Will you ever meet ET?

By Andrew Anderson (@AndersonEvolve)

One of my favorite shows is Firefly−if you haven’t heard of it, check it out. An aspect of the show I found enjoyable was, despite being science fiction, it explicitly stated there were no known aliens across the regions humans had expanded to. The thought of seeing the results of evolution on another planet would be amazing, and the mental games trying guess at what that life might look like are enjoyable. In reality though, I don’t think we will ever encounter alien life*, much less intelligent life, for a long while (>1000s of years) if at all. I am hardly the first to make such a claim, but I would like to bring up some of the reasons I don’t think we’ll encounter extraterrestrials within anyone’s lifetime.

The best place to start is with Drake’s Equation (see link for details), it’s basically a probabilistic statement made up of dependent chance events and time components. 

eq

Therefore, the chance of each successive event is multiplied by the previous then multiplied by the time that all chance events have occurred. As you can see the Drake Equation includes 6 conditions that have to be met, making the odds of an outcome lower with each condition (e.g. rolling a 1-5 on a die occurs ⅚ of the time, but doing it 6 successive times happens ~⅓ of the time). What’s more, we have no idea what the probabilities are for the later parts of the equation. The rate of star formation and the fraction of stars with planets are able to be reasonably estimated. Everything else is challenging to define. The big issue is we have a sample size of 1. We only know of one planet that formed life, evolved intelligent life, and sent signals−Earth. This is a two-fold problem. If I drew a number at random, what was the probability of drawing that number? Without knowing either how many draws it took or what range of numbers I had to choose from, you cannot know. Additionally, we now have what is known as a sample bias. While we are piecing together how life got started here, is that the ONLY way? Once life begins developing on a planet, what is the likelihood intelligent life appears? We might conclude it’s 100% given what happened on Earth, but remember the majority of Earth’s history is dominated by non-intelligent life*. Humans are a relative blip on the history of life and there’s no evidence that other groups evolved intelligent life. Were it not for a well-timed meteor, there still might not be intelligent life. All of this is to say, we’re not sure how to define all the portions of Drake’s Equation, so anyone claiming it supports their idea (even one saying it’s not possible) is on unstable ground.

Now we can get into some fun probabilistic concepts. Drake’s Equation doesn’t offer much help, but it comes down to a fairly simple question: is Earth, and the process of life on it, rare or common? Some would invoke the mediocrity principle, that is if you only have one observation, it is more likely you observed a common event than a rare one. Imagine it’s your first time snorkeling on a reef; the fish you see are probably the more common fish on the reef. The problem with this is, since we are alive, we had to come from a planet that met the criterion for life, so there is no way our limited observations would NOT include a planet with life on it. I actually think life on Earth could be more along the lines of the Wyatt Earp Effect; given the amount of attempts (planets in this case) it is an almost certainty that 1 will hit on the rare event. Wyatt Earp was notorious for winning gun fights without getting hurt, but given the number of gunfighters and gunfights, someone had to survive multiple gun fights through sheer luck. So life forming could be rare, but it happened at some point and, since we’re here, we see that outcome.

My point so far is we have no idea what the odds of life are, and I acknowledge that my suspicion it’s rare is just that, a suspicion. I think life likely does exist somewhere else out there, but we won’t see it anytime soon because: physics. Let’s assume there is a planet we want to check out for life. There’s a candidate at our nearest star ~4 light years away. Let’s assume that we have a spacecraft right now capable of traveling ~2% the speed of light, the current record is ~1.5%. That means it would take 200 years to reach the planet, plus 4 more just to hear if they found anything. Even if we hit on our first pass, it still wouldn’t happen in our lifetime. Our ability to detect non-sentient life is severely limited and there are no ways to be certain other than direct exploration.

Instead we would have to hope that lifeforms on another planet are sending some signal we can detect, which means they are likely intelligent, or they are likewise looking for life*. Radio waves are electromagnetic waves and travel at the speed of light but there is a delay. Try to imagine a conversation on Messenger where you only see what was written 4 years ago, that’s what it would be like to converse with our nearest star (Alpha Centari could only now tell us how they felt about Lost). This also makes Sci-Fi movies amusing with how communication and observation of events unfold (think about every intense radio conversation in space and how far apart they were–likely they were getting that message minutes or hours after it was sent). Humans have only been sending out signals for ~100 years which means only things 50 light years away could be responding at this point (travel to and from) which is 1/2000 of the distance of the Milky Way. We’ve only been listening for 50 years which means some civilization has to be sending signals at the right time to have them reach Earth in this exact range of listening time*. Consider a planet looking at Earth but is on the other side of the Milky Way, they would not find anything and have to wait 100,000 years just to hear it. All of this assumes we know what to look for or what to broadcast.

