**Telephone ring** **Telephone ring** **Telephone ring** Crash Course Biology hotline.

Dr. Sammy, your friendly  neighborhood entomologist speaking.

How may I help you? [Student Sammy] Hi Dr. Sammy, long-time viewer, first-time caller. I’m so stressed out.

I have a test after lunch,  a flute recital tonight,   an essay due tomorrow, my crush  left me on read 3 days ago. And I'm losing my tater tots. Like literally!

Like I don’t even know where they're going... How do I keep it together? [Dr. Sammy] I'm so glad you called.

Would you believe that I'm not most  people's first choice for life advice? I know! I'm a biologist — life is literally my specialty.

And biology is everywhere. We've found it in cancer cells and chemical  reactions, evolution, and elephants. But the science of life is  also in your everyday life.

And believe it or not, there is a bit of  biology at work here in your tater tot tumult. Actually, quite a bit. So yeah, I will answer this question,  and ALL your questions to show you   how your life brings together biological  principles from the tiny to the tremendous.

Prepare to be amazed… as soon  as I find my theme music. We’re gonna have to tie a bell around that thing; I feel like I lose it every week! [THEME MUSIC] Man, I’m gonna miss that theme music. Okay, back to your question.

I know it feels like you don’t have it  together, but rest assured: your body does. Through constant tweaking, your molecular  machinery strives for homeostasis:   a steady state that allows life to  keep living, whatever it’s facing. I mean not whatever you’re facing, if it’s  a flamethrower, you’re probably toast… Your body has been shaped by millions of years of   evolution to respond to any and  all challenges to that stability.

So, that stressed-out, can’t  even-hold-onto-your-tots   feeling is actually a sign that  everything’s working properly as   your body manages stress with a rush  of chemical messengers: hormones. Your brain, sensing a threat, is revving  your body up to do something about it. A surge of hormones triggers your heart to beat  faster and your breath to quicken – pumping   more blood and oxygen through your body to your  vital organs to help you run away from a lion,   or, in your case, think more quickly for a test.

As long as they don’t overdo it making you  too jittery to get those thoughts out clearly. And a stress response is a good thing — as  long as it turns off when it’s not needed. A body stuck in stress mode  is more likely to get sick.

You can help your body turn off stress  mode by getting enough sleep, exercise,   time with supportive friends, and of course,   by remembering to study well in advance of your  exam rather than cramming the night before. For now: breathe. Deep belly breaths interrupt the  stress response and relax your muscles.

Seriously, breathe: you’ve  got this, tots or no tots. [Pajama Sammy] Dr. Samuel. I love cheesy popcorn, but my dog keeps eating it!

And I get her her own popcorn-flavored  treats, but she just keeps eating mine. What am I supposed to do ? [Dr. Sammy] Well, you could send your pup on over to my place.

My jokes are extra cheesy so she can  munch on those to her heart’s content. But, seriously, we’re connected to other   living things — from our food  systems to our energy sources. So thinking ecologically here  might solve your popcorn problem.

You and your dog are two organisms in the same  food web, jostling for the same popcorn niche,   like two anole lizards living in the  same tree, snacking on the same crickets. When two organisms are competing  neither gets as many resources as   it would without competition so  even the winner loses a little. That’s a life lesson right there.

So, how do you prevent that popcorn-poaching? Do as the anoles do! Different anole species manage to live in harmony  by snacking in different parts of the tree.

Canopy for one, trunk for the other. So, split your niche! Your dog is probably going to keep  plundering your popcorn if you leave   it where she can reach it, but if  you put it up on the top shelf,   well, chances are she isn’t going to  get a ladder and go looking for it.

Though if that does happen, could you call a   brotha back because I’m definitely  gonna need to study this behavior. [Spaghetti Sammy] Hey, uh, hey doc, I got a bit of a situation here, a little… spaghetti sauce…on my favorite shirt. And I just don’t know how to get it out. And we’re kinda in a time-sensitive  situation here if you catch my drift. [Dr.

Sammy] That sounds…concerning. Uhhhhh… well, I’m gonna assume this is a  food-based stain, so to get that Ragu rag-gone,   you’re gonna wanna grab one of the  most amazing molecules around: water. It supports life and busts stains through its  power of dissolving some things but not others.

It’s not just a solvent, it’s The Solvent. Now, you’re also gonna call upon  the awesome power of enzymes:   proteins that speed up chemical reactions. Enzymes are in all living things, you included.

They’re part of how the molecules  composing spaghetti that actually   make it into your mouth get  broken up into usable energy. And thanks to biological knowledge, we’re  able to harvest enzymes from microbes grown   in laboratories (like the tiniest livestock  ever) and put their power in detergents! Thanks little guys!

Anyway, here’s what you’re gonna  do: add some water to the stain. Then scrub in some enzymatic detergent,  can’t provide you any brand names;   Crash Course prides itself  on being detergent impartial. But, you’ll want one that has enzymes  specially suited to certain molecules,   like lipases that break apart fats  and amylases that break down starches.

And that’s most of what spaghetti is. Then other detergent molecules with water-loving   heads and water-repelling tails will  lift those bits up and off the fabric. Where the water will dissolve  them and wash them away.

Pasta La Vista, baby. [Rocky’s Mom] Dr. Sammy, I love Rocky. But, he’s just not bringing a lot  of engagement in my life right now.

