Huge data set.

The debate about the origin of modern humans has been lively. Genetic studies from around the world have consistently found evidence of a single African ancestor. However, analyzing skull dimensions provided mixed results, with some studies arguing for a single origin and others supporting multiple origins of modern humans. So which one is it?

The debate can finally be put to rest. A new [review=http://www.nature.com/nature/journal/v448/n7151/abs/nature05951.html]paper[/review] looked at a large database of skull measurements from around the world and also looked at large genetic databases of samples collected from around the world. The results are very clear; quoting the abstract:

We find evidence for an African origin, placed somewhere in the central/southern part of the continent, which harbours the highest intra-population diversity in phenotypic measurements. We failed to find evidence for a second origin, and we confirm these results on a large genetic data set.

The technical result is this: genetic diversity is mirrored by phenotypic variability. Let’s try to explain this in simpler terms. Genetic diversity of a species is a measure of how similar or different the genetic makeup of its individuals are. An example of a species that has high genetic diversity is any wild animal population that’s not about to go extinct, like lions or monkeys, or zebras. The diversity is good because as the individual mate, the offspring will have random combinations of genes - the more diverse the genes are, the more random the combinations. This genetic randomness is very important, and is the subject of another post.

If a population loses members, say through an earthquake or over-hunting by humans or a disease, then the genetic variation decreases significantly. This is because you lose potential combinations of genes. The same effects can happen in artificial in-breeding. The net effect is that the genetic makeup of individuals in a population will start becoming more and more similar, a fact we can trace using advanced genetic analysis. This is one side of the paper.

The other side of the paper is phenotypic variation. A phenotype is the observed effect of a genetic makeup. An example: being tall (i.e., a phenotype of height) is the effect of having a certain set of genes (the genetic makeup, also called the genotype). You can guess that what we observe in the phenotype side should have a basis in the genetic side.

This is where the today’s paper comes in. All genetic studies said one thing, namely that modern humans started in Africa and spread out to the rest of world. However, phenotype studies gave mixed results, suggesting multiple human origins. Today’s paper fixes the phenotype observations: by looking at a huge data set, the researchers found that the phenotype changes (the skull measurements) mirrored the genetic changes. This nicely fixes the errors in the previous data.

It gets better: The farther away the samples were from the original starting point, the less genetically diverse and phenotypically variable they were. Reversing the argument, the samples with the highest genetic diversity and the highest phenotypic variation are the earliest (most historic) samples. Nicely, these diverse samples all came from somewhere in the central/southern part of Africa. As researcher Dr Francois Balloux explains, "To test the alternative theory for the origin of modern humans we tried to find an additional, non-African origin. We found this just did not work. Our findings show that humans originated in a single area in Sub-Saharan Africa."

And that’s how we know that modern humanity started in Africa. I know this post is a bit more technical than what I usually blog about, but it had to be done. Any questions please ask in the comments!

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Rejoice!

The world is buzzing with the news that European Space Agency (ESA) scientists have found water on a planet outside the solar system.

The planet, affectionately called HD 189733b, was discovered in 2005 at 63 light-years away and is classified as a ‘hot Jupiter’. Such planets are large and have extensive atmospheres because heat from the nearby star gives them energy to expand. Indeed, HD 189733b is 1.15 times the mass of Jupiter and its diameter is 1.25 times that of Jupiter. It is a mere 4.5 million km from its star; Earth is 150 million km from the Sun and Mercury, the innermost planet, is 70 million km away. Because of its orbit, one hemisphere of HD 189733b constantly faces the star, heating the planet only on one side to reach over 700 degrees C, or higher.

So just how do we figure out there is water in the atmosphere? It’s quite simple actually. As the planet moves around its sun, it hides parts of it from us (much like a lunar eclipse, but hiding a much smaller area). This means that the planet and its atmosphere are between it sun and our telescopes. We can measure what kind of light comes through from the planet’s sun, through the planet’s atmosphere, and onto Earth. How the light behaves through the atmosphere tells us a lot about its composition. What the ESA found is one infra-red band of light changed in a way that can only be explained by the presence of water.

The research is published in [review=http://www.nature.com/nature/journal/v448/n7150/abs/nature06002.html]Nature[/review].

Image credit: ESA - C.Carreau

As if yesterday’s magnets story was not enough, today we find that domestic chickens follow the Earth’s magnetic field, much like many other bird species.

The story starts around 40 years ago when Prof. Dr. Wolfgang Wiltschko proved that migrating robins use the Earth’s magnetic field to direct themselves during migration. Their magnetic sensor showed them the course of the field lines of the Earth’s magnetic field, helping them decipher which direction is the pole and which direction is the equator. Since then, a compass of this kind has been found in more than 20 species of birds, the majority of them being those songbirds that undertake annual migration, and now chickens join the roost group.

To show this, newly hatched chicks were imprinted on a red ball which they from then on regarded as their ‘mother’ (I know it sounds cruel but it’s not that bad, really). The researchers then hid the ball behind one of four screens, and taught the chickens by intensive training that the mother was always behind the screen that was in the northerly direction. To confuse the chickens, the researchers then set up an artificial magnetic field in an easterly direction (so East became the new North) and the chickens did actually seek their mother behind the screen that lay to the East. Finally, if the researchers used an oscillating magnetic field (i.e., one that comes and goes instead of staying steady), the chickens lose their orientation.