In order for us to find life it would have to be close, sentient, and signaling. While the universe is incredibly large, we’ve now severely narrowed our search window, which means life has to form easily and evolve intelligence frequently if we are to see it while you and I are here. I just don’t think that probable. Got something to add or something I missed?* Give me tweet!

Post-Script:

Scott Mattison (@FoolsPizza) added some thoughts (* in text, his thoughts in italics) that should be shared and responded to (my thoughts in bold).

  • I imagine we will find microbial life on colonized planets. I mean, we think we might have bacterial life on other planets in our local system This seems most likely, although we don’t have every step down for the formation. What we do know doesn’t seem like something any other planet would have gone through in its formation. 
  • Non-intelligent or non-sentient or just not up to our levels. It could be reasonably argued multiple forms of sentient life developed on Earth. Humans just won the competition. (Neanderthals vs. Homo sapiens). Also there is the question of intelligence level of apes and dolphins which clearly can learn communicative behaviors In this context I equate intelligence with the ability to send and detect signals to space. This is not at all the correct definition, but for a short piece it’s the easiest term I can think of. Yes, this means humans didn’t become intelligent until quite recently.
  • Fermi paradox –It starts with supposition that life is common and we should see them. I don’t agree with the premise.
  • This gets even worse. EM waves decrease intensity as they spread out through space through the inverse square law (not that inverse square law, the other one).Essentially intensity decreases on the order of distance squared. So even if someone is screaming out into space. They have to scream really loud to appear over the background noise and be screaming in our direction (although we can get pretty sensitive detection especially if they are sending out patterned signals). −Neat.
  • We could also see visible signs from ancient, more advanced races. Concepts of super structures that utilize the energy of their local star would be observable. (we have had some pretty well publicized incorrect interpretations of these things). −It’s still a matter of timing, the ancient civilizations had to have formed at just the right time for us to see, or the structures are durable enough to keep going.  I guess the fun question is does intelligent life persist once it is formed?

How do we Hear?

By Scott Mattison (@FoolsPizza)

Hearing is one of the five traditional senses, but by the time individuals reach 60 years old, one in three will develop significant hearing loss in one or both ears. To treat this hearing loss, we must first have a basic understanding of how sound and our hearing work.

Sounds travel by mechanical vibrations of particles that contact one another. Air, water, and solids all allow for these vibrations to occur; however, in space, no one can hear you scream because outer space is a vacuum with no small particles to transfer sound (sorry Star Wars fans).

The ear is divided into three regions: the outer ear, the middle ear, and the inner ear. The outer ear is what is most familiar to people, it consists of what we traditionally call ears and a canal that leads to the eardrum. The role of the outer ear is to collect sound and direct it to the middle ear through the ear drum. The unique shape of the ear enables directed sensing of sounds which gives people the ability to determine where sounds come from.

850px-Auditory_ossicles-en.svg
A nice illustration of the middle ear bones (ossicles). Courtesy of Wikipedia.

The middle ear is an open, air filled space in the skull that separated from the outer ear by the ear drum. The active portion of the middle ear consists of three bones known as the malleus, incus, and stapes. The malleus is attached to the eardrum, and when the eardrum vibrates in response to sounds, those vibrations are transferred to the malleus. Movements of the malleus move the incus, which in turn move the stapes. The stapes then vibrates against what is called the oval window of the inner ear. The bones of the middle ear form a lever arm that provides an amplification of sound by around 130%. Additional amplification occurs due to the size difference between the eardrum and the oval window of the inner ear. Overall, sound vibrations entering the inner ear are around 18 times larger than sound vibrations against the eardrum. The middle ear also has special muscles that when activated will reduce the intensity of loud sounds. This is called the acoustic reflex and may reduce sound intensity by around a factor of 10. The acoustic reflex protects the delicate structures of the inner ear.

The inner ear is where all the magic of hearing happens. The inner ear takes the mechanical vibrations of sounds and converts them into electrical impulses within the brain. How this actually works is both a lot cooler and a lot more complicated than it might seem.

At their best, humans can hear a range of sound frequencies (think notes on the piano, each note is a different frequency) between 20 Hz and 20,000 Hz. 20 Hz is a really deep bass sound and 20,000 Hz (If you can still hear it) is an extremely high pitched whine. As we age, sensory cells in our inner ear begin to die and we lose the ability to hear higher pitched frequencies. By age 20, most males have lost the ability to hear 20,000 Hz, females typically begin to lose higher frequency hearing later into their twenties. Fortunately most of human communication is limited to the 100s of Hz frequency range. The fact that we can differentiate between sounds of different frequencies means that our inner ear has to respond differently to different sound waves.

