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Most features in an airplane cabin are designed for a very specific purpose. However, due to the cabin’s complex design, the flight attendants don’t usually take the time to explain every detail to their passengers. (They're more concerned with making sure everyone is safe and comfortable.) However, if you're a curious person who likes to know how things work, we've got you covered. Here are six things you never knew about airplane cabins.

Cabin Lighting Has a Purpose

Have you noticed that the cabin lights dim during takeoff and landing? It turns out that there are two very good reasons for this. According to Reader's Digest, the first reason is safety. If the lights stayed on and were to suddenly switch from bright to dark in an emergency, it would take precious seconds for passengers' eyes to adjust. With dim lighting during takeoff and landing, our eyes are already adjusted — making it easier to find an exit.

The second reason is the mood. Dim lights are more relaxing than bright lights and might calm a passenger who struggles with flight anxiety. Some airlines such as Virgin Atlantic take this a step further by adding colored lights. Virgin Atlantic uses different shades of their brand color for various situations, like a rosy pink color for boarding and a hot magenta color for drinks.

The Temperature Is Cold for a Reason

Passengers often complain about the cold temperature in airplane cabins. Flight staff will provide passengers with a blanket, but they don't ever increase the heat. That's because the temperature on an aircraft has been set in a very intentional way — and it's for your safety.

A study by ATSM International found that people were more likely to faint on an aircraft than on the ground due to a condition called hypoxia. The pressurized environment of an airplane cabin can prevent our body from getting enough oxygen, which causes fainting. The warmer the temperature onboard the aircraft, the more likely this is to happen. To prevent passengers from passing out, airlines intentionally lower the cabin temperature. While this might be slightly uncomfortable, it's much safer for your body.

The Air Is Cleaner Than You Think

A common myth about air travel is that you're sharing air — along with germs and food particles — with all the other passengers on board. Gross, right? In reality, airlines do a great job of maintaining clean air quality onboard the aircraft. They actually use a HEPA (High Efficiency Particulate Air) filter system. According to the International Air Transportation Association (IATA), this is the same type of filter used to clean the air in hospital operating rooms. The next time you fly, don’t worry: Cabin air is cleaner than you think.

Bathrooms Can Be Unlocked From the Outside

While there is a lock inside cabin bathrooms for passengers to use, flight attendants also have the ability to quickly unlock the door from the outside as well. According to Aerotime Hub, this is for passenger safety. In the event of an emergency, flight attendants need to be able to access the bathroom without picking the lock or taking the door off its hinges. This is necessary if a passenger has a health scare or needs assistance while in the bathroom. It can also be used for children who are unable to unlock the door themselves. Don't worry, though: A flight attendant would never just open the door for no reason. They respect passenger privacy and would only use the unlock option in an emergency.

Window Blinds Must Remain Open

During takeoff and landing, most flight attendants will ask that passengers lift their window blinds. Like so many other things on an airplane, there's a real reason for this. Open blinds allow the flight staff to see any issues on the ground or on the airplane itself. Passengers might also report unusual circumstances they observe from their windows. Lifting the blinds also allows our eyes to adjust to the conditions outside quickly in case of an emergency.

Cabin windows also sometimes have triangle stickers on them to mark certain seats. According to Captain Joe, these stickers indicate which windows provide the best view of the wings. Flight attendants can easily look for the triangle when they need to see the wings for safety reasons. According to Captain Joe, these aisles are also great for passengers prone to motion sickness due to the extra stability provided by the wings.

There's a Secret Handrail

Walking down the aisle of a moving airplane can be a wobbly experience — especially when there's turbulence. Most passengers end up grabbing the seats as they walk, which can disturb the people in those seats, but there's actually a better way.

If you watch the flight attendants, you'll notice that they repeatedly reach up to the ceiling when they walk down the aisle. That's because there's a built-in handle rail along the bottom edge of the storage compartment, which can be used to steady yourself. Next time, copy the flight attendants, avoid aggravating fellow passengers, and use this secret rail instead!

