Category Archives: Uncategorized

What’s in a species?

Take two biologists, sit them down, give them a few beers each, and then ask them to define the word “species”. Chances are you’re in for a colorful discussion. “Species” is one of those concepts that made perfect sense in high school, got fuzzy in college, and is something biology graduate students like to debate on the weekends.

Person A: It’s easy, right? If two organisms can create viable offspring, they are part of the same species.

Person B: Well, what about hybrids? You know, like when a horse and a donkey (clearly different species) mate and produce viable mules.

Person A: Well, mules are (usually) sterile, so that doesn’t count.

Person B: Ok, how about the viable and fertile offspring produced when Canids mate, like dogs and wolves or coyotes and wolves?

Person A: But those are recently diverged groups, I’d argue that they were actually subspecies of the same species (since they can produce viable fertile offspring, they’d be a subspecies by definition).

Person B: Alright Linnaeus, now you’re rewriting taxonomy. So you’re saying that as long as two organisms can produce fertile offspring, they’re members of the same species?

Person A: Right, but we can still define them into separate sub-species.

Person B: What about when organisms from two different genera produce viable offspring, like Fatshedera lizei ? 

Person A: Are the offspring fertile?

Person B: Well their are some reports that…

Person A: That’s a plant anyway, the rules are different for plants.

Person B: Wait, what are the rules for “species” in asexual organisms, especially when genetic code can be passed on by horizontal gene transfer? And what about cancer as a speciation event? You know, the idea that a tumor has a separate genome from its host so it should be thought of as a different species.

Person A: No way, man. Cancers are formed from and completely dependent on their host. It’s just an extension of a single organism.

Person B: Not necessarily! The Tasmanian Devil facial tumors are spread between hosts by contact. Why shouldn’t we consider those cells a unique pathogen, no different than a virus spread between hosts? And how should we classify that ‘organism’?

Person A: Are viruses even considered alive?

Person A+B: …I think I need another drink.

Yes, I’ve had similar conversations over the years as a biology graduate student. I was reminded of the species debate after reading about the “out of Africa” concept and human speciation, and whether or not we interbred with members of other hominid groups (and, what that means for the definition of our species).

1.1 Billion

That’s the number of heartbeats in every animal’s lifetime*. Don’t believe me?

Let’s consider an extreme comparison. A mouse can live for 3 years, and has a heartbeat of about 670 beats per minute. There are 525600 minutes in a year (365 days/year * 24 hours/day * 60 minutes/hour). So, that’s 3 years/lifetime *525600 minutes per year * 670 beats/minute ≈ 1.1 billion beats/lifetime. What about an elephant? They can live up to 70 years and have a heartbeat of about 30 beats/minute. 70 years/lifetime * 525600 minutes/year * 30 beats/minute ≈ 1.1 billion beats/lifetime. Woah… what?!

Ok, ok… you probably noticed that those “equals” signs are actually squiggly “approximately” signs, and if you did the math (you should!) you would see that they are both a little off from exactly 1.1 billion. But still, they are damn close. What gives? Why would the number of heartbeats be an invariant property of the animal kingdom? Let’s dive a little deeper.

The answer lies in allometric scaling, or how different properties of life scale with the body mass of organisms. It turns out that the power (energy per time, metabolism) required to support a given unit of mass of an organism scales with the mass of that organism to the (-1/4) power- meaning that smaller organisms use energy at a faster rate per unit mass than larger organisms. Other rates, such as breathing rate and heartbeat rate, also scale with bodymass^(-1/4). Lifespan, on the other hand, has been shown to scale with bodymass^(1/4). If you want to find how the lifetime total beats scale, you can multiply those two together (beats/time * time = beats). Bodymass^(-1/4) * Bodymass^(1/4) = Bodymass^0, which is always 1, meaning that the total beats is invariant of bodymass! More on allometry and metabolism in later posts. And maybe I’ll learn how to show equations in wordpress someday.

This paper (which probably takes into account more than the 2 points I used above) cites the total number of heartbeats in an animals lifetime as 1.5 billion.

Now, given this number, can we backtrack and use the relationship to see how long humans are predicted to live? Given a certain heart-rate, how long would it take us to use up our 1.5 billion?