Nervous cells have a recovery period of 1 – 5 ms after each time they fire, meaning the fastest a nerve could respond is 1000 Hz. If this is true, how can our ears generate nervous signals in response to sounds vibrating up to 20 times faster? The answer to this question is a fun word: Biomechanics. The inner ear, known as the cochlea, consists of 3 fluid-filled tubes that spiral up to a blind end. Typically this is drawn as its own snail-shaped solid, but in reality the cochlea is a fluid filled cavity with the temporal bone of the skull. Sounds enter the cochlea through the oval window into the bottom of the 3 tubes. Sound waves travel to the top of the spiral of the cochlea then back down through the top tube and vibrate against the oval window. This top tube and bottom tube mainly play the role of sound conductor; the nervous tissue is all sitting within the middle tube.

Inner Ear
A rough sketch of the cochlea with the spiral stretched out into a strait line. Sound waves enter through the oval window.  Higher frequency sounds are propagated through the basilar membrane toward the start of the cochlea whereas lower frequency sounds pass through the basilar membrane toward the end.

Between the bottom tube and the middle tube is what is called the basilar membrane. This membrane has changing mechanical properties all the way down its length so that at the entrance of the cochlea it vibrates strongly in response to higher frequency sounds and at the top of the spiraled cochlea the basilar membrane vibrates best in response to lower frequency sounds. Nervous cells in the inner ear respond to the movement of the fluid within that middle tube so when the basilar membrane vibrates more strongly due to higher frequency sounds at the base of the cochlea, the nervous cells in that region know to tell the brain that you just heard a high pitched sound. And when nervous cells respond to movement in the upper part of the cochlea, the brain knows you just heard a lower pitched sound.

1251px-Organ_of_corti.svg
An illustration of what is known as the organ of Corti. This rests on top of the basilar membrane and plays a large role in our hearing. Image source: Wikipedia.

The basilar membrane is a really cool example of biomechanics in of the body solving complex challenges, and Georg von Békésy even won the Nobel Prize in Physiology or Medicine in 1961 for his work in in demonstrating its function. However, movement of the basilar membrane alone does not completely account for how well the hearing of humans and other mammals can tell the difference between two frequencies. This is the role of the organ of Corti, which I will introduce in a later blog post. Obviously, there is a bit more to the inner ear than I have explained here, and this is an exciting question for which scientists are still exploring answers!

 

Are Koopas Sex-Role Reversed?

By: Andrew Anderson (@AndersonEvolve)

In my previous post, I presented what koopas are and what forms (phenotypes) are considered the same species.  Of course, after the post I found this page, which lists what character types are within the koopa species complex.  The bad news is I missed a couple—I had no idea there were so many Mario games. The good news is the ones I designated as koopas are on the list and honestly it’s all made up anyways.  In addition, the groups I failed to include aren’t necessary to determine the parental and mating system of koopas.

The first question—what kind of parental care do koopas have?— is straightforward in its answer:  male brood care. Running down the list of familial relations and we see Koops has a father, Koopley, Kolorado has a father, Koopa Krag is a grandfather, and Bowser is just a prolific father.  Notice something missing? No mention of mothers. Even Baby Bowser’s caretaker is Kamek. Now we can debate as to how dedicated these fathers are since most of the time the father is absent, but in most cases the father has some interest in the well-being of his children.  We do know female koopas exist, so why aren’t they seen with offspring? Quite simply, females don’t participate in broodcare, leaving males with those duties. It is true we can’t sex most koopas, but I think that’s because they haven’t reached maturity yet and address that below.  Such a conclusion means that the Koopa Troop is sending young koopas into battle that Mario mercilessly pounds on.

The next question—which sex is under stronger sexual selection (more intense competition for mating and producing offspring)?—is a bit more challenging to answer.  There has been some discussion among biologists about how best to measure and determine sexual selection, but this paper has a good description and mathematical explanation for those who want a little more. I’ve gone over the various things known about koopas and honestly can’t come to a certain conclusion, so I’ll just lay out the evidence for both sides.

Typical sex-roles–Stronger Male Sexual Selection

There are three pieces of evidence that supports the typical sex-roles for koopas.  The first is the variance in reproductive success. Bowser has a bunch of kids, while the other known fathers seem to just have one.  Unequal reproductive output creates opportunities for sexual selection. Bateman proposed that males mating with more females lead to more offspring, but more matings does not produce more offspring in females.  A quick glance across all of Bowser’s kids from Mario 3 and there is a wide variety of forms, suggesting that they may have different mothers. There seems to be some male koopas who mate A LOT, some who mate a little, and some who don’t mate; a clear indication that males could be under sexual selection.

hairkoopa
Male koopas with maturation (secondary sex?) trait of hair. Notice the prolific Bowser’s luxurious locks. Left:  Koopley–Koops father, Top:  Koopa Krag, Bottom:  Bowser

The other evidence is koopas seem to have secondary sexual characteristics.  Look at the known fathers in koopa-dom and the non-fathers. Notice that the fathers have hair, I propose that hair is a trait that shows the males are ready to mate, much like antlers on deer.  Now, there are koopas with hair that don’t have any (known) offspring, but it could be that they are in mating condition but have not found a mate or produced any offspring yet. The more important aspect is there are no successful males without hair.  While there are other traits, like a spiked shell and horns that Bowser has, no other fathers have them and there are other koopas that posses spikes and horns without children, so these traits may not play a role in reproductive success (Bowser is attractive because of his long flowing hair).

immature
Koopas without hair and no known offspring. None of these koopas are mature.

