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Anthropometry
Anthropometry is the study of the measurements of different parts of the human body. Common measurements include height, weight, organ size (brain, stomach, penis, vagina), and other bodily metrics such as waist-hip ratio. Each measurement can vary significantly between populations; for instance, the average height of males of European descent is 178cm ± 7cm and of females of European descent is 165cm ± 7cm. Meanwhile, average height of Nilotic males in Dinka is 181.3 cm.

Applications of anthropometry include ergonomics, biometrics, and forensics. Knowing the distribution of body measurements enable designers to build better tools for workers. Anthropometry is also used when designing safety equipment such as seat belts. In biometrics, measurements of fingerprints and iris patterns can be used for secure identification purposes. As for forensics, patterns in anthropometry can be used to identify ancestry or race.

Genetic Drift
Genetic drift is one method by which variability occurs in populations. Unlike natural selection, genetic drift occurs when alleles decrease randomly over time and not as a result of selection bias. Over a long history, this can cause significant shifts in the underlying genetic distribution of a population. We can model genetic drift with the Wright-Fisher model. In a population of N with 2N genes, there are two alleles with frequencies p and q. If the previous generation had an allele with frequency p, then the probability that the next generation has k of that allele is:

$${2N \choose k} p^k q^{2N-k} $$

Over time, one allele will be fixed when the frequency of that allele reaches 1 and the frequency of the other allele reaches 0. The probability that any allele is fixed is proportional to the frequency of that allele. For two alleles with frequencies p and q, the probability that p will be fixed is p. The expected number of generations for an allele with frequency p to be fixed is:

$$ \bar{T}_\text{fixed} = \frac{-4N_e(1-p) \ln (1-p)}{p} $$

Where Ne is the effective population size.

Single-nucleotide polymorphism
Single-nucleotide polymorphism or SNPs are variations of a single nucleotide. SNPs can occur in coding or non-coding regions of genes and on average occur once every 300 nucleotides. SNPs in coding regions can cause synonymous, missense, and nonsense mutations. SNPs have shown to be correlated with drug responses and risk of diseases such as sickle-cell anemia, Alzheimer's disease, cystic fibrosis, and more.