Most mutations involve typos: Something bumps a cell's elbow as it's copying DNA, and the wrong letter appears in a triplet - CAG becomes CCG.
All human beings are, in fact, born with dozens of mutations their parents lacked, and a few of those mutations could well be lethal if we didn't have two copies of every gene, so one can pick up the slack if the other malfunctions.
The idea of critical windows extends beyond just vision, of course: almost every system in the brain has a critical window when it needs to experience certain stimuli, or it won't get wired up properly. The most obvious example is language: if you don't learn a language early on, it's nigh impossible to become truly fluent.
Carbon's eastern neighbor on the table, nitrogen, dresses up diamonds in pinks, yellows, oranges, and brownish tints known romantically as 'champagne.'
Whereas recessive traits require two bad copies of a gene to become noticeable, a dominant trait expresses itself no matter what the other copy does. A benign example of dominance: If you inherit one gene for sticky wet earwax and one gene for dry earwax, the sticky earwax gene wins out every time.
Most people who have encountered mercury have done so after breaking a mercury thermometer. And many of us who saw the liquid balls of mercury scatter across a floor or countertop considered the element the most beautiful on the periodic table.
Everywhere in the universe, the periodic table has the same basic structure. Even if an alien civilization's table weren't plotted out in the castle-with-turrets shape we humans favor, their spiral or pyramidal or whatever-shaped periodic table would naturally pause after 118 elements.
When it comes to the periodic table, the United States really blew its chance to make a name for itself. If you look over a map of all the elements named for cities, states, countries, and continents, it's not surprising that European locales dominate the map.
The body tends to treat elements in the same column of the periodic table as equivalents.
Radium, discovered by Marie and Pierre Curie in 1898, was especially popular: the 'it' element of its day. Radium glows an eerie blue-green in the dark, giving off light for years without any apparent power source. People had never seen anything like it.
The grand saga of how humans spread across the globe will need some amendments and annotations - rendezvous here, elopements there, and the commingling of genes most everywhere.
No element gets people telling crazy stories like mercury does. People have told me tales about pharmacists waxing floors with mercury, mothers rubbing it into babies' skin to kill germs, and 10-year-olds coating dimes in it to make them shine, then blithely carrying them around in their pockets.
Without a functioning hippocampus, names, dates, and other information falls straight through the mind like a sieve.
If stem cells divide equally, so both daughter cells look more or less the same, each one becomes another stem cell. If the split is unequal, neurons form prematurely.
Despite what you might guess, when monitoring your breathing, your body doesn't care whether you're inhaling enough oxygen. It cares only whether you're expelling enough carbon dioxide - that's the gas that sets off the panic button when you're suffocating.
There are a few elements - especially platinum and palladium - that have the amazing ability to absorb up to 900 times their own volume in hydrogen gas. To get a sense of the scale there, that's roughly equivalent to a 250-pound man swallowing something the size of a dozen African bull elephants and not gaining an inch on his waistline.
I didn't mind staying home from school and medicating myself with vanilla ice cream and chocolate sauce. Being sick always gave me another chance to break an old-fashioned mercury thermometer, too.
Except for certain moments - when cells are dividing, for instance - chromosomes don't form compact, countable bodies inside cells. Instead, they unravel and flop about, which makes counting chromosomes a bit like counting strands of ramen in a bowl.
Over the years, humans have managed to incorporate nearly every element, light and weighty, common and obscure, into our daily lives. And given how small atoms are and how many of them there are all around us, it's almost certain that your body has at least brushed against an atom of every single natural element on the periodic table.