Tag Archives: Human

The Man Behind the Curtain Turns 1

The Man Behind the Curtain turns 1 today! In the past year, this blog has had over 4800 views from people in 104 nations. This surpassed what expectations I had, and I am looking forward to another good year.

The most popular posts this year were:

Dinosaurs are not Extinct

Hot or Not

Do genes skip generations?

Testing a Claim: Ceramic Knives

The least popular posts were:

Drug-Resistant Diseases

Skipping Generations Part 2

You’re Doing it Wrong, Part 2: Post Hoc Ergo Propter Hoc

A UFO (which was my first post)

And these are my personal favorite posts:

For All Mankind

Dinosaurs are not Extinct

10% of our Brains

The Evolution of Flight

Thanks for reading! I hope 2015 will be even better. (Tomorrow I will go through and fix all of the broken images. Sorry about that.)

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What Does It Mean To Be Supernatural?

Image from clipartpanda.com

Halloween is coming up, and popular culture is being filled its annual dose of references to the supernatural (including the recent season premier of the show Supernatural, which is probably not a coincidence). Ghosts, monsters, black magic, vampires, witches, and others all fall under this umbrella of “the supernatural.”

But what does it mean to be supernatural?

My dictionary defines “supernatural” as “(of a manifestation or event) attributed to some force beyond scientific understanding or the laws of nature.”

Being beyond scientific understanding is actually very mundane. Most of the way the brain works is beyond our current scientific understanding, but no serious researcher is throwing up his or her arms and declaring it supernatural. The relationship between mass and energy was beyond scientific understanding until Albert Einstein figured it out. The origin of mitochondria and chloroplasts were beyond scientific understanding until Lynn Margulis figured it out. Every issue of every scientific journal is filled with things that were beyond the understanding of science just a year or so prior. This is not what people mean when they say that something is supernatural. They mean the second thing — beyond the laws of nature. The word supernatural literally means “above nature,” or, more figuratively, outside or separate from nature.

But what is nature and what are its laws?

Consulting my dictionary once again, “nature” is defined as “the phenomena of the physical world collectively, including plants, animals, the landscape, and other features and products of the earth, as opposed to humans or human creations.” And once again, my dictionary fails to provide a completely cogent or useful definition. If humans and our creations are not natural, does that mean that the computer I’m writing on is supernatural? Again, no one would reasonably make this claim. The first part of this definition, “the phenomena of the physical world collectively,” is actually pretty good as it is. Nature, or the physical world, is made up of two things: matter and energy, which Einstein showed us are the same thing. Nature is everything that exists. It is all of the animals, plants, fungi, bacteria and all of the rest of life. It is all of the rocks and minerals and water and air. Even humans, which are animals, are part of nature. Everything beyond our planet is part of the natural world, as well. All of the undiscovered types and forms of matter and energy are part of nature. Every answer to an empirical question is part of nature, and it is the job of scientists to discover nature as it exists.

Are ghosts real? This is an empirical question because the answer is not subject to ideology or personal preference. It’s not possible for ghosts to be real for me but not real for someone else, any more than  the statement “the earth’s atmosphere is 78% nitrogen” can be real for me but not real for someone else. Correct answers to empirical questions are correct whether you like it or not. Likewise, either ghosts are real or they are not. If they are real, they are part of nature, and are therefore natural phenomenon. It may come as a surprise to people that, if ghosts are real, it will be scientists who discover them. This is true of everything else that is commonly labeled as “supernatural.” If everything that exists is part of nature, then what does that mean? If something is truly supernatural, it doesn’t exist.

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Sex With Aliens

Science fiction is full of humans interbreeding with intelligent aliens from all over the galaxy.

In the original Star Trek series, Captain Kirk mates with a wide variety of aliens, although he never fathers any children with them that we know of. Spock is half Human, half Vulcan. There are several characters in Star Trek: The Next Generation who are the result of alien-human mixing, as well. Worf is 100% Klingon, but his wife, K’Ehleyr, is half Klingon and half Human. Their son, Alexander, is therefore one quarter Human and three quarters Klingon. Deanna Troi is half Human, half Betazoid. The list goes on and is certainly not limited to Star Trek.

Star Trek’s Spock is half Human and half Vulcan. Image from wikipedia.org

I hope I’m not ruining anyone’s fantasy by pointing out up front that this is not even remotely plausible.

Imagine a human trying to produce offspring with an insect or a tree. Once you’ve stopped laughing, imagine trying to do the same with a bacterium, which is as distantly related from humans as you can get on Earth. Now consider that reproducing with a life form from another planet is far less likely to work out than trying to reproduce with a bacterium from Earth.

For two different species to be reproductively compatible, they cannot have very much evolutionary distance between them. Zebras (Equus zebra), horses (Equus ferus) and donkeys (Equus africanus) can all reproduce with one another. Lions (Panthera leo) and tigers (Panthera tigris) can sometimes produce offspring. The common chimpanzee (Pan troglodytes) and the bonobo (Pan paniscus) can produce offspring. (As is typical of cross-species hybrids, the offspring of these pairs are not fertile themselves.) I hope you noticed a commonality among all of these matches: they are all in the same genus. Lions and tigers are both in the same genus (Panthera) and they can sometimes reproduce together, but neither the lion nor the tiger can reproduce with a chimpanzee or a zebra because they are not closely related. This is not a hard and fast rule, though. Many species that are in the same genus cannot reproduce together, and occasionally species that are not in the same genus can reproduce together.

