Do humans really share half their genes with bananas?

The popular line that humans share 50 percent of their DNA with bananas is wrong as stated. A looser version, that about half of human genes have a recognizable counterpart in bananas, has some basis, though the figure depends heavily on how similarity is measured and no published study appears to give exactly 50 percent. Shared DNA sequence is far lower, on the order of 1 percent or less. The only relatives who share about 50 percent of your DNA are your parents and children. [1] [2]

Snopes traces the earliest version it could find to a 2001 PBS Nova episode on the Human Genome Project, in which MIT scientist Eric Lander discussed sharing genes, not DNA. A skeptics forum post reaches the same earliest source and could not substantiate the figure. A separate 2013 project led by NIH geneticist Lawrence Brody, originally made for a Smithsonian exhibit, compared predicted banana and human gene products in more than 4 million comparisons. It found about 7,000 hits, roughly 60 percent of genes in one species having a recognizable match in the other, and a video from it cited 41 percent similarity. [2] [3] [4]

Those matches were not identical. Brody said the average similarity between matched proteins was about 40 percent. [4]

Genes, the stretches of DNA that code for proteins, make up only about 2 percent of human DNA, and about 8 percent is gene regulatory regions that switch genes on and off. So sharing half of our genes with bananas translates to roughly 1 percent of our DNA, according to Lewis Thomson of the University of Cambridge and Mike Francis, a bioinformatician quoted by IFLScience. Computational biologist Natasha Glover, working from whole-genome comparisons with zebrafish, which are far closer to humans than bananas are, argued that identical shared DNA would be well below 1 percent. [1] [4] [2]

The figure changes with the definition. A broad definition counts genes that perform the same function; a narrow one counts identical DNA sequences. Mark Peplow of the Science Media Centre made this point in 2003, noting that the chimp figure of 98 percent likewise comes from a specific kind of comparison. Glover tried to be as generous as possible to the 50 percent claim by counting orthologs, genes descended from a common ancestral gene, using the Orthologous Matrix database. The most she found was about 25 percent of human genes orthologous to banana. The NIH-based project reported about 60 percent matching genes by a different, similarity-threshold method. Snopes rated the claim false because no definition gave 50 percent and the claim refers to DNA sequence. [2] [4]

Animals and plants share a common ancestor, a single-celled organism that probably lived about 1.6 billion years ago. Genes for fundamental cell processes, such as making energy and repairing damage, were inherited by both lineages and kept. Brody noted that many things humans and bananas do the same way, like consuming oxygen, rest on genes fundamental to life. Shared genes do not make a person partly banana; what differs most is likely how genes are turned on and off. [1] [4] [5]