Lastly, the dearth of females suggests the sex ratio is tilted towards males.  In cases where one sex is rarer than the other,the rare sex is able to be choosier about their mate, putting selection on the majority sex.  In most species the split of sexes is 50/50 so the better descriptor is Operational Sex Ratio (OSR) and it counts only individuals who are reproductively available. If one sex takes longer to mature or is engaged in broodcare/pregnancy, it doesn’t count.  Even though male koopas take part in broodcare, Bowser demonstrates that they can brood from multiple females so they aren’t removed from the OSR calculation (something that is common in fishes).

Reversed Sex-Roles: Stronger Female Sexual Selection

So while I have assumed Bowser has lots of kids from multiple females, it is currently Nintendo’s stance that he only has one child–Bowser Jr.  Personally, I disagree since the Koopa Kids and the Koopalings have been called his children in previous games. In any case, if Bowser only has one child then the variance in offspring across males drops precipitously.  Now the number of children any male koopa has is either 1 or 0, which isn’t much variance. In this case, the males don’t seem to get more offspring from multiple females (i.e., little opportunity for sexual selection). This doesn’t mean females are higher, but it certainly undercuts the evidence for males.

300px-Koopalings_-_New_Super_Mario_Bros_U
Koopalings.  Notice the wide variety of forms.  It seems unlikely that all were made from the same pairing.

Alternatively, Bowser could be cuckolded with the possibility he was given all his children by one female although not all of them he sired.  This is known to happen in some polyandrous (multiple males one female) mating systems such as sandpipers and jacanas. The result is Bowser mated with one female, who mated with multiple males, that gave him seven eggs (the Koopalings) for him to care for.  Certainly if you were to look at all the Koopalings many of them bear little resemblance to the King of Koopas. Without genetic tests, we have no way to know the true parentage and thus the mating system for sure–although it would make for a great Maury episode.

female
Female Koopas.  From Left to Right and Top to Bottom:  Pom Pom, Koopie Koo, Wendy O. Koopa, Lakilulu, Kammy Koopa, Holly Koopa, Kylie Koopa.  Notice the females with hair either have a mate or are considered mature. 

Just as reproductively active male koopas have hair, it appears females have the same trait to indicate maturation.  Take a look at the 7 named female koopas: Koopie Koo, Lakilulu, and Pom Pom all have boyfriends and have hair. Holly, Kylie, and Wendy O Koopa are not shown with love interests and do not have hair.  Kammy Koopa has hair and has no shown boyfriend, but given her apparent age she is likely mature. Since both males and females have hair it can’t be a secondary sex trait (it has to be different between the sexes to be a sex trait), but it can be a sign of maturation.  

Both Lakilulu and Koopie Koo are extremely protective of their boyfriends, perhaps this is similar to mate guarding if females are under stronger selection.  While Koopie Koo’s boyfriend, Koops, is not mature (no hair), she encourages him to adventure and come back a stronger koopa. It may be she has secured a mate and wants to be sure he is ready to provide care, a long term strategy if ever there was one.  So why are the female so protective of their mates? We can go back to the operational sex ratio; if males are engaged in brood care and not many are mature yet (very few have hair) then there are less males than females available for mating thereby forcing females to protect the mates they have found.

I would like to point out that it is entirely possible, and even not uncommon, for both sexes to experience sexual selection.  When we talk about the roles though, we are asking which sex undergoes greater selection than the other as that can drive how evolution works.  While I’m not certain, I would like to think the females are under stronger selection; but then again I work with reversed species so I’m biased.  What do you think? Sound off on our twitter @SciSidequests!!

Why is the Sky Blue?

By Scott Mattison (@FoolsPizza)

Blue Sky

At some point, every parent is asked why the sky is blue. A good way to explain this to a five year old is to ask them what colors make up white light, in case you forgot its the rainbow. Remind them the colors of the rainbow (red, orange, yellow, green, blue, indigo, and violet). Then explain that the air we breathe actually changes the way light moves. This is because air is made up of molecules that the light hits and changes the light’s direction. Finally, you can simply explain that the inner part of the rainbow (blue, indigo, and violet) move through the air the best to reach our eyes, giving the sky its blue color.

