Browsing Tag: TED-Ed

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    Can you solve the fish riddle? – Steve Wyborney

    October 15, 2019


    You are the cargo director on the maiden
    voyage of the S.S. Buoyant, and you’ve agreed to transport
    several tanks containing the last specimens of a critically
    endangered fish species to their new aquarium. Unfortunately, as you’re passing
    through shark-infested waters, the boat is battered by a fierce storm,
    throwing your precious cargo overboard. And to make matters worse, no one seems certain
    just how many fish tanks are missing. Fortunately, you have a rescue sub
    at your disposal, but only enough fuel for one trip
    to the ocean floor. You need to know where the tanks are so you can gather them all
    in one quick pass. Not a single fish can be lost. You decide to scan the three sectors
    of the ocean floor where the cargo could have landed. Thermal imaging shows 50 organisms
    in the area, and you quickly realize that that number
    includes both your fish and some ravenous sharks. You flip on the sonar
    to get a better look. The image for Sector Alpha shows
    four tanks and two sharks, the image for Sector Beta shows
    two tanks and four sharks, and the image for Sector Gamma
    is blank. Your sonar has malfunctioned, and you’re going to have to go
    with the info you have. You check the shipping notes, but all you learn is that each tank
    had the same number of fish inside. The cargo hold had space for anywhere
    from 1 to 13 total tanks. And finally, the old captain tells you
    that this area has the odd property that no two sectors can have the same
    number of sharks, but every sector will have at least one, and no more than seven. There’s no time to waste. The tanks won’t withstand the pressure
    much longer. As you descend in the sub,
    you review everything you know. How many fish tanks do you need
    to find in Sector Gamma? Hurry, the fate of an entire species
    depends on you. Pause here if you want
    to figure it out for yourself. Answer in: 3 Answer in: 2 Answer in: 1 At first, it seems like there are just
    too many missing pieces of information. After all, you don’t know how many fish
    or how many tanks there are, let alone how many fish are in each one. But then you remember the best way to compare multiple pieces
    of partial information – a table. Since we know there are thirteen
    tanks at most, and we already see six tanks
    in Sectors Alpha and Beta, we know the total number of tanks
    must be between 6 and 13. We also know that each sector has
    a different amount of sharks with no more than seven in each one. Since there are two in Sector Alpha
    and four in Sector Beta, Sector Gamma can have
    1, 3, 5, 6, or 7 sharks. What about the number of endangered fish? Out of the 50 total organisms
    in all three sectors, we know at least seven are sharks, leaving a maximum of 43 fish
    inside all the tanks. And the more sharks we find in Sector 3,
    the fewer fish there are to save. Now, remember that the fish are
    equally distributed across all the tanks. Why is that important? Because it means that one of the possible
    values for the total amount of fish must be divisible by one of the possible
    values for the total amount of tanks. And looking at the table, we can see
    that the only combination that works is 39 fish divided between 13 tanks
    with three fish in each. With sharks swarming around, you quickly pilot the sub through
    the first two sectors before retrieving the remaining
    seven tanks in Sector Gamma. You’ve saved the species
    and taken an impromptu dive. All in all, not a bad day,
    unless you happen to be a hungry shark.

