the range of genome sizes
Imagine measuring how much 'writing' is stored in different living things by counting the letters of their DNA. You might expect a person to carry far more than a fly, and a fly far more than a flower. Reality is stranger: genome sizes span an astonishing range that mostly does not line up with how complicated the organism seems.
Genome size is usually given as the number of base pairs in one complete copy of an organism's DNA, or as the mass of that DNA (the classic 'C-value', measured in picograms). A small bacterium may hold only a few million base pairs; the human genome holds about 3.2 billion (3.2 x 10^9); some salamanders and lungfishes carry tens of billions; and one fern, Paris japonica, holds roughly 150 billion base pairs, fifty times the human total. Stretched out, human DNA in a single cell is about two metres long, yet it is a tiny fraction of what some amphibians pack into every cell.
This matters because it overturns a tempting assumption — that a bigger genome means a more advanced creature. It does not. Much of the variation comes from non-coding and repetitive DNA, not from extra genes. Genome size influences cell size, division speed, and even how a species copes with its environment, which is why biologists treat it as a real biological trait rather than a curiosity. The puzzle of why the range is so wide and so disconnected from complexity has its own name: the C-value paradox.
A human cell carries about 3.2 billion base pairs, an onion carries roughly 16 billion, and a single fern holds around 150 billion. The onion plainly is not five times 'more complex' than a person — its extra DNA is mostly repeats, not extra genes.
Genome size varies more than a millionfold across life and does not track apparent complexity.
Bigger genome does not mean more genes or more advanced. Most size differences come from non-coding repeats, so genome length is a poor measure of an organism's sophistication.