For the kid that keeps asking, “why” you can give them the simple answer to this question: an effect known as Rayleigh Scattering caused by small molecules in the atmosphere is what gives the sky it’s blue color. Rayleigh scattering causes shorter wavelengths to be scattered a lot more (1/wavelength^4).  Remember the colors of the rainbow from longest wavelength to shortest wavelength are red, orange, yellow, green, blue, indigo, and violet. Blue being a shorter wavelength means blue light dominates the scattered light coming from the sky.

A tricky question a kid could ask is, “why the sky isn’t violet?” This is a great question. Violet is the shortest wavelength of light we can see, so if shorter wavelengths are preferentially scattered, why isn’t the sky violet? The answer to this question is actually really cool and makes light really fun to study!

To fully explain to your (hypothetical?) child why the sky isn’t violet, first you should talk a bit more about how light scatters. The two most common ways that light scatters are Mie Scattering and Rayleigh Scattering. Mie’s solution to the scattering of light allows us to model the movement of light as it interacts with particles, like dust and water, that are similar size or larger than the wavelength. With Mie scattering, light is mostly scattered along the direction it originally hit the particle, and the effect is not wavelength dependent.

MIE
Light undergoing Mie Scattering

Rayleigh scattering, as we have already mentioned, is what gives the sky its blue color. Rayleigh scattering occurs when light interacts with particles much smaller than the wavelength size. Light that undergoes Rayleigh scattering is equally scattered in every direction. Rayleigh scattering is exponentially stronger with shorter wavelengths, meaning short blue, indigo, violet end of the spectrum is much more strongly scattered than the red, yellow, green end of the spectrum.

Rayleigh
Light Undergoing Rayleigh Scattering

Now that your (again, hypothetical ) kid knows how light scatters, you can help them begin to build an understanding of why the sky is blue. Light that is Mie scattered will mostly continue moving in the direction it was moving. So if you let your kid look at the sun (a terrible idea), they will see the effects of Mie scattering (especially if there are clouds in the way). However, if you kid looks at the rest of the sky, light that has been Mie scattered is going to keep moving away from their eyes. So overhead, Rayleigh scattering is dominant, giving the sky its blue color.

Up to this point you have only really explained to your kid the short answer for why is the sky blue. The second part of this answer relies on a the second way that light can interact with matter, absorption. I have previously talked a little about the absorption of light when I tried to figure out how to attach a laser to a shark. Here though, I am going to focus on how our bodies use the absorption of light to help us perceive the world around us.

The eyes of most people detect light via rods and cones. Rods and cones absorb light and convert the energy absorbed into a signal sent to your brain. Rods are responsible for non-color specific and night vision, whereas cones provide you with your perception of color. Most people have 3 types of cones in their eyes, one for the detection of shorter wavelengths, violet to blue, one for the perception of longer wavelengths, orange and red, and one for the perception of the middle wavelengths, green and yellow.

Rods and Cones
The light absorbance of rods and cones. Image Source: Wikipedia

Now, what colors make up white light? There are two answers to this question the first is shown on the album cover to Pink Floyd’s dark side of the moon. As we pointed out at the start, white light is made up of all of the colors of the rainbow. The second answer to this question is more familiar to anyone who works with colors on a computer. We can simulate white light with simply an even combination of red, green, and blue. In fact, we can actually simulate most colors by manipulating combinations of red, green, and blue.

So now we can get back to the question at hand, why is the sky blue? While Rayleigh scattering does preferentially scatter violet light over blue light, our eyes are far more sensitive to blue light. Additionally, Rayleigh scattering is occurring in the sky for all wavelengths of visible light, shorter wavelengths are merely scattered more. In fact what we are seeing as the color blue is really our eyes average out all of the wavelengths present in the sky and creating the perception of blue light.

Now that your inquisitive (possibly hypothetical) child has likely completely lost interest you can explain that all color is merely how our eyes perceive the world. This is why individuals who are colorblind may not realize it until much later in life. Then you can go show them other cool optical illusions that are so good are fooling us.

Mitochondria: more essential than Midichlorians?

By Reed Stubbendieck (@bactereedia)

Midichlorians are a microscopic lifeform that resides within all living cells… And we are symbionts with them… Lifeforms living together for a mutual advantage. Without the midichlorians, life could not exist, and we would have no knowledge of the Force.

Qui-Gon Jinn, Star Wars Episode 1: The Phantom Menace

Note: this post contains a minor spoiler for Star Wars: Episode VIII – The Last Jedi

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Image Credit: Wookieepedia

In one conversation between Jedi Master Qui-Gon Jinn and Anakin Skywalker, the origin of the Force shifted from the mystical to the microbiological. And while I love all things microbiology, I can’t say that even a ten-year old Reed appreciated the introduction of midichlorians into the Star Wars canon (though let’s be fair, not many people did).

