Q:Hello. Since you're the only science tumblr I follow I thought I would ask you this question. If an interracial couple were to marry, and have children, and their interracial children had interracial children, and so on, how many generations would it take before either the maternal or paternal ethnicity would be completely eliminated? (i.e. if it was a black and white couple and their mixed child married an asian, and their mixed child married an hispanic, and so on.)
Hi there! Thanks for your question. Unforch, this question isn’t really answerable.
Ethnicity and race are social constructs, not useful genetic traits that we can (or should) use to differentiate people. Ethnicity and race can’t “dilute” out (in a genetic sense), because you can’t point to a genome and say “that’s the Hispanic gene” or “There’s the sequence that makes you Asian.” Yeah, we can point to genes that influence skin color or facial features, but that’s not race. It’s biology.
That doesn’t mean that we can’t track genetic differences based on geography and its associated populations, though. We can, and we do. For instance, if we compared the genome sequences of indigenous North, Central and South American populations to, say, Asian and European genome sequences, we would see that the original Americans are more closely related to Asian populations. This matches up to geological studies that suggest that there once existed a Siberian land bridge, and allows us to make hypotheses about human migration patterns across the Earth (not all of those migrations have been voluntary, mind you).
We can, and have, done the same analysis by comparing modern and ancient samples from place X with modern and ancient African DNA, which is how we know that we the first members of our species left Eastern Africa about 70,000 years ago to settle the four corners of the Earth (which has no actual corners, of course).
However, like quick-drying cement, this analysis gets really hard, really fast (insert your own dirtier joke there if you like). Genetic fingerprints get jumbled thanks to the huge amount of genetic crossover that happens as part of our meotic sexytime, and because humans have interbred … a lot. Not in a gross (and genetically dangerous) “banjo player in Deliverance” way, but in a “we’re all related” way. We only have to go back 2,000-4,000 years before we find a person who is a common ancestor for every single human alive on Earth, and, for Europeans at least, anyone who was alive and had children 1,000 years ago is the ancestor of every person of European descent alive today.
So it only takes a few dozen generations before analysis of our crossed-over, interbred nuclear genomes gets so messy that we’re tracing complex statistics instead of neat and tidy family trees. So to make it easier, instead of nuclear genomes, we often compare the tiny, circular genomes that persist within our mitochondria.
You’ll recall from biology class (you were paying attention, right?!) that our mitochondria used to be free-living bacteria, complete with circular, prokaryotic genomes. While most of that ancient genome has disappeared (or migrated to our own nuclear genome), our cellular energy factories still hold a circle of DNA that gets passed down to baby mitochondria when a cell divides and when a mommy and daddy lie down (or stand up, or whatever page of the Kama Sutra they’re on) and do Grown Up Stuff™. What’s weird is that (probably because eggs are big and sperm are small) every one of your mitochondria came from your mom, not your dad.
By comparing mitochondrial genomes from the past with mitochondrial genomes from around the world today, we are fairly certain that one single female of the Homo sapiens crew, living in Africa about 100,000-200,000 years ago, is the ancestor of every living human being today. We call her Mitochondrial Eve. She wasn’t the only human female alive then, and she wasn’t the only human with mitochondria. She’s just the one whose kids ended up covering the Earth.
Yeah, people whose recent ancestors come from South Asia look different from people whose recent ancestors come from Sweden. But that’s just human genetic variation, the same way that I have blonde hair and my friends Jamie and Eric are orange-haired gingers.
People have grouped together (and often excluded other groups) throughout history for a variety of reasons, some of them good, and many of them unthinkably horrible. Because of this, our ancestors often bred with those close to them in geography as well as culture, reinforcing bits of human genetic variation in traits like skin color and facial features. We invented “race”. Evolution just made different kinds of people.
All of this is a long way of saying that while your original question doesn’t have an answer, studying genetic differences based on geography and culture is still important to science. Not because it shows us how we are different, but because it highlights our human connections, and reminds us of our shared experience and common origin in a world that could always use a bit more of that kind of thinking.
Eat Your Tardigrades or You Don’t Get Dessert!
You know this little guy, right? It’s the mighty tardigrade, as featured in the new Cosmos. Tardigrades, also known as water bears, also known as FREAKIN’ MOSS PIGLETS, are microscopic eight-legged animals that can withstand temperatures from near absolute zero to boiling water, absorb extreme doses of radiation, go without food or water for ten years, and even survive the vacuum of space. They can even be completely dried out and ride on the wind to a new home, where they rehydrate and go about their tardibusiness. Tardigrade rain, folks.
In other words, they are BAMFs (bad-ass microfauna).
Oh, and you’ve probably eaten them. Thanks to Meg Lowman, I found out that these water-dwelling super-critters live not only on wild mosses and wet plants, but on grocery store produce like lettuce and spinach. Do you think that a mere rinse or shake under the faucet (or even cooking) is enough to dislodge a radiation-eating space pig? Ha! Not by a long shot, according to Lowman.
