This is the first story in a four-part, weekly series on taxonomy and speciation. It's meant to help you as you participate in Armchair Taxonomist — a challenge from the Encyclopedia of Life to bring scientific descriptions of animals, plants, and other living things out from behind paywalls and onto the Internet. Participants can earn cool prizes, so be sure to check it out!

If you aren't totally clear on what constitutes a species, or how scientists draw the line between one species and another, don't feel bad.

Quite frankly, the scientists are a little shaky on this stuff, as well.

That's because species aren't easily defined, and there's a lot of debate over whether an individual animal, plant, fungus, or bacterium belongs in one species group or another. In fact, if you want to know what a species is, it's best to not bother trying to grope for a strict definition, taxonomists told me. Instead, every species is really a hypothesis. "It's a testable conjecture," said Mark Siddall, curator of the phylums Annelida and Protozoa at the American Museum of Natural History. "It's a hypothesis about common ancestry, and the recency of that common ancestry."

But that hasn't always been the case.

A lot of the language we use to talk about taxonomy today was handed down from the work of 18th-century European scientists. These men, including Carl Linneaus (who is called the father of taxonomy), were working off of a very different understanding of the world. To them, taxonomy was mostly about organizing the natural world that had been given to humanity, in its current form, by God.

From their perspective, the deity created things separately, and those things had remained separate. So all you had to do was look around and spot the obvious difference between one group of things and another. Leeches were very clearly different from lions. Plants with three leaves and yellow flowers could be separated from plants with four leaves and red flowers. It was a human responsibility, as God's bookkeepers, to assign names to those distinct groups.

The trouble is, that view has some pretty obvious flaws, right off the bat. Yes, there are clear delineations between a leech and a lion. But what about between leeches?

This is a leech.

And so is this.

Leeches come in a rainbow of different colors, shapes, and sizes. They live in different places. They eat different things. (In fact, there are a surprising number of leeches that do not want to suck your blood.) And how do you draw the line between a leech and a worm? It's not always an open-and-shut case.

Yup. Still totally a leech.

Today, scientists recognize roughly 700 different species of leeches, Siddall said. We also know that leeches, as a whole, are themselves a sub-class. Those 700 leech species are all types of segmented worm.

All of this flows out of our understanding of evolution. When we say those 700 species are all types of leech, we're saying that we think they share a common ancestor. When we say that leeches are a type of worm, what we're really saying is that leeches and worms share a common ancestor — and that that ancestor is not as recent as the one shared by all the different leeches.

Those are hypotheses, and they could be wrong. Because evolution is an ongoing process, the relationships those hypotheses describe could also change.

"In some ways we're still at a very early stage in taxonomy, despite doing this for 250 years," Ellinor Michel said. She's a researcher with London's Natural History Museum and an expert on mollusks. Everybody agrees that nature is clustered in units, she said, but that's about where the agreement ends. "Some people think that if you knuckle down, we'll find the right clusters to put everything in. Others say that 'what is a species' is driven by the perspectives of individual scientists and the changing needs and desires of society.".

"But wait!" you may be thinking. "Isn't this also about sex?"

Pictured: A liger.

Back in junior high and high school, sex was probably a big part of what you learned about species. In order for two living things to be part of the same species they have to be able to get it on, and make a baby — and that baby has to be capable of becoming a parent.

That's not a bad rule of thumb to start off with, Michel and Siddall say. In fact, some of the earliest work Ellinor Michel did as a taxonomist involved taking many different snails from the bottom of Tanzania's Lake Tanganyika and trying to see which ones would mate together.

"I tried to set up these little breeding experiments. I had a bench covered with little dishes of snails at the University of Burundi," she said. "But we didn't know what to do to make the snails happy enough to mate. It was a complete exercise in futility."

Today, she says, scientists agree that ability to interbreed doesn't count if you have to force it. There are examples of captive lions and tigers having baby ligers (or tigons, depending on which species is the mother and which is the father). Ligers can even produce offspring of their own. But we don't say that lions and tigers are the same species, partly because there aren't any well-documented cases of the two animals reproducing together in the wild, without urging from humans.

The process of evolution also helps to make the sexual definition of species problematic. Living things adapt to their habitats. When the habitat changes, you start to see behavioral and biological changes that can end up leading to the creation of a whole new species, somewhere down the road.

Larus gulls are one of the big examples of this. Larus is a genus, comprised of several different species, some of which live in a circle around the North Pole. One species of Larus gull lives in Norway. Another lives in Russia. Others live in Siberia, Alaska, Northern Canada, and England. The Larus gulls that live in England can interbreed with the Larus gulls that live in Canada. But they can't interbreed with the ones from Norway. As the Larus gulls' common ancestor circumnavigated the pole, its descendants ended up more and more different from the original population that had been left behind. By the time Larus gulls met Larus gulls again, they were so different as to be unable (or unwilling) to produce chicks together. But scientists consider every step in that process to be a different species — not just the gulls at either end of the broken ring.

All of this is really about species as groups — hypotheses that mark the temporary boundaries between one group and another and help us understand how different groups are related.

But species are also individuals. Very specific individuals, in fact. Next week, I'll take you behind-the-scenes at the American Museum of Natural History in New York to meet a type specimen — an individual animal by which all other animals in the species are judged.

Scientific American has an awesome contest going on right now. They're challenging you to make a video explaining some part, process, or system in the human body using eight objects: Yourself, a writing surface, a writing implement, rubber bands, paper clips, string, cups , and balls. You have to use all eight items. You can't use anything else.

You can read the full instructions and rules online. And check out the sample video, made by Scientific American interns Isha Soni and Mollie Bloudoff-Indelicato.