    The secret lives of baby fish – Amy McDermott
    Articles, Blog

    The secret lives of baby fish – Amy McDermott

    October 9, 2019


    What you’re looking at
    isn’t some weird x-ray. It’s actually a baby yellow tang surgeonfish
    at two months old. And you thought your childhood
    was awkward. But here is the same fish as an adult, a beautiful inhabitant of the
    Indian and Pacific Oceans’ coral reefs and one of the most popular captive fish
    for salt water aquariums. Of the 27,000 known fish species,
    over a quarter live on coral reefs that make up less than 1%
    of the Earth’s surface. But prior to settling down in this
    diverse tropical environment, baby coral reef fish face the difficult
    process of growing up on their own, undergoing drastic changes,
    and the journey of a lifetime before they find that reef to call home. The life cycle for most of these fish begins when their parents spew
    sperm and eggs into the water column. This can happen daily, seasonally,
    or yearly depending on the species, generally following lunar or
    seasonal tidal patterns. Left to their fate, the fertilized eggs
    drift with the currents, and millions of baby larvae
    hatch into the world. When they first emerge,
    the larvae are tiny and vulnerable. Some don’t even have gills yet
    and must absorb oxygen directly from the water
    through their tissue-thin skin. They may float in the water column
    anywhere from minutes to months, sometimes drifting thousands of miles
    across vast oceans, far from the reefs where they were born. Along the way, they must
    successfully avoid predators, obtain food, and ride the right currents
    to find their way to a suitable adult habitat, which might as well be a needle
    in vast haystack of ocean. So, how did they accomplish this feat? Until recently, marine biologists thought of
    larval fish as largely passive drifters, dispersed by ocean currents
    to distant locales. But in the last 20 years,
    new research has suggested that larvae may not be
    as helpless as they seem, and are capable of taking
    their fate in their own fins to maximize their chances of survival. The larvae of many species are
    unexpectedly strong swimmers, and can move vertically in the water column
    to place themselves in different water masses and preferentially ride certain currents. These fish may be choosing the best routes
    to their eventual homes. When searching for these homes, evidence suggests that larvae navigate
    via a complex suite of sensory systems, detecting both sound and smell. Odor, in particular, allows larvae to
    distinguish between different environments, even adjacent reefs, helping guide them toward their
    preferred adult habitats. Many will head for far-flung locales
    miles away from their birth place. But some will use smell
    and other sensory cues to navigate back to the reefs
    where they were born, even if they remain in the
    larval stage for months. So, what happens when larvae
    do find a suitable coral reef? Do they risk it all in one jump
    from the water column, hoping to land in exactly
    the right spot to settle down and metamorphose into adults? Not exactly. Instead, larvae appear to have
    more of a bungee system. Larvae will drop down in the water column
    to check out a reef below. If conditions aren’t right,
    they can jump back up into higher water masses and ride on, chancing that the next reef
    they find will be a better fit. But this is the point
    where our knowledge ends. We don’t know the geographic movements
    of individual larva for most species. Nor do we know which exact environmental
    cues and behaviors they use to navigate to the reefs
    they will call home. But we do know that these tiny trekkers are more than the fragile
    and helpless creatures science once believed them to be. The secret lives of baby fish
    remain largely mysterious to us, unknown adventures waiting to be told.

    Can you solve the river crossing riddle? – Lisa Winer
    Articles, Blog

    Can you solve the river crossing riddle? – Lisa Winer

    September 18, 2019


    As a wildfire rages through
    the grasslands, three lions and three wildebeest
    flee for their lives. To escape the inferno, they must cross over to the left bank
    of a crocodile-infested river. Fortunately, there happens
    to be a raft nearby. It can carry up to two animals at a time, and needs as least one lion
    or wildebeest on board to row it across the river. There’s just one problem. If the lions ever outnumber the
    wildebeest on either side of the river, even for a moment, their instincts will kick in,
    and the results won’t be pretty. That includes the animals in the boat
    when it’s on a given side of the river. What’s the fastest way for all six animals
    to get across without the lions stopping for dinner? Pause here if you want
    to figure it out for yourself. Answer in: 3 Answer in: 2 Answer in: 1 If you feel stuck on a problem like this, try listing all the decisions you can make
    at each point, and the consequences each choice
    leads to. For instance, there are five options
    for who goes across first: one wildebeest, one lion, two wildebeest, two lions, or one of each. If one animal goes alone, it’ll just have to come straight back. And if two wildebeest cross first, the remaining one will immediately
    get eaten. So those options are all out. Sending two lions, or one of each animal, can actually both lead to solutions
    in the same number of moves. For the sake of time,
    we’ll focus on the second one. One of each animal crosses. Now, if the wildebeest stays
    and the lion returns, there will be three lions
    on the right bank. Bad news for the two remaining wildebeest. So we need to have the lion
    stay on the left bank and the wildebeest go back to the right. Now we have the same five options, but with one lion
    already on the left bank. If two wildebeest go,
    the one that stays will get eaten, and if one of each animal goes, the wildebeest on the raft
    will be outnumbered as soon as it reaches the other side. So that’s a dead end, which means that at the third crossing, only the two lions can go. One gets dropped off, leaving two lions on the left bank. The third lion takes the raft back to
    the right bank where the wildebeest are waiting. What now? Well, since we’ve got two lions waiting
    on the left bank, the only option is for two wildebeest
    to cross. Next, there’s no sense in two wildebeest
    going back, since that just reverses the last step. And if two lions go back, they’ll outnumber the wildebeest
    on the right bank. So one lion and one wildebeest
    take the raft back leaving us with one of each animal
    on the left bank and two of each on the right. Again, there’s no point in sending
    the lion-wildebeest pair back, so the next trip should be either
    a pair of lions or a pair of wildebeest. If the lions go, they’d eat the wildebeest
    on the left, so they stay, and the two wildebeest cross instead. Now we’re quite close because the
    wildebeest are all where they need to be with safety in numbers. All that’s left is for that one lion
    to raft back and bring his fellow lions over
    one by one. That makes eleven trips total, the smallest number needed
    to get everyone across safely. The solution that involves sending both
    lions on the first step works similarly, and also takes eleven crossings. The six animals escape unharmed
    from the fire just in time and begin their new lives
    across the river. Of course, now that the danger’s passed, it remains to be seen how long their
    unlikely alliance will last.

