 Assuming an informational account of the genome one would expect that the more complex an organism is, the more DNA its genome should contain (this is in fact what many biologists assumed at least until about the 1960s). How to define and assess the complexity of an organism is a tricky issue, but intuitively it seems reasonable to assume that a single-celled amoeba is less complex than an onion, which in turn is less complex than a large metazoan such as a human being, both in terms of the complexity of the workings and the structure of the organism. The expectation was that the DNA content of human cells should be much larger than that of onions or amoebae. As it turns out, however, both the onion and the amoeba have much larger genomes than human beings. The onion, for instance, has a genome of about 16 billion base pairs, meaning it is about five times the size of the human genome (Gregory 2007). The same lack of correlation between genome size and complexity can be found in many other instances (for an overview of different genome sizes see the animal genome size database in the  Other Internet Resources section  below).