Merriam-Webster defines chemotaxonomy as the method of biological classification based on similarities and dissimilarity in the structure of certain compounds among the organisms being classified.
Advocates argue that, as proteins are more closely controlled by genes and less subjected to natural selection than the anatomical features, they are more reliable indicators of genetic relationships.
This systematic position of Limulus was controversial for a long time, but has been found to show that human serum is more closely related to arachnids than to crustaceans.
A number of biochemical products like nucleic acids, enzymes, hormones and phosphagens clearly show the relationship of all life forms.
When only fragments of fossils, or some biomarkers remain in a rock or oil deposit, the class of organisms that produced it can often be determined using Fourier transform infrared spectroscopy[1]