R code:
curve(1.5e9/(x*525600), xlim=c(40,100), lwd=5,
ylab=”Lifetime (years)”, xlab=”beats/minute”);
abline(v=60, col=”red”);abline(v=70, col=”red”)

If an animal beats its heart between 60 and 70 times a minute, it would use up its 1.5 billion beats in around 40-45 years. Is this a ballpark estimate of a human’s lifetime in the wild? (Aside: if you take the 1.1 billion heart beats derived from mice and elephants and assume a heart-rate of 70 beats per minute for humans you get 29.9 years!)

Now, don’t worry. Humans have found amazing ways to increase their lifespan, and it’s not like everyone has a set number of heart beats to get through before it’s all over. This is just an interesting result of looking at metabolism and ecology – and what’s even more interesting is looking at the animals that stray from the predictions.

*That’s about the predicted number of heartbeats in an average organism’s lifetime

Cool weather

The recent cold snap across the U.S. dusted off some neurons that hadn’t been used since Earth Science- and in the process I made a pretty cool (lol) connection with some images of Saturn recently released from NASA. The Earth has a vortex of cold air spinning around its North Pole, and in early January this vortex branched out and dropped a blanket of cold air onto the Americas.

Image Image

As you can tell from the above images, our polar vortex isn’t especially consistent or symmetrical in shape. The same can not be said for Saturn’s polar vortex


Credit: NASA/JPL-Caltech/SSI/Hampton University

The beautiful series of images above was taken from the Cassini spacecraft. “The hexagon”, as it’s known, has a hurricane at its center with cloud speeds of 330 miles per hour.


Credit: NASA/JPL-Caltech/SSI

It’s awesome to see well-documented phenomena on Earth taken to their extreme on foreign planets. Hopefully we’ll see more as we continue to explore the worlds in our solar system and beyond.

Check out more stunning images of the hexagon here.

Cuban Treefrog (Osteopilus septentrionalis)


I am pretty sure this is a Cuban Treefrog, although please tell me if I’m wrong!


I let it go outside (sorry native frogs :-/). Anyway, it was definitely a neat surprise to find inside! That is, if you aren’t native to Florida yourself.


Carolina Wolf Spider

Carolina Wolf Spider

Hogna carolinensis, found in my apartment, Gainesville, FL.

Our message to the cosmos.

In 1977 we flung an atomic powered robot into space. Voyager 1’s primary mission was to beam data back to Earth as it cruised through the outer solar system. One of the most famous bits of data sent back is this image of Earth captured as Voyager looked back towards its home planet in 1990 (Awesome commentary on this image and our planet/species by Carl Sagan here)


The Pale Blue Dot image taken 6 billion km from Earth in 1990.


Voyager, continuing with the momentum gained from its primary mission, has recently left our solar system and started its secondary mission of being a message in a bottle from our species to the cosmos. The message is stored on an easy-to-read golden record, and contains greetings in different languages, sounds from Earth, brainwaves of a human, and images from around the planet.


The Golden Record.

The cover of the record contains an easy to read explanation on how to retrieve the data– defining time units in the universal constant of the fundamental transition of the hydrogen atom. The location of our solar system is also printed on the cover, in relation to 14 pulsars with unique periods.

Check out President Jimmy Carter’s message to who/whatever finds Voyager- “This is a present from a small distant world, a token of our sounds, our science, our images, our music, our thoughts, and our feelings. We are attempting to survive our time so we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination, and our good will in a vast and awesome universe.”

It’s awesome to know that there is a time capsule of our species and planet floating through interstellar space- likely to last billions of years in the cold reaches between the stars. I’d like the think that one day something pics it up and gets to hear Johnny B. Goode by Chuck Berry.


Hello, world.

If I had a nickle nickel dollar for every time someone told me to start a blog I would have, like, enough money to buy a domain for a blog. Well, here we are. I’m about to couple my need to share fun and interesting links and thoughts on our universe with my need to become a better and more confident science writer. I hope you bear with me, kindle discussion, tell me when you disagree, ask questions, offer suggestions for improvement, and learn something. And, for those who have been encouraging me, thank you.

By the way, for those not privy to programming, the title of this post is kind of a joke. Somebody out there smiled, right?