    How do schools of fish swim in harmony? – Nathan S. Jacobs
    Articles, Blog

    How do schools of fish swim in harmony? – Nathan S. Jacobs

    August 25, 2019


    How do schools of fish swim in harmony? And how do the tiny cells in your brain
    give rise to the complex thoughts, memories, and consciousness that are you? Oddly enough, those questions have
    the same general answer: emergence, or the spontaneous creation of
    sophisticated behaviors and functions from large groups of simple elements. Like many animals,
    fish stick together in groups, but that’s not just because
    they enjoy each other’s company. It’s a matter of survival. Schools of fish exhibit
    complex swarming behaviors that help them evade hungry predators, while a lone fish is quickly singled out
    as easy prey. So which brilliant fish leader
    is the one in charge? Actually, no one is, and everyone is. So what does that mean? While the school of fish is elegantly
    twisting, turning, and dodging sharks in what looks
    like deliberate coordination, each individual fish is actually
    just following two basic rules that have nothing to do with the shark: one, stay close, but not too close
    to your neighbor, and two, keep swimmming. As individuals, the fish are focused on
    the minutiae of these local interactions, but if enough fish join the group,
    something remarkable happens. The movement of individual fish
    is eclipsed by an entirely new entity: the school, which has its own
    unique set of behaviors. The school isn’t controlled
    by any single fish. It simply emerges if you have enough fish
    following the right set of local rules. It’s like an accident that happens over
    and over again, allowing fish all across the ocean
    to reliably avoid predation. And it’s not just fish. Emergence is a basic property of many
    complex systems of interacting elements. For example, the specific way in which
    millions of grains of sand collide and tumble over each other almost always produces the same
    basic pattern of ripples. And when moisture freezes
    in the atmosphere, the specific binding properties
    of water molecules reliably produce radiating lattices
    that form into beautiful snowflakes. What makes emergence so complex is that you can’t understand it
    by simply taking it apart, like the engine of a car. Taking things apart is a good first step
    to understanding a complex system. But if you reduce a school of fish
    to individuals, it loses the ability to evade predators, and there’s nothing left to study. And if you reduce the brain
    to individual neurons, you’re left with something that is
    notoriously unreliable, and nothing like how we think and behave, at least most of the time. Regardless, whatever you’re thinking about
    right now isn’t reliant on a single neuron
    lodged in the corner of your brain. Rather, the mind emerges from
    the collective activities of many, many neurons. There are billions of neurons
    in the human brain, and trillions of connections between
    all those neurons. When you turn such a complicated
    system like that on, it could behave in all sorts
    of weird ways, but it doesn’t. The neurons in our brain follow
    simple rules, just like the fish, so that as a group, their activity
    self-organizes into reliable patterns that let you do things
    like recognize faces, successfully repeat the same task
    over and over again, and keep all those silly little habits
    that everyone likes about you. So, what are the simple rules
    when it comes to the brain? The basic function of each neuron
    in the brain is to either excite or inhibit
    other neurons. If you connect a few neurons together
    into a simple circuit, you can generate rhythmic patterns
    of activity, feedback loops that ramp up
    or shut down a signal, coincidence detectors, and disinhibition, where two inhibitory neurons
    can actually activate another neuron by removing inhibitory brakes. As more and more neurons are connected, increasingly complex patterns
    of activity emerge from the network. Soon, so many neurons are interacting
    in so many different ways at once that the system becomes chaotic. The trajectory of the network’s activity
    cannot be easily explained by the simple local circuits
    described earlier. And yet, from this chaos,
    patterns can emerge, and then emerge again and again
    in a reproducible manner. At some point, these emergent
    patterns of activity become sufficiently complex, and curious to begin studying
    their own biological origins, not to mention emergence. And what we found in emergent phenomena
    at vastly different scales is that same remarkable
    characteristic as the fish displayed: That emergence doesn’t require
    someone or something to be in charge. If the right rules are in place, and some basic conditions are met, a complex system will fall into
    the same habits over and over again, turning chaos into order. That’s true in the molecular pandemonium
    that lets your cells function, the tangled thicket of neurons
    that produces your thoughts and identity, your network of friends and family, all the way up to the structures and
    economies of our cities across the planet.

