Isotope analysis
A recent development in forensic science is the isotopic analysis of hair strands. Hair has a recognisable growth rate of 9-11mm per month or 15 cm per year. Human hair growth is primarily a function of diet, especially drinking water intake. The stable isotopic ratios of drinking water are a function of location, and the geology that the water percolates through. Sr, Sr and oxygen isotope variations are different all over the world. These differences in isotopic ratio are then biologically 'set' in our hair as it grows and it has therefore become possible to identify recent geographic histories by the analysis of hair strands. For example, it could be possible to identify whether a terrorist suspect had recently been to a particular location from hair analysis. This hair analysis is a non-invasive method which is becoming very popular in cases that DNA or other traditional means are bringing no answers.
Long hair
In most current cultures, it is more typical for women to wear long hair than for men to do so. An American study shows significant correlation between hair length and age, which indicates that younger women tend to have longer hair than older women. A significant correlation was also found between women's hair length and hair quality. Moreover, hair quality was correlated with the women's perceived physical health. Consistent with principles of evolutionary psychology, these results indicate that hair length and quality can act as a cue to a woman's youth and health, signifying reproductive potential. The correlation between the woman's hair length and marital status, or number of children, was however not more than to be expected from the correlation between hair length and age.