Qui-Gon Jinn says that life cannot exist without midichlorians and the Force is conducted through the midichlorians and refers to the midichlorians as microscopic lifeforms that live inside our cells. It’s well documented that Star Wars director George Lucas derived inspiration for midichlorians from an organelle that exists within most of our own cells called the mitochondria. 

Similarly to midichlorians, all human life is dependent upon mitochondria. However, while midichlorians connect living things to the Force, our mitochondria connect us to an even more powerful force: aerobic metabolism!

In today’s post, we will explore what would happen if a human being was suddenly cut off from the force of aerobic metabolism (much like how Luke cut himself off from the Force in The Last Jedi). More specifically, we will determine how long a human can survive if they were to suddenly lose all of their mitochondria.

mitoEM
Transmission electron micrograph of a mitochondrion. Image credit: G. Angus McQuibban

Before we begin, I will briefly describe the function of our mitochondria (pictured above), which are (in)famous for being “the powerhouse of the cell”. That is, most of our energy generation occurs due to biochemical reactions that take place within the mitochondria.

Learning about metabolism is one of the banes of introductory biochemistry courses, but for our purposes, we can represent the many enzyme-catalyzed reactions, substrates, cofactors into a single equation, where C6H12O6 is glucose (a sugar) that we consume and adenosine triphosphate (ATP) is the energy currency of our cells:

eq1

This process, which is called oxidative phosphorylation, absolutely requires our mitochondria to occur. Without mitochondria, our cells can metabolize glucose in an oxygen-independent process called anaerobic glycolysis. However, anaerobic glycolysis is much less efficient than oxidative phosphorylation and causes a buildup of lactic acid. Under conditions of oxygen deprivation (e.g., asphyxiation), our brains rapidly suffer damage due to a combination of lack of energy and acid buildup in brain tissue.

Similar to my first post, I will use back-of-the-envelope calculations to estimate how long a human will survive without their mitochondria. I will make the following two assumptions:

1) The first organ to suffer irreparable damage from complete loss of mitochondria is the brain.

2) Death will occur due to lack of energy, in the form of ATP molecules.

To determine how many long it would take for our brains to deplete their total ATP, we need to determine how much ATP our brains contain and the rate of ATP consumption. First, we will calculate the amount of ATP in our brains. A rat neuron contains 2.6 mM ATP, an average human cell has a volume of 4000 µm3, and the brain contains ~240 billion cells. Using these numbers we can estimate the ATP content in a human brain:

eq2

This number corresponds to ~1.4 grams of ATP contained in our brains. For comparison, a paperclip has a mass of ~1 gram.

Next, we need to determine how much ATP our brains generate. Under normal conditions, over the course of a single day, we produce ~60 kg of ATP! Using this rate, we can calculate how much ATP our bodies generate per second:

latex_2169373ff5f1f0b374f1a33ea30a1053

But, recall that if we suddenly lose all of our mitochondria, then we can only generate ATP from anaerobic glycolysis, which only yields 2 molecules of ATP for every molecule of glucose, which is 18× less efficient than oxidative phosphorylation:

eq4

Our brains use roughly 20-25% of the total oxygen that we consume, so one-quarter of the ATP that we produce occurs in our brains. With this, we can calculate how much ATP generation occurs per second in the brain:

eq5

Finally, we need to calculate how much ATP our brains use. The human brain consumes 80 µM of ATP per second and averages 1.5 liters in volume. Using simple multiplication, we calculate:

eq6

Now we have all the numbers to determine how long it takes for our brains to deplete their ATP after losing all our mitochondria. We know our brains contains 2500 µmol of ATP,  they produces 20 µmol of ATP per second, and consumes 120 µmol of ATP per second. We calculate:

eq7.png

 

eq8

Thus, it will take our brains less than a half-minute before they deplete their energy stores, which corresponds closely with clinically established 1 minute time frame before brain cells begin to die due to lack of oxygen.

Therefore, if you suddenly lost all of your mitochondria, your brain will begin to die 21 seconds before Qui-Gon Jinn can finish ruining the mystique of the Force (for reference, 46 total seconds)!

 

Look forward to an upcoming post about the origins of organelles including mitochondria, chloroplasts, and maybe even midichlorians.