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Plastic is everywhere. Look around and you’re bound to immediately notice something made from the stuff. It houses the milk in our grocery carts, makes up the components in our phones, and is woven into the fibers of our clothes. Here are nine facts you might not know about one of the most common materials we interact with every day.

The Very First Plastic Was a Flop

Plastic may seem like a manufacturing miracle limited to the 20th century, but its earliest version actually cropped up around the mid-1800s. English chemist and inventor Alexander Parkes created the first known plastic, eponymously named Parkesine, in 1855, and exhibited it in London in 1862. Parkes’ moldable material was formed from cellulose (aka plant fibers), and it wasn’t cheap. It was also brittle and prone to cracking — two reasons that kept Parkesine from gaining widespread popularity.

Some Early Plastics Were Flammable

By the late 1860s, American inventor John Wesley Hyatt had created celluloid, the first plastic product that would be used for everyday products. Hyatt initially marketed celluloid as a substitute for natural materials, suggesting it was an environmentally friendly swap for the ivory used in billiard balls and tortoiseshell harvested for jewelry and combs. However, celluloid did have a major drawback: It could catch on fire. Billiard balls made from the substance reportedly ran the risk of spontaneously bursting into flame, and cinema film made from celluloid was known to be extremely flammable.

A Plastic Invented in 1909 Is Still Used Today

Belgian chemist Leo Baekeland had already made his fortune from inventing specialty photo paper when he began experimenting with polymers, aka the molecules that make up plastics. Baekeland created a new version of plastic, called Bakelite, in 1907; historians consider it the first fully synthetic plastic made with no naturally occurring materials. Bakelite’s popularity skyrocketed, and the heat-resistant plastic was used for everything from irons, kitchen cookware handles, and telephones to smaller items like buttons and chess pieces. You can still find Bakelite used for electrical components today thanks to its superior insulating properties.

The Word “Plastic” Is Ancient

Modern consumers began using the term “plastic” as far back as 1909, to refer to Bakelite, though the word is actually centuries old. “Plastic” has roots in Latin — from plasticus, meaning something like “fit for molding” or “moldable” — and before that the Greek plastikos, which had a similar meaning.

World War II Fueled the Plastics Industry

Plastics slowly made their way into everyday products during the early part of the 20th century, though World War II had a profound impact on the industry and caused a surge in production. Lower-quality plastics replaced rationed and hard-to-find materials for consumer products, and higher-end versions were used in the war effort. Acrylic and plexiglass made their way inside bombers and fighter planes in place of glass, and nylon was created as a synthetic silk for parachutes, body armor, and ropes. Plastic technology improved during wartime and led to a boom after, with shoppers buying tons of plastic products that were marketed as durable and easy to clean.

There Are Seven Common Types of Plastic

Technically, there are hundreds of types of plastic, though most of the kinds we interact with on a daily basis fit into seven categories. Polyethylene terephthalate (PET, or #1) plastics are most common, found in water bottles, food containers, and polyester. Milk and laundry detergent jugs come from high-density polyethylene (HDPE, or #2). Squeezable bottles, shopping bags, and garbage bags are made from low-density polyethylene (LDPE, or #4). Polypropylene (PP, or #5) is often used for straws and takeout containers. Plastic types #3 (PVC, or polyvinyl chloride) and #6 (PS, or polystyrene) are considered more difficult to recycle, and #7 is a catch-all category for combination plastics, like electronics, DVDs, and clear plastic forks.

Some Plastics Shouldn’t Be Microwaved

Is it safe to reheat your lunch if it’s stored in a plastic container? It depends on the type of plastic used. Heating some plastics can cause the materials to release additives, aka chemicals that help them stay durable and flexible (BPA and phthalates are the most common causes of concern). Polypropylene (aka plastic #5) is generally considered the safest to microwave because it’s heat-resistant, though plastics #3, #6, and #7 should never be heated. Researchers recommend checking to see if a container is labeled as microwave-safe, and steering clear of plastics that are damaged or unlabeled.

