Thread by @krishashok

What connects beer, reptiles basking in the sun, a dangerous yeast infection, 98.4 Fahrenheit, an asteroid collision and finally, coconut toddy? A thread.

It begins with the beer - what single invention made the industrial production of beer possible? Of course, mankind has been brewing beer for millennia, and even now, some of the finest beer is made in monasteries using methods that have not changed for a thousand years.

The answer is the thermometer. You see, it’s one thing to make small batches of beer in a monastery but a wholly different enterprise to brew hundreds of millions of bottles of beer that taste exactly same

If brewing was a simple chemical process involving standardized chemicals, no problems, but it is fermentation and involves plants and fungi, and biological processes are notoriously hard to standardise. Temperature control plays a huge role in brewing.

The key, it turned out in the 18th century, was the invention of an accurate thermometer by Daniel Gabriel Fahrenheit, and rather crucially, its initial game-changing use in medicine.

In fact, one of the pioneers of industrial brewing, Michael Combrune who was the first to use thermometers to brew beer, was influenced by the papers of Dr Hermann Boerhaave, who pioneered the use of thermometers to detect illnesses

And that brings us to 98.4 Fahrenheit - the temperature we consider to be, on average, "normal" temperature. The use of thermometers in hospitals saved millions of lives. But we shall ask a more interesting question - why 98.4? Why not higher or lower than that?

In fact, all mammals have an internal temperature in the range of 98.4 to 98.6 F, so it begs the question - why? Would a slightly lower temperature not save us a ton of energy? Keeping our body temperature takes most of the energy we consume as food.

But to answer the question of why evolution didn't select for mammals with lower body temperatures, we need to take a quick diversion back to our (mostly) friendly, beer-brewing and bread-baking microbe, yeast.

In the early 2010s, there was a rather mysterious outbreak of a surprisingly lethal yeast infection in multiple places in the world at around the same time, thus ruling out transmission by human travel.

Turns out that the yeast that was causing this was Candida auris, and to understand why it was suddenly resurfacing in the 2010s, we need to go back in time by 66 million years to the Yucatan peninsula in what is today Mexico.

One day, 66 million years ago, an asteroid collided with our planet in the Yucatan peninsula and wiped out three-quarters of all life on the planet. In fact, it’s estimated that no animal over 25 kgs survived.

Among the animals that survived this apocalypse were these tiny, shrew-like underground things that were some of the earliest known mammals.

One of these female shrews was, to quote the Radiolab episode where I heard it, the great great great great great great great great great great great great great great great great great great great great great great great great...grandmother of every human on the planet today

So this brings us to our next question - while that collision killed off the large dinosaurs, clearly some reptiles survived - turtles, tortoises & crocodiles, for instance. But why don’t reptiles dominate the planet today?

And the reason why experts felt that it was mysterious that surviving reptiles did not dominate the post-apocalyptic landscape back then is, well, 98.4 F. Reptiles are cold-blooded and don't spend energy maintaining high body temperatures

And the thinking was - surely there was a massive shortage of food in the decades and centuries after the impact, so logic dictates that a cold-blooded turtle had a better chance than a warm-blooded shrew that needs to eat 3 meals a day

A crocodile could eat one large meal and then chill out, basking in the sun for several days before needing to eat again. So why did the mammals win? Turns out, we have to go back to our friendly microbe again - Yeast.

One thing we should be familiar with fungi is that they like colder temperatures and hate warm temperatures. This is why reptiles, who cannot maintain high temperatures internally, bask in the sun. They heat up their bodies in the sun to prevent fungal infections.

And guess what is also in short supply after an asteroid impact? Sunlight. It was, in effect, a nuclear winter thanks to the dust from the impact blocking sunlight for potentially a very long time.

And guess who likes low temperatures, low sunlight and large, lazy reptiles that can't maintain high body temperatures? Fungi.

So, it was a double whammy for reptiles. The larger dinosaurs were wiped out by the impact, and the ones that survived had a tough time dealing with fungal infections, while mammals that were just warmer than fungi's preferred temperature survived to tell this tale

Mammals slowly started dominating the planet and here we are. Sipping craft beer brewed with precision thermometers used by doctors to measure 98.4F, the temperature that keeps yeast infections at bay.

And of course, that’s not the end of the story. It turns out that, at least in the west, average body temperatures are going down. In many places, kids now have 97.5F or lower as average temperatures, and there are many reasons for this.

Lower metabolic rates, overall reduction in instances of inflammation due to better medical care etc. If we don’t get infected as often as used to in the past, we don’t need to maintain a high temperature, it turns out.

But what this means is that a Candida auris yeast, with the genetic memory of 66 million years is now realising that, like reptiles in the post-apocalyptic world back then, humans with a lowered body temperature are fair game.

I realise this is not the kind of scaremongering one needs in the middle of a pandemic, but relax. Our body temperatures aren’t falling that fast, and unlike viruses, we know how to cure fungal infections.

And while many states in India right now have stopped the supply of beer, you can take some yeast, drop it into coconut water, add some sugar and make some fizzy coconut toddy for yourself in 48 hours.

On that note, If you are free this Saturday evening, join me for a chat on the science of Indian cooking at Pune Science on Tap at 7 PM IST this Saturday (12th September)

And while you are at it, please pre-order Masala Lab: The Science of Indian Cooking here - amazon.in/dp/0143451375

Sources
1. "Fungus Amungus" by Radiolab - wnycstudios.org/podcasts/radio…
2. History of Brewing - breweryhistory.com/journal/archiv…
3. Dinosaur Extinction - en.wikipedia.org/wiki/Cretaceou…

PS: When I use the term "realize" in the context of fungi, it's a rhetorical device, and does not imply that fungi have some kind of malicious intent here. They don't.