The liger is a hybrid between a tiger (Panthera tigris) and a lion (Panthera leo). Image from wikipedia.org

Life on Earth began somewhere between 3 and 4 billion years ago. Since then, life has evolved and diversified to produce the wide range of species that we see today. Another planet with life would have had its own origin and its own evolution to produce whatever diversity that planet has in whatever amount of time it took. An intelligent species on another planet would be unable to reproduce with most of the other species on its planet, just as most species on Earth cannot reproduce with one another. Humans are not able to reproduce with any other species on our planet. Even chimpanzees and bonobos, which are our closest evolutionary relatives, cannot produce offspring with humans (though it is not for a lack of trying). We share almost 99% of our DNA with chimpanzees, and are physically capable of mating, and yet we cannot reproduce with them. So what are the chances of being able to reproduce with a species that evolved from a completely separate origin of life? In this particular case, the likelihood is roughly equal to the percent of our DNA that we share: 0%.

 

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10% Of Our Brains?

There is a new movie coming out later this month called “Lucy.” (See the trailer here.) The premise of this movie is that humans only use 10% of our brains, and Scarlett Johansson  gets superpowers by using more than 10% of hers. This idea that we only use 10% of our brains, but would be better if we used more, is a very persistent myth in our society.

Disclaimer: My point here is not to rain on anyone’s parade. I love science fiction movies, and if Luc Besson’s record is any indication, this one will probably be good. (Personal note: Luc Besson wrote and directed my favorite movie.) Even though I am a scientist, I am usually willing to suspend my disbelief for whatever premise the movie asks me to accept. I am not trying to convince anyone that they shouldn’t watch this movie or that it will suck because it gets some facts wrong. The release of this movie is just a convenient opportunity to talk about an oddly persistent myth.

Now back to the show…

My first exposure to this myth was probably as a child when I read the book My Teacher Fried My Brain — the second book in the My Teacher Is An Alien series. In this book, the school bully has his brain zapped by an alien device which makes him much smarter and a much more pleasant person. I can remember speculating later that very smart people like Albert Einstein probably used more like 50% of their brains.

But none of this is true. There have been several takedowns of the 10-percent-of-our-brains myth from a neuroscience perspective by people who are more qualified than I to discuss neuroscience. I am much more qualified to discuss this from an evolutionary angle.

Evolution is incremental. Traits evolve slowly over time, with each successive version of the trait being slightly better than the last. The brains of modern humans have a volume somewhere in the area of 1200 cubic centimeters (cc). Chimpanzee brains have less than a third of this volume. We evolved from an ape that was not exactly a chimpanzee, but we can use the chimp brain size as a point of comparison. Since our evolutionary divergence from our chimpanzee-like ancestors, our brains have tripled in size. This means that, during our evolution, individuals with 450cc brains survived and reproduced better than individuals with 430cc brains, and individuals with 500cc brains survived and reproduced better than individuals with 450cc brains. Our brains eventually grew to what they are now because the modern brain allowed individuals to survive and reproduce better than individuals that had anything less than a modern brain.

Human brain (top) compared to chimpanzee brain (bottom). Image from scientificamerican.com

The modern human brain is astonishingly expensive to build and maintain from a caloric standpoint. A typical adult male at rest requires 1800 Calories per day to function. That is, a man lying motionless but awake for 24 hours will burn 1800 calories just to maintain his body. This 1800 Calories is his “metabolic budget.” The metabolic budget is just the cost of every process within the body added up. Keeping the heart beating and the lungs breathing requires some of these calories. Replacing old, worn-out cells requires some more of these calories. The average adult male brain requires 414 of those Calories, which accounts for 23% of the total resting budget. Typical adult females require fewer Calories to function (1480) than adult males. The female brain requires about the same number of Calories as the male brain (400), but accounts for a slightly larger percent of the resting metabolic budget (27%).

Malcom Holliday (1986) studied the energetic cost of the brain at different stages of life. (The data above is his.) The brain is relatively more expensive at younger ages because the brain is growing very fast and because the brain accounts for a larger portion of the body’s overall mass.

Malcom Holliday (1986) studied the energetic cost of the brain at different stages of life. (The data above is his.) The brain is relatively more expensive at younger ages because the brain is growing very fast and because the brain accounts for a larger portion of the body’s overall mass.

Evolution is not wasteful. Acquiring enough energetic resources to survive was a big problem for our ancestors. Building a smaller brain would be less expensive. If the expense of building a bigger brain was not offset by the advantage it gives, it would never have evolved in the future. If humans suddenly found ourselves in an environment where our big brains were no longer an advantage for us, our brains would subsequently evolve to be smaller. (Remember that evolution does not always make things bigger, better and more complex.)

If the brain was larger (and therefore more energetically expensive) than it needed to be, individuals with a smaller brain would be able to spend that additional energy on other important things. They could spend it acquiring resources to support more offspring. They could spend it on growing bigger muscles and repairing more damage. Or they just wouldn’t require as much energy to survive and it would be harder to starve to death. This is to say that a brain that wastes 90% of its potential could not possibly evolve. Compare this to a centipede that only used 10 of its 100 legs or a cheetah that had the anatomy and physiology to run 70 miles per hour but never ran faster than 7mph. Evolution would not produce these traits, either.

In summary: a brain that leaves 90% of its potential untapped would not evolve. But don’t let this fact stop you from making good movies that use this as a premise. Luc Besson doesn’t tell me how to do my job, so I won’t tell him how to do his.

Have a topic you want me to cover? Let me know in the comments or on twitter @CGEppig. Follow me on Facebook.