 

An Introduction on the Mating System of Koopas

By Andrew Anderson (@AndersonEvolve)

As an evolutionary biologist, it’s often a fun exercise to look at fictional creatures and think about how they might have evolved or how patterns in nature might apply to them. Ever since he became a playable in character in Mario Kart for SNES, I have always jumped at the chance to play as the King of the Koopas, Bowser–yes, even in Smash Bros where he’s a lower tier fighter. Video games aside, the lore around Koopas is sparse (or least from my knowledge), which leads to some great biological questions about how they function and survive. In particular, how do they reproduce and what mating systems might they have? In this post, I’ll set up some of the species boundaries of Koopas and in successive posts I’ll try to tackle some of the more interesting thought experiments.

bowser

First, we need to establish what creatures are Koopas. The classic concept of species is the Biological Species Concept, the idea that if populations can interbreed and yield fertile offspring, they are the same species (e.g. horses and donkeys can make a mule, but the mule is sterile–thus horse and donkey are separate species). This is a useful start point as it might help us demarcate what are and aren’t Koopas. In order to test the Biological Species Concept we need to know if interbreeding occurs. This is a dark-corners-of-the-internet thing, so I’ll just assume if a romance is present between characters then the result of a pairing would be fertile offspring. So a quick look at some known pedigrees in the Mario world and it looks like Koopas are pretty consistent in their appearance. Bowser had his 7 children for the early games (later retconned to be his minions, but some guide books still state they are his children), and one other child, Bowser Jr., who appeared in Mario Sunshine. We also have Koops who is the son of Koopley, and Kolorado who had an unnamed father in Paper Mario. Clearly Koopas beget Koopas.

200px-Hammer_Bro-NSMBU

But what about other denizens of the Mushroom Kingdom? Hammer Bros, Lakitus, and Boom Boom also have turtle-like appearances, so we’ll assume there isn’t any cryptic speciation (i.e., two different species that look similar) going on. It is also stated that Koopas evolved from Shellcreepers on the Mario Wikia. Shellcreepers still occasionally appear and certainly Bowser is as old as Shellcreepers, so they cannot be the ancestor to all Koopas. To be more accurate (although one can only do so much in a video game universe), I’m going to say Shellcreepers share a lineage with the other Koopas but are the most ancestral in form. Yoshis are from Dinosaur Land, which Bowser invaded, so they are geographically separate from Koopas.  The only romantic entanglement we get from Yoshi is Birdo and neither are have the turtle-like appearance, so it seems unlikely Yoshi is a kind of Koopa. There is a strange thing to consider though; while not cannon, the Mario Bros live action movie suggests that most inhabitants are related despite their drastically different appearances (I would lose so much time nitpicking its evolution statements–so I’ll ignore them). It also shows Princess Daisy as being hatched from an egg–implying the human-like characters might be reptile-like as are the Koopas. We know Bowser is infatuated with Princess Peach, and his claim that Bowser Jr. was her son was believed, though not true. The fact that such a lie wasn’t immediately rejected suggests some plausibility. So it may be that the human-looking characters of the Mushroom Kingdom are also Koopas.

lakitu

We can already see an issue with the Biological Species Concept. Are the princesses and Toads actually Koopas? What about Mario and Luigi? They’re from a different land and stated to be human, but have romantic interests in the two princesses. Clearly defining species is an interesting challenge in evolutionary biology. There are many ways to define a species in biology, though Biological is often a good start point for determining speciation in most sexually reproducing species. Scientists are uncovering more and more that hybridizations occur across lineages that are distinct enough to be considered separate species without sterilizing the offspring. In fact, humans have interbred with Neanderthals in the past despite the two being considered separate species. Evidence of this lies in sections of human genomes where parts of the sequence more closely match Neanderthal than the more ancient African lineage.  Thus, those who can trace their ancestry to regions where Neanderthals co-occurred with humans have ~3-5% of their DNA inherited from Neanderthals. So even though it is hinted at the intermingling of the human-like members of Mushroom Kingdom and Koopas, it is still possible to consider them different species; therefore, given the drastically different morphologies and their reluctance to even cohabitate, I will treat the human-looking members of the Mushroom Kingdom as a separate species, but one capable of interbreeding with Koopas.

boomboom

Now that we have determined what is and isn’t a Koopa, we can now move into the behaviors and morphologies that are found within the species.  Stay tuned for the next sections of this blog which will discuss the mating system and brood-care strategies of Koopas…

Lunar Light as a Trigger for Werewolf Transformations

By Scott Mattison (@FoolsPizza)

Most people are familiar with the idea of a werewolf, a human with the ability to shapeshift into a wolf or humanoid wolf monster.There are many variations of the concept of a werewolf, but most versions center around the notion that the full moon acts as the catalyst for the transformation. Completely ignoring the fact that such a transformation would require a rapid reorganization of several body systems, the time has come to ask the hard question: Are there any unique properties of a full moon that could cause such a transformation?

