those fields is Physical Anthropology, also known as Biological Anthropology. And one of the things that Physical Anthropology studies is human genetics. So, in this post, I’m going to talk a little about genetics, and then specifically about genetics and height.
Genetics and Heritability
For a long time, people have noticed that babies tend to grow up and look like their parents and other people in their population. For a while, people didn’t know how this happened. Now we know that this is due to a combination of inheriting genes from each parent and environmental factors. But, exactly how much of the trait is due to genetics and how much is due to the environment is different for different traits. So, we are going to look at the concept of heritability, which is how much of the variation in a certain trait is due to genetics.
Some traits are inherited, meaning they are present due to genetics. But other traits are due to environmental factors and don’t have a genetic basis. And, many traits are present due to a combination of both genetics and environmental factors. There is a concept called heritability that describes how much variation in a trait in a population is due to genetics, and how much is due to environment.
Heritability can be expressed as a number between zero and one. If the heritability for a trait is zero, that means that all the variability in that trait in that population is due to environmental factors. For example, your religion is completely due to environmental factors–it is not genetic. So the heritability would be zero.
If the heritability is close to one, then just about all the variability in that trait in that population is due to genetics. An example would be the condition PKU, which stands for phenylketonuria. This condition is inherited in an autosomal recessive pattern.
Many traits are due to a combination of genetic factors and environmental factors, and so the heritability would be somewhere between zero and one. An example is intelligence–your intelligence depends on both genes and the environment.
However, heritability cannot tell us what percentage of a trait is caused by genes and what percentage is caused by the environment. For example, a heritability of 0.8 does not mean that 80% of the trait is caused by genetic factors, and 20% is caused by the environment. Instead, it means that 80% of the variability in the trait in a population is due to genetic differences between people.
Genetics and Height
Now, let’s focus on how heritability works with one trait–height. You can easily tell by looking at people around you that everyone has a different height. But, some groups of people are shorter than others (on average) and some groups of people are taller than others (on average). For example, African pygmies tend to have short stature compared to other groups of people. There is a genetic reason for this. Some genes on chromosome number 3 may explain why these pygmies are short.
Height is strongly affected by genetics. About 70 to 90% of the variability in height in a population is determined by genes. However, this does not mean that 70-90% of your own height is determined by your own genes. It means that 70-90% of the variation in height in a group of people is due to different genes, rather than environmental factors.
Did you know? Scientists have found about 700 different genetic variants that are linked to height!
In some cases, a specific gene causes people to be of short stature. For example, the FGFR3 gene causes achondroplasia. This is a condition where a person is very short, about 4 feet tall, and they have short arms and legs. It is a form of dwarfism and is inherited in an autosomal dominant manner. But, most people with achondroplasia do not inherit the condition from their parents. Instead, they have a de novo genetic mutation, which is when a mutation occurs for the first time, rather than getting it from their parents.
In other cases, a gene can result in people being rather tall. For example, the FBN1 gene causes a condition called Marfan Syndrome. This condition affects the connective tissue in the body, and people with Marfan Syndrome are usually tall. This condition is inherited in an autosomal dominant pattern. However, about 25% of cases are caused by a new mutation, rather than inheriting the condition from your parents.
Want to learn more about genetics and height? Check out this article, “How much of human height is genetic and how much is due to nutrition?” from Scientific American.
Thanks for reading!