Most Plastic Is Never Recycled

Nearly all plastic can be melted down and turned into something new, though most never is. Less than 10% of all plastic products ever created have been recycled, with most ending up burned, in the ocean, or in landfills. That’s because collecting, sorting, and the actual recycling is expensive, far outweighing the cost of producing new plastic items. And plastic manufacturers say that the used containers can only be recycled once or twice before the materials degrade in quality, meaning creating new containers is more reliable — though obviously not great for the environment.

Plastic Shopping Bags Were Created to Save Trees

Swedish engineer Sten Gustaf Thulin created the plastic shopping bag in 1965. At the time, Thulin’s intention was to reduce the number of trees harvested to make paper bags; the plastic version he invented was sturdier and could be used over and over again. The bags, which were cheap to produce, became so popular that they nearly replaced paper bags by the end of the 1980s. Yet there were unintended consequences. In 2002, Bangladesh became the first country to ban plastic bags, a movement that’s now grown to more than 100 countries in an effort to safeguard the seas and reduce landfill waste.

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The world runs on deoxyribonucleic acid, or DNA. Apart from being an excellent spelling bee word, DNA also provides the genetic instructions for the growth, function, and reproduction of all living organisms and viruses. Two polynucleotide chains coil around one another and form the double helix DNA structure that makes you, you. Despite it being the microscopic engine that makes life on Earth possible, humans have only known about the existence of DNA for about 150 years. In that time, scientists have discovered a lot about these genetic building blocks — so much so that doctors can now use gene therapy to treat cancer, while biologists ponder whether to bring back entire extinct species, such as the woolly mammoth. These six facts explore the incredible science of DNA: its discovery, its function, and its impact on human history.

Human DNA Contains 3 Billion Base Pairs

Base pairs form the rung on the twisted DNA ladder, in which each “rung” is composed of nucleotides containing nitrogen bases adenine (A), thymine (T), guanine (G), and cytosine (C). Because adenine always pairs with thymine, and guanine to cytosine, DNA chains are often expressed as just a series of letters (e.g., “AGGTCCAATG” is an expression of 10 base pairs). Human DNA contains 3 billion of these base pairs stretched across 23 pairs of chromosomes, each with different instructions.

Of the total 46 chromosomes, we receive half from our mother and half from our father. The nucleus of every somatic cell (i.e., not sperm or eggs) in the human body contains these chromosomes, but certain cells only access the relevant chromosome for its particular function (eye color, for example, is restricted to a certain section of chromosome 15). DNA usually codes for a protein or group of proteins, which form cells that then become living tissue coalescing together into organs that, when put together, wind up as you.

Humans Share 98.8% of Their Genome With Chimpanzees

Sit a human next to another great ape, such as a chimpanzee or bonobo, and the differences are pretty stark — but our DNA suggests otherwise. The closest living genetic cousin to Homo sapiens, chimpanzees and bonobos each share about 98.8% of our DNA sequence. The similarity comes from the fact that humans shared a common ancestor with these primate species around 9.3 million to 6.5 million years ago, which is basically last week in the context of Earth history. But as humans, chimps, and bonobos evolved separately, the differences slowly grew, with each species adding its own divergent DNA. Although a 1.2% difference doesn’t seem like a lot, small changes in DNA can have major consequences. After all, with 3 billion base pairs, that means that there are still 35 million differences between humans and chimps. It’s also worth noting that even if we share genes with chimps, those genes can express differently, with some turned up high in humans, while the same gene can be a low hum in a chimp or bonobo. All of these differences combined is what separates humans from their primate cousins — and all other living things for that matter. In fact, humans share around 60% of their genes with bananas, and that’s something any self-respecting primate can get behind.

In the 19th Century, DNA Was Called “Nuclein”

Although our current understanding of DNA really started to take off with the description of the double helix structure in 1953, scientists had already known about the existence of DNA for nearly a century by that time. Swiss chemist Johann Friedrich Miescher discovered DNA in 1869, although to arrive at that discovery he had to undergo some less-than-savory science. At the time, Miescher was studying white blood cells, which fight infections and diseases. Although notoriously tricky to extract from a human’s lymph nodes, white blood cells could be found in abundance on used bandages. So Miescher traveled to local health clinics, took their used bandages, and wiped off the pus and grime. He then bathed the cells in warm alcohol to reduce the lipids and also used enzymes to eat through the proteins. What was left behind was some kind of gray matter that Miescher (successfully) identified as a previously unknown biological substance, which he called “nuclein.” In the early 1880s, German physician Albrecht Kossel discovered the substance’s acidic properties as well as the aforementioned nitrogen bases, and by the end of the decade, nuclein was renamed to the more accurate “nucleic acid.”