So yeah… trying to go strictly vegetarian? You’ve almost certainly eaten some tardigrades. Sorry. Don’t worry, though. They’re totally harmless. I like to imagine that when I eat them, I absorb their power, and become a little bit mightier.
New motto: For strength, eat your vegetables and eat your tardigrades.
Meg Lowman has more about your local tardigrade friends. Also check out Lowman’s awesome research project that helps wheelchair-bound students climb to the top of the forest canopy where they help study tardigrade biodiversity. Science is for everyone!
Hung out with some new fishy friends this morning: Meet Tiktaalik and Neil Shubin! I’m holding my 375 million-year-old great-great-(etc.)-fish-grandfather.
This is what almost four billion years of human evolution looks like when it’s condensed down to ten seconds, thanks to the fine folks behind the original Cosmos.
From self-replicating bags of chemistry to billions of bacteria to crude multicellular blobs to tiny swimming monsters to clumsily creeping fish to fuzzy proto-mammals to weird, naked, two-legged apes … every cosmic blink holds a beautiful story.
If you’d like to retrace your steps along the path of time that ends with you, I recommend this awesome Wikipedia page.
I Ran A Marathon… For Science
This week’s It’s Okay To Be Smart was five months in the making, folks. It was a labor of love, full of blood, sweat, pain and joy. I ran a marathon, for science.
I’ve enjoyed running for as long as I can remember. I’m weird like that. Whether it was on the soccer field or on the road, I just love the peace and pleasure that comes with moving my legs.
But even then, I never understood how human beings were physically able to run a marathon. “26.2 miles?! HA!" I used to think.
I figured the best way to find out was to just do it! This video tells the story.
In the process, I learned how evolution molded our bodies into running machines, how our ancestors first stood up and took off on the hunt, how we fuel our long-distance endurance engines with amazingly efficient cellular ATP factories, what it means to “hit the wall”, and how freaking amazing the Achilles tendon is (perhaps nature’s finest kinetic/potential energy conversion device).
But by far, the most important thing I learned is that our bodies are capable of amazing feats, and just like the evolutionary journey that got us here, you’ve gotta go through a little pain and adaptation to get where you’re going. Luckily I had thousands of you pushing me up every hill!
Hope you enjoy this one, it was a special video to make.
Consider subscribing to It’s Okay To Be Smart on YouTube so you don’t miss an episode!
Just a reminder that a cell is not a bag of water, but rather a crowded metropolis of macromolecules. The reality of cell biology, while more complicated than what your textbook shows you, is much cooler than a simple cartoon.
When you look at the inside of a cell as the crowded, semi-organized, collision-riddled mess that it really is, you’ll look at every bit of biological chemistry in a new way.
(The image of a super-crowded cytoplasm comes from this PLOS paper)
daniel stoupin, a doctoral candidate in marine biology at the university of queensland, has photographed a variety of coral species using full spectrum light to reveal fluorescent pigments that would otherwise be invisible to the naked eye. each piece (click pic for name) is from the great barrier reef. given the complexity of the techniques used, which involve time-lapse and stereoscopic and focus stacked photography, the images take up to ten hours to produce in the lab.
Wow. I thought these were computer-generated protein models or something at first, but these are brilliantly fluorescing corals!!
What might be seeing these stunning fluorescent displays? Coral aren’t known to have any photo-sensitivity (at least past the larval stage), so the obvious candidates are fish, whose eyes would be sensitive to the emitted fluorescent wavelengths.
Do fish like that exist? Earlier this year, researchers at the American Museum of Natural History were photographing their own corals’ fluorescence when they accidentally noticed one of their eels was fluorescing too. No one had noticed because the fluorescence is usually masked in the presence of broad visible light as seen by us land-lubbers.
It turns out that fluorescence in fish is surprisingly common. Water filters out long and medium wavelength light (reds and yellows) as it gets deeper, which is why it’s blue. To compensate for this limited spectral availability, fish have turned to fluorescence as a way to expand the wavelengths of communication and camouflage in their normally azure-monochrome world.
If you feel like reading a beautiful story about cooperation and teamwork, and how it can enrich your life you never thought possible, sit down and read Ed Yong’s The Unique Merger That Made You (and Ewe, and Yew) at Nautilus. Wonderful stuff.
Oh yeah, did I mention it’s about mitochondria and where they came from?
Merry Darwin Day everyone!
“Darwin Took Steps” by Glendon Mellow http://glendonmellow.com
Happy 205th birthday to Charles Darwin! Did you know that much of his work on natural selection was inspired by geology? That’s why it’s important to open your mind to as many branches of science as possible. You never know where inspiration will strike.
You can read the story behind the painting at Glendon’s blog, it’s fascinating to see a piece of art like this go from start to finish.
Why are there 5 steps on the staircase? They represent Darwin’s evolutionary foundations:
- Natural selection
Awesome painting, Glendon!