  The famous series of Fibonacci numbers is defined by a recursive equation
saying that each number is the sum of its two predecessors, with the initial
condition that the first two numbers are equal to unity. Here, we show that the
numbers of fatty acids (straight-chain aliphatic monocarboxylic acids) with n
carbon atoms is exactly given by the Fibonacci numbers. Thus, by investing one
more carbon atom into extending a fatty acid, an organism can increase the
variability of the fatty acids approximately by the factor of the Golden
section, 1.618. As the Fibonacci series grows asymptotically exponentially, our
results are in line with combinatorial complexity found generally in biology.
We also outline potential extensions of the calculations to modified (e.g.,
hydroxylated) fatty acids. The presented enumeration method may be of interest
for lipidomics, combinatorial chemistry, synthetic biology and the theory of
evolution (including prebiotic evolution).