Now, you may be thinking that werewolves are magic, and clearly there is no need for science to try to explain magic. However, as scientists, it is important to question the unknown and develop a deeper understanding of our world. While werewolves may not be real, it is still fun to think of the answers as a what if scenario. [As a side note, if there is an entire magical community running around like in the Harry Potter books, they are colossal jerks for not sharing all of the medical breakthroughs that magic would bring.]

Does the full moon possess any unique qualities that could trigger the transformation from human to wolf? In many descriptions of werewolves, lycanthropy is a curse passed down by the bite of another werewolf. This curse may be some form of virus, similar to rabies, but I will leave that discussion to those more suited towards it.

As a general note, some stories involving werewolves treat the transformation as a timed process that occurs with the cycle of the moon, regardless of the presence of moonlight. Timed processes such as this are called lunar rhythms. Lunar rhythms are really neat, but this blog post will focus more on the moon and moonlight itself.

Most stories of werewolves involve the transformation typically only occurs at night during a full moon. The fact that the transformation only occurs at night is very important as full moons are often visible in the daylight. In fact some months, the full moon occurs entirely during the day. This tells us one of two things 1) it is not the shape of the moon that is triggering the transformation or 2) bright sunlight acts as an inhibitor to the transformation process.

Furthermore, many accounts of the transformation describe the individual only changing after being bathed in moonlight, and not requiring the individual to look at the moon. This observation further supports the idea that the shape of the moon is not triggering the transformation process. Confirmation of the existence of a blind werewolf would be required to fully confirm this theory. However, finding such a specimen may prove challenging.

This leads us to the idea that moonlight is what acts as the primary catalyst for the transformation. It is very possible for a virus to introduce an optically sensitive component to cells of the body. In fact there is a whole field of science, known as optogenetics, which allows scientists to introduce light-based control of muscle and nervous cells through genetic engineering. In that case, what is special about the light of a full moon? Well, during a single lunar cycle, lunar brightness increases exponentially as the moon waxes and decreases exponentially as the moon wanes. This means that during a lunar cycle, the full moon is the brightest. 

There are two big issues with the hypothesis of lunar brightness. The biggest issue is that if the transformation is caused by a brightness threshold alone, then a werewolf would transform anytime they walked out into the sunlight, as the moon is simply reflecting the light of the sun. This actually relates back to one of our observations earlier, bright sunlight may act as an inhibitor to the werewolf transformation. This would mean our virus is introducing some form of optically sensitive molecule that is activated at a certain threshold of light, but deactivated in some way by bright sunlight.

Wolf
Sunlight blocks the transformation of a person into a werewolf.

This isn’t too far fetched as the sun is roughly 400,000 times brighter than the full moon. Alternatively, there could be some spectral shift of the light reflected by the moon relative to the sun that triggers the transformation. The moon isn’t a perfect reflector and does absorb some wavelengths more strongly than others. The reduction of one wavelength beneath a certain threshold may be the requirement for the transformation to occur instead.

The second biggest issue is that the brightness of the full moon varies between lunar cycles depending on the angle between the moon and the earth, the distance between the moon and the earth, and the presence of small particles in the atmosphere. Interestingly, these changes are noteworthy because they do actually coincide with certain descriptions of werewolves.

Some accounts of werewolves describe the potential for the change to occur on the days preceding and following a full moon. This could be due to the moon being closer to the earth (so that it takes up more of the sky) or at a point higher in the sky (so that it is traveling through less atmosphere). Furthermore, many accounts of werewolf encounters describe the transformation occurring as the moon appeared from behind the clouds. This is in agreement with the theory that a certain optical threshold must be reached to cause the werewolf transformation.

In conclusion, we propose that lycanthropy is caused by the introduction of an a molecule that responds to light into the host’s cells. This molecule is activated by light above a certain intensity threshold and inhibited by the presence of bright sunlight. Thus, if werewolves are real and follow the rules discussed above any individual who has been bitten by a werewolf need only to wear a thick layer of sunscreen on the nights leading up to and following the full moon to prevent their transformation.

Author’s Note:

Major Spoilers for “Harry Potter and the Prisoner of Azkaban” Follow so if you haven’t read a 19 year old book (or watched a nearly 14 year old movie) stop reading here

My wife and I had a long debate on whether or not the werewolves in the Harry Potter books follow lunar rhythms. Through most of the books it is implied the transformation occurs whether or not the individual is exposed to moonlight during a full moon, thus implying a lunar rhythm. However, in the third book Lupin doesn’t transform until the moon comes out from behind a cloud and bathes the party in moonlight; implying moonlight is the catalyst for the transformation. So either the cloud moment is just meant as dramatic flair and he would have transformed at that exact moment either way (which could is probably true, but annoyingly coincidental) or the cloud moment is the answer and Lupin should never transform if he simply locked himself in a basement or dungeon. Either way we were definitely overthinking the whole situation.