Should I get maybe a tarantula, a goldfish,  or a coconut crab as my first pet? I just think Rocky really needs a friend. Thank you for taking my call. [Dr.

Sammy] A predator no heavier than a grapefruit, a fish that can live over a decade,   or a top contender for the most  beautiful species on Earth? Not that I'm biased or anything. Because really, all of those options have a lot in   common not only with each  other but also… with you.

Like, you’re all quite literally  made of the same stuff:   biological molecules formed billions of years ago. We living things just sort of pass  this stuff around the food chain,   and despite our different bodies, we use many of  the same chemical reactions to harness energy. On top of that, you and all your  prospective pets have traits that   were passed down by evolutionary  forces that helped you survive.

Like, that’s why both you and your  hypothetical tarantula have hair,   though it evolved independently in each of you. And sadly, unlike the tarantula, you can’t  torpedo your hair at stuff that scares you. Missed opportunity evolution.

But the things we don't have  in common... matter a lot. Unlike you, the goldfish needs water to breathe. And that coconut crab — well, it’s gonna  take up a lot more room than either of them,   which means it’ll need more calories.

It’s not easy maintaining  such dramatic awesomeness. All that said, since this is your first  pet, caller, I’d recommend sticking with   something more low maintenance – like a hissing cockroach or maybe a giant African millipede... Yeah...

Yeah.. [Cool Sammy] Aye yooooo Dr. Sammy you answered, Good look bruh. Aye uuuh for real for real, I’ve got no  idea what I want to be when I grow up.

I know I love fashion. But like biology is cool, too. You feel me?

Like, what should I do bruh? [Dr. Sammy] What to do with a life? You've provided a question that  the science of life can’t answer.

But, biology will be in the answer no matter what. Take your interest in fashion, for starters. Cotton fabrics have been around for at least 5,000 years because humans selectively  bred wild plants for extra fluff.

Some clothes are even made with red pigment  called cochineal produced by insects. And fashion and biology  are still meeting up today! Like, there are these copper-infused textiles  that kill off, fungi, viruses, and other microbes.

Who knows, maybe you’ll design the  world’s an antimicrobial swimsuit. And biological knowledge could take you  down a bunch of other fascinating paths. You could develop new medicines,  cosmetics, or compostable plastics.

You could train athletes, treat diseases, or breed  crops that resist pests and tolerate droughts. You could write about biology for the public,   teach it in a high school, or  be a naturalist at a state park. You could be a civil engineer, picking plants for cities to support native  wildlife and connect fragmented ecosystems.

Or maybe you’d enjoy being a research scientist,   asking super-specific questions about whale  songs, liver cells…or honey bees, like me. [High School Sammy] So, I’m going to college next year, and I  want to be a whole new me when I get there. How do I have, like, a personal evolution? Would a new hat help? [Dr.

Sammy] Oh caller. Caller, caller, caller. A new hat is always a gamble.

I barely made it out of my last bucket hat era. But anyway, caller, I’ll start with the bad news. As an individual organism, you can’t evolve.

Not biologically, anyway. Evolution only happens in  populations over many generations,   as some individuals pass on  their genes and others don’t. So there are limits here.

You can try a new hairstyle. But you can’t evolve longer  leg bones or X-ray vision. That doesn’t mean you can’t change, though.

What it seems you’re thinking of  is a metamorphosis and that kind   of change can happen to a creature during its  lifetime like with tadpoles or caterpillars. We use the term a bit more  loosely with humans though. In fact, you’re changing right now.

Many of your cells—trillions of tiny lives inside   you that together are you—are  constantly getting replaced. How’s that for a Ship of Theseus problem? On top of that, you’ve inherited a particular mix of genes that, for the most part, can’t change.

But their expression as actual traits can. Expression is shaped by your ongoing experiences,  which can change you — throughout your lifetime. So you can’t evolve biologically  speaking, but you’re always changing.

You’re still part of evolution’s long story. And I find some comfort in that. We’re all here because our ancestors made it.

And you know what? A new hat is always a risk. But if your ancestors could  make it through everything   it took for you to be here, why not go for it.

And might I recommend a fedora? It’s a great conversation starter. Whether you just joined today or you’ve  been with us for all fifty episodes,   there’s one idea we want to  leave you with: connection.

All the layers of life we’ve talked  about — cells, genes, anatomy,   ecology — are constantly interacting,  shaping the world that you experience. They link you not only to all of  life…but to the universe itself. Nearly every element in your body traces  back to explosions from long-ago stars,   scattered and looped into cycles  far older than our species’ memory.

You’re made of borrowed  stardust, just passing through. But you ignite this cosmic arrangement  with a life that’s entirely yours. Wherever life takes you, the science  of life will be there—helping   us understand ourselves and the big, boisterous,  four billion-year-old family we’re all a part of.

So from me, Patty, and all 8,351 members  of the Yeasty family…thanks for watching. This series was produced in  collaboration with HHMI BioInteractive. If you’re an educator, visit  BioInteractive.org/CrashCourse for   classroom resources and professional development  related to the topics covered in this course.

Thanks for watching this episode of Crash  Course Biology, which was filmed at our   studio in Indianapolis, Indiana, and was  made with the help of all these nice people. If you want to help keep Crash  Course free for everyone,   forever, you can join our community on Patreon.