Gene

Even identical twins with the same genes can differ in handedness: one may be left-handed and the other right-handed. Such discordance in twin studies shows that although genes influence handedness, they do not determine it alone.

About 8% of the human genome is made of ancient retrovirus sequences. When viral DNA entered sperm or egg cells, the infection did not die with one body; it became inheritable, passed down like a gene. Our DNA carries molecular fossils from viruses that infected our ancestors.

Cats cannot properly taste sweetness. A sweet receptor normally works as a pair of proteins, but in cats the TAS1R2 gene is a broken pseudogene, so they cannot make a functional sweet-taste receptor.

Natural redheads may need more anaesthetic. A 2004 study found people with the MC1R gene variant behind red hair needed up to 20% more, as the variant shifts hormones governing pain response. But other studies disagree, so it's too soon to generalise.

98% of Korean people carry a mutation in the ABCC11 gene that makes body smell nearly undetectable, and 99% have dry, flaky earwax. In contrast, 97% of Europeans and Africans have strong body odor and wet earwax. A single gene variant produces both differences simultaneously.

Corn's ancestor is teosinte, a plant resembling foxtail grass with almost nothing edible. Humans spent centuries on selective breeding, picking the best mutations, to create modern corn. Today, a single corn kernel has more nutrition than an entire ear of ancient teosinte.

Between 1–4% of modern human genes came from Neanderthals. These include the SLC16A11 gene linked to obesity and diabetes, as well as hair loss genes. The Khoisan people of southern Africa, who had no contact with Neanderthals, carry almost none of these genes.

Dogs and wolves differ by just 0.04% genetically. Part of this difference includes variations linked to Williams syndrome in humans — a condition causing extreme sociability and no hostility toward strangers. Some scientists suggest dogs may essentially be wolves with Williams syndrome.