Recent comments in /f/askscience

2011StlCards t1_j412mtv wrote

Reply to comment by coob in Why are coastlines crinkly near the poles but smooth in the tropics? by emsot

North American natives were effectively isolated from the rest of the world until the 15th century.

Europe, Africa, the Middle East, China, India, and southeast Asia had basically all been interconnected for millenia.

You had the Roman empire, the hellenestic kingdoms, Mongolian empire, trade routes of the Indian Ocean, trade routes like the Silk Road, etc... that had people, goods, and ideas transferring from one group to another for centuries.

That means technology, religion, science, and more from China can make it to Europe and have influence.

The Americas had some civilizations that were pretty damn advanced. The Inca somehow made a huge empire in the mountains with only humans and llamas. The Aztec basically had a capital that rivaled any city in europe at the time of its destruction.

If given time, these groups may have become more powerful, but the odds were against then when it came to trade and new ideas. There just weren't as many people involved there as in the Eurasian trade networks

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mtv2002 t1_j411xau wrote

Reply to comment by byfpe in Why do poultry producers kill their stock when they get bird flu, rather than keeping survivors to reproduce? by poorbill

Former chicken farmer here. Not only do they destroy my flock but they will euthanize any flock within a certain mile radius. So if my neighbors farm gets it, mine is destroyed. It's very deadly to chickens and contagious, that's why we take bio security so seriously. My farm is off limits to anyone other than myself and a flock advisor and the feed trucks, picking crew etc. We also have bleach pans at every door we have to step onto before entering the houses. Also any "visitors" have to sign in and wear over shoes as to not contaminate the houses. Plus they leave the euthanized flock in the house in a big pile to compost for a while to make sure the Temps get high enough to kill any remaining viruses. Point is that getting bird flu once will pretty much bankrupt a farm because you can't have a new flock for 6 months or so.

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2011StlCards t1_j411p3z wrote

Reply to comment by CorrectCoyote926 in Why are coastlines crinkly near the poles but smooth in the tropics? by emsot

u/Baxters_keepy_ups already basically stated exactly what I was going to write.

Up until about the 16th to 17th century, Europe was not the world superpower that it would become.

The idea goes that Europe was able to advance in technology and power pretty quickly because of the interconnectiveness of the people on the continent

Large, navigable rivers. Arable land. Beasts of burden (i.e., horses, donkeys, camels). Deepwater ports (for trade). All of these aspects help to advance trade and, thus the connections between groups.

When large groups of people have connections like that, ideas and technology flow from one group to the next.

When you have that interplay between people (i.e. trade), you theoretically would advance quicker since someone in Portugal may have a ship design that is more efficient that the French may get to see and create for themselves or trade for.

It also helps that most of the large European powers had languages of either romance or Germanic origins, which makes talking to one another even easier.

This doesn't preclude conflict, of course, as we see countless European wars between neighbors throughout history. But between those conflicts, trade reigns Supreme.

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iayork t1_j40yl4x wrote

Reply to Why do some people get infected with HIV, while others do not, although both groups have been exposed to the virus? by Terradubia

This is really the same question as "Why do some people catch COVID and some not?" or "Why did I not get measles when my brother did?"

The answer is going to disappoint you: It's chance.

The odds of getting infected with anything is a combination of the amount of the pathogen, the environmental conditions, and the personal resistance. Are you exposed to a huge amount of pathogen, in optimal conditions, when you're under immunosuppressive treatment for an organ transplant? Pretty good chance you'll be infected. Are you exposed to a very small amount of respiratory pathogen, in a place with great ventilation, after you've been vaccinated? Pretty good chance you won't be infected.

But none of these are absolute on/off switches. If you were to look at exposure levels, you'd see a bell curve (a normal distribution) -- the sign that there are many influences on the factor. If you were to somehow plot your resistance levels, you'd see a bell curve. Same for environmental conditions. You're not adding together three on/off switches, you're adding together three complex pathways and getting a fourth complex pathway out of it.

Of course the bell curve can shift right or left. If you're exposed to someone with measles, you're probably exposed to much more pathogen than the minimal infectious dose - the pathogen curve is shifted over to the left. But if you're vaccinated with the very effective measles vaccine, your personal resistance is extremely high - the resistance curve is way over to the right. Still, measles vaccine is "only" 99% effective -- there's still a chance you can be infected.

With HIV, then, you can think about the three components of risk. If you were unfortunate enough to receive a blood transfusion from an infected person, then the pathogen dose would likely be high, the environment (blood stored carefully to keep the cells happy) would be ideal for the virus, and personal resistance would be very low because it's bypassed many protective levels. The chance of infection would be pretty high.

If you're exposed by sexual contact, the dose of virus is much lower. There are many more layers of protection (intact skin or mucous membranes, innate immune protection). The environment isn't ideal for the virus. You end up with a lower chance of infection, but not zero.

Of course there are situations where one or more of the three components does drop to zero, or nearly so. You're constantly exposed to vast doses of Pepper mild mottle virus, but there's no amount of PMMoV that will harm a human -- that pathogen risk is zero. There are genetic variations that might make someone extremely resistant to HIV -- that person's individual risk is nearly zero. (At this point someone is about to jump in and claim that that variation was driven by the Black Death, which isn't true. See previous posts.)

But for viruses that are medically relevant to humans, the reason they're relevant is that those three risk curves aren't set to zero, and that means it becomes an odds game. People who try to prevent diseases are aiming to moving those odds in our favor, perhaps through vaccination (resistance curve) or ventilation (the environment curve) or masking (reducing the pathogen curve) or, usually, some combination of all of them. You may never reduce everything to zero, but even reducing each of them by 50% can lead to an overall major win.

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krashlia t1_j40u4oz wrote

Reply to comment by poorbill in Why do poultry producers kill their stock when they get bird flu, rather than keeping survivors to reproduce? by poorbill

Its like the coronavirus, when the pandemic started. Each and everytime someone reported that "a case" appeared, I was certain that there were actually 10 more than that. Once a virus shows up in a population, you'll only notice some people showing symptoms within a certain amount of time, while others simply haven't displayed signs of infection yet.

At some point, Containment of the disease can only go so far, unless you're willing to use ever more force to keep people in place (since they'll characteristically refuse to do what they're told), or just straight-up kill them to save the rest of the population.

But, people aren't chickens.

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