The Discovery of DNA’s Double Helix Is Controversial

On May 6, 1952, British chemist Rosalind Franklin oversaw the taking of the first photograph depicting DNA’s double helix structure, at King’s College London. Technically her 51st X-ray diffraction pattern, the image became known as simply “Photo 51.” Yet the 1962 Nobel Prize for the discovery of the molecular structure of DNA only honored her colleague Maurice Wilkins, along with English physicist Francis Crick and American biologist James Watson. So what gives?

In 1953, Crick and Watson had written a paper revealing DNA’s twisting shape to the entire world, and only in the paper’s final paragraph mentioned that the discovery was “stimulated by a knowledge of the general nature of the unpublished experimental results and ideas” of two scientists at King’s College. In Watson’s own autobiography, he mentions that Franklin had no idea that her results had been shared with Crick and Watson via her colleague Wilkins, and when she published her own paper later, the reception wasn’t nearly as earth-shattering.

Recent studies have suggested that Franklin was a true collaborator with Watson and Crick, despite receiving much less credit than her male colleagues. Dying at age 37 in 1958 from ovarian cancer (likely due to her work with X-rays), Franklin was ineligible for the 1962 Nobel Prize. (By custom, the award was not handed out posthumously at the time, a rule that became codified in 1974.) Thankfully, history has slowly brought Franklin’s contributions to light and, in 2019, the European Space Agency even announced that their newest Mars rover would be officially renamed the “Rosalind Franklin” — a pretty stellar constellation prize.

All Humans Have Some Trace of Neanderthal DNA

DNA contains all the information that makes up all living things, but it also reveals interesting facts about our past. For one thing, all humans share 99.9% of the same genes, with the 0.1% caused by substitutions, deletions, and insertions in the genome (an important tool for understanding diseases). We also know, thanks to DNA, that humans are much less genetically diverse than other animal species. This means that all 8 billion humans today grew from a population of only 10,000 breeding pairs of Homo sapiens, and that our ancestors likely experienced genetic bottlenecks that caused serious population declines.

Amazingly, glimpses into our human lineage are also locked away in our DNA, because every human on the planet has some genetic material adopted from a completely different species of human — Neanderthals. Although Homo sapiens are the only human species on the planet today, the Earth has played host to upwards of 20 different human species throughout millions of years. For a time, Homo sapiens shared the planet with Neanderthals (Homo neanderthalensis) and even interbred with them. Remnants of those dalliances still live within our chromosomes, passed on from generation to generation. Although Europeans and Asians share the largest percentage of Neanderthal DNA (around 2%), Africans also share a small percentage (which wasn’t discovered until 2020).

Scientists Didn’t Finish Sequencing the Complete Human Genome Until 2022

In October 1990, the Human Genome Project formed to accomplish one goal: to sequence the entire human genome. Regarded as “one of the most ambitious and important scientific endeavors in human history,” the project essentially mapped a blueprint of human biology that greatly improved medicine and sequencing technology. It took 13 years to map the human genome (there are 3 billion base pairs after all), but the project finally declared success in 2003: ”We have before us the instruction set that carries each of us from the one-cell egg through adulthood to the grave,” said leading genome sequencer Robert Waterston at the time.

However, the announcement technically jumped the gun, because the Human Genome Project had only sequenced what was technologically possible, which came out to about 92% of the genome. The last 8% proved to be much trickier, because these regions contained highly repetitive DNA. Over the next two decades, advancements in DNA sequencing methods and computational tools allowed scientists to close the gap, and on April 1, 2022, the Telomere-to-Telomere consortium announced that all 3 billion base pairs had finally been sequenced.