Bonus: The first 100 qualified entries all get a free digital subscription to Sci Am.

Via Bora Zivkovik

The more accurate version of this question would really be something like, "Why do some trees fall over in a storm while others stay standing?" The answer is more complex than a simple distinction between old, rotted, and weak vs. young, healthy, and strong. Instead, writes Mary Knudson at Scientific American blogs, trees fall because of their size, their species, and even the history of the human communities around them.

“Trees most at risk are those whose environment has recently changed (say in the last 5 – 10 years),” Smith says. When trees that were living in the midst of a forest lose the protection of a rim of trees and become stand-alones in new housing lots or become the edge trees of the forest, they are made more vulnerable to strong weather elements such as wind.

They also lose the physical protection of surrounding trees that had kept them from bending very far and breaking. Land clearing may wound a tree’s trunk or roots, “providing an opportunity for infection by wood decay fungi. Decay usually proceeds slowly, but can be significant 5-10 years after basal or root injury.” What humans do to the ground around trees — compacting soil, changing gradation and drainage “can kill roots and increase infection,” Smith warns.

Read the full piece at Scientific American Blogs

Paige the border collie can load the washing machine, pick up trash, and make toaster waffles (although you probably don't want to eat them afterwards).

And, with the help of her colleague Dexter — and their owner/trainer, who is also a chemist — Paige can even teach chemistry.

Here, Paige and Dexter serve as models for a discussion about chemical bonds — the forces that attract one atom to another and form the basis of all the chemicals that make up our world.

Via Matthew Hartings

For the next 60 years or so—basically, until everyone roughly my age has died off—former Alaskan senator Ted Stevens will be widely remembered (and mocked) for once describing the Internet as "a series of tubes".

But here's the thing. It's easy to make fun of Ted Stevens. It's harder (much harder) to explain quickly and at a relatively simple level—for lay people with no tech background—what actually happens when they call up a web page.

That's why Greg Boustead and the nice folks at the World Science Festival put together this short video, explaining the basics of the Internet, specifically the basics of packet switching. The video should help the average person understand the Internet just a little better and it has been run by several experts for accuracy, Boustead says.

I have to admit that when I had to screen it for "father of the Internet" Vint Cerf, who invented this process, I was more than a little nervous, certain he would pick it apart. When he replied with "This is so good - can I please use it to explain the concept of packets at public lectures," needless to say, I was over the moon.

So, the Internet. It's not a big truck. It's not a series of tubes. It's more like a bus full of tourists.

Video Link

Genius science writer Ed Yong used to work for a cancer charity, so he's seen how the cancer research sausages get made. In a new post at Not Exactly Rocket Science, Ed takes you on a brief tour of the factory, explaining why even good data doesn't necessarily mean what you think it means.

The post is based around a new study that says 16.1% of all cancers worldwide are caused by infections. This statistic is talking about stuff like HPV—viruses and other infections that can prompt mutations in the cells they infect. Sometimes, those mutations propagate and become a tumor.

That statistic tells us that infections play a role in more cancers than most laypeople probably think, Ed says. It gives us an idea of the scale of the problem. But you have to be careful not to read too much into that 16.1%.

The latest paper tells us that 16.1% of cancers are attributable to infections. In 2006, a similar analysis concluded that 17.8% of cancers are attributable to infections. And in 1997, yet another study put the figure at 15.6%. If you didn’t know how the numbers were derived, you might think: Aha! A trend! The number of infection-related cancers was on the rise but then it went down again.

That’s wrong. All these studies relied on slightly different methods and different sets of data. The fact that the numbers vary tells us nothing about whether the problem of infection-related cancers has got ‘better’ or ‘worse’. (In this case, the estimates are actually pretty close, which is reassuring. I have seen ones that vary more wildly. Try looking for the number of cancers caused by alcohol or poor diets, if you want some examples).

And that's only one of the complications involved in understanding cancer statistics. You really should read Ed's entire post. After you do, a lot of apparent inconsistencies in cancer data will make a lot more sense to you. For instance: What about the cancers caused by radiation exposure?

I ran into some of these problems while researching Before the Lights Go Out, my book about electricity and the future of energy. The topic meant I had to spend some time dealing with the risks posed by nuclear energy. Specifically, people want to know what happens to the local population when a nuclear power plant melts down. How many people die? The problem: There's more than one legitimate answer to that question.

Take Chernobyl. There is not one, definitive number I can give you for how many people died because of the accident at the Chernobyl nuclear power plant. There've been, if I'm counting correctly, six different papers estimating how many people the radiation released during the accident will eventually kill. The various estimations range from 4000 to almost a million. But beyond checking each other's methodology—and there are some serious problems with the methodology used by the paper that estimated the highest death toll—it's really hard to say who is right and who is wrong.

If you read Ed's post, you'll get two good clues as to why that is:
First, statistics that show you how many cancer deaths were caused by x factor aren't produced by counting the numbers of dead cancer patients. Those statistics are based on data, assumptions, and computer models. Use different data sets, different models, or different assumptions and you will get different numbers.
Second, cancer isn't like a collapsing roof. If a beam falls on someone's head you can look at the autopsy and say, "This death was caused by this piece of wood." You don't have to take into account the hundreds of times that person might have bonked their head on a doorway or cabinet over the course of their life. It was clearly the beam that did them in. But there's usually more than one reason people get cancer. In fact, a certain percentage of the population will get cancer simply as a side effect of being alive. Add into that all the other risk factors that most of us are exposed to over the course of our lives and it becomes extremely difficult to tease apart a real, honest-to-god answer to the question, "What caused this specific person's specific cancer?"

Read Ed Yong's full post at Not Exactly Rocket Science