    The Atlantic slave trade: What too few textbooks told you – Anthony Hazard
    Articles, Blog

    The Atlantic slave trade: What too few textbooks told you – Anthony Hazard

    August 23, 2019


    Slavery, the treatment of human beings as property,
    deprived of personal rights, has occurred in many forms
    throughout the world. But one institution stands out for
    both its global scale and its lasting legacy. The Atlantic slave trade, occurring from the late 15th
    to the mid 19th century and spanning three continents, forcibly brought more than 10 million Africans
    to the Americas. The impact it would leave affected
    not only these slaves and their descendants, but the economies and histories
    of large parts of the world. There had been centuries of contact
    between Europe and Africa via the Mediterranean. But the Atlantic slave trade
    began in the late 1400s with Portuguese colonies in West Africa, and Spanish settlement
    of the Americas shortly after. The crops grown in the new colonies,
    sugar cane, tobacco, and cotton, were labor intensive, and there were not enough settlers
    or indentured servants to cultivate all the new land. American Natives were enslaved,
    but many died from new diseases, while others effectively resisted. And so to meet the massive
    demand for labor, the Europeans looked to Africa. African slavery had existed
    for centuries in various forms. Some slaves were indentured servants, with a limited term
    and the chance to buy one’s freedom. Others were more like European serfs. In some societies, slaves could
    be part of a master’s family, own land, and even rise
    to positions of power. But when white captains came offering
    manufactured goods, weapons, and rum for slaves, African kings and merchants
    had little reason to hesitate. They viewed the people they sold
    not as fellow Africans but criminals, debtors,
    or prisoners of war from rival tribes. By selling them, kings enriched
    their own realms, and strengthened them
    against neighboring enemies. African kingdoms prospered
    from the slave trade, but meeting the European’s massive demand
    created intense competition. Slavery replaced other criminal sentences, and capturing slaves
    became a motivation for war, rather than its result. To defend themselves from slave raids, neighboring kingdoms
    needed European firearms, which they also bought with slaves. The slave trade had become an arms race, altering societies and economies
    across the continent. As for the slaves themselves,
    they faced unimaginable brutality. After being marched
    to slave forts on the coast, shaved to prevent lice, and branded, they were loaded onto ships
    bound for the Americas. About 20% of them
    would never see land again. Most captains of the day
    were tight packers, cramming as many men
    as possible below deck. While the lack of sanitation
    caused many to die of disease, and others were thrown
    overboard for being sick, or as discipline, the captain’s ensured their profits
    by cutting off slave’s ears as proof of purchase. Some captives took matters
    into their own hands. Many inland Africans
    had never seen whites before, and thought them to be cannibals, constantly taking people away
    and returning for more. Afraid of being eaten,
    or just to avoid further suffering, they committed suicide
    or starved themselves, believing that in death,
    their souls would return home. Those who survived
    were completley dehumanized, treated as mere cargo. Women and children were kept above deck
    and abused by the crew, while the men were made to perform dances in order to keep them exercised
    and curb rebellion. What happened to those Africans
    who reached the New World and how the legacy of slavery
    still affects their descendants today is fairly well known. But what is not often discussed is the effect that the Atlantic slave trade
    had on Africa’s future. Not only did the continent lose
    tens of millions of its able-bodied population, but because most of the slaves
    taken were men, the long-term demographic
    effect was even greater. When the slave trade was finally
    outlawed in the Americas and Europe, the African kingdoms whose economies
    it had come to dominate collapsed, leaving them open
    to conquest and colonization. And the increased competition
    and influx of European weapons fueled warfare and instability
    that continues to this day. The Atlantic slave trade also contributed
    to the development of racist ideology. Most African slavery had no deeper reason
    than legal punishment or intertribal warfare, but the Europeans
    who preached a universal religion, and who had long ago
    outlawed enslaving fellow Christians, needed justification for a practice so obviously at odds
    with their ideals of equality. So they claimed that
    Africans were biologically inferior and destined to be slaves, making great efforts
    to justify this theory. Thus, slavery in Europe and the Americas
    acquired a racial basis, making it impossible for slaves
    and their future descendants to attain equal status in society. In all of these ways, the Atlantic slave trade
    was an injustice on a massive scale whose impact has continued
    long after its abolition.