Why is this interesting? There are two key questions. Firstly, when did this evolve? Given the diversity of birds that have been shown to possess magnetic field orientation, the avian magnetic compass may have evolved in the common ancestor of all present-day birds to facilitate orientation within the home range. And since birds are really flying dinosaurs (yes, birds are direct descendants of dinosaurs!), it would be very interesting to figure out just how old this common ancestor is.

The second question is how do birds detect the magnetic field? In the beaks of chickens, iron-rich structures have been found, making them very likely candidates. However, the researchers showed that this area was most likely not involved in magentic orientation. This means that we still have work to do to find out what mechanism is used to detect magnetic fields.

The [review=http://jeb.biologists.org/cgi/content/full/210/13/2300]full paper[/review] is available freely, so go have a read. And if you get lost in all the science, it’s OK to joke about headless chickens… just this once

[tags]magentic field, chickens[/tags]

Superparamagnetic Colloidal Photonic Crystals… apparently.

From the Department of the Very Cool: scientists were able to change the color of the iron oxide solutions simply by changing the strength of the magnetic fields the solutions are in. The analogy is like tuning a TV (the old CRT tube TVs, not the new flatscreen ones). The researchers [review=http://www3.interscience.wiley.com/cgi-bin/abstract/114286507/ABSTRACT]studied[/review] very small particles (nanoparticles) of iron oxide suspended in water, much like milk or paint are both suspensions of substances in water.

When the strength of the magnetic field is changed, it alters the arrangement of the spherical iron oxide particles in solution, making them move closer or farther away from each other. This changes how light falling on the particles passes through or is deflected by the solution which gives color. Because they affect light they are called photonic crystals.

The new technology can be used to make an inexpensive color displays by forming millions of small pixels using the photonic crystals. A different color for each pixel can be assigned using a magnetic field.

[tags]superparamagnetic, colloidal, photonic, crystals, iron oxide[/tags]

To help blogSci and other science bloggers interact better with Postgenomic, I wrote a Wordpress plugin, called EasyPG, to quickly add the correct HTML markup used by Postgenomic.

Full details and download at the EasyPG home page. Enjoy!

[tags]science blogging, wordpress, easypg[/tags]

• Can you answer these science questions? They’re really basic, you know.
• Something hurting? Try Mayo Clinic’s online Symptom Checker. Essentially a questionnaire, it has a database of the most common illnesses and associated symptoms. By matching your description of the symptoms to its data, it displays a list of the most common causes of these symptoms. Of course, this does not sub for going to a doctor. Let me repeat: if you’re hurting, go to a doctor.
• A very useful resource: the online General Chemistry Glossary is exactly what it says it is. Never again be lost by the meaning of ‘zero point energy’.
• We’ve talked about Pi before, but how do we calculate it to millions of digits accuracy? We use a formula, like Ramanujan’s formula.

How human eyes track motion.

How do the eyes and brain work together to track a moving object? This is a key question in sports (and life in general), and lies at the heart of human motor control. Typically, when a person sees a moving object, the eyes quickly move to ‘lock-in’ on the object; this movement is called a saccade. After the eyes lock, the eyes smoothly track the object, with eye movement tracking the object relatively easily and without any sudden movements. Why this enhancement of tracking happens has so far been unknown.

A new paper sheds some very interesting light at this problem. The results suggest that there are two mechanism at work:

• low-level motion perception that helps the eyes catch up to the moving object more quickly
• high-level motion perception that helps the eyes lock in on the moving object once they’ caught up with it.

The low level mechanism works before the saccade movement, i.e. before the eyes quickly dart across to look at the object, but the high-level mechanism seems to be a position-tracking speed estimation mechanism.

What I found very interesting was how this result was reached. In the study, some participants’ eyes were able to catch up to a moving object easily, while others were better able to lock in on the object once their eyes caught up with it. This neat division into two groups led to the deciphering of these two modes of motion perception.

So if you’re terrible at tennis like me, now you have excuse If you want more info about eye movements, Wikipedia (of course) has a good page. Liverpool University has a more technical write-up.

[tags]smooth pursuit, eye tracking, motion perception[/tags]

Video is the Next Big Thing on the web right now. It is very easy to capture, produce, and distribute a video these days, and it’s getting easier by the day. In the last few weeks, I’ve come across two very interesting sites dealing with science videos.

First up is Scitalks, which collects interesting videos from around the web into one place. Anything relating to science is game here, and so you get a very diverse set of videos. The only thing missing (or couldn’t see!) is an RSS feed for the videos. Not necessarily a terrible thing but certainly useful for many people. Go check it out. I can’t recommend it enough!

Second one is ScienceHack, which is a video search engine of sorts. I say of sorts because they claim it’s human edited (their exact words: "every science video on ScienceHack is screened by a scientist to verify its accuracy and quality"), which makes it more of a searchable directory than a search engine. This is an absolute necessity if you want to maintain quality as there are plenty of rubbish videos out there claiming to be scientific. Still, as ever, always double-check everything you read/see out there (even in print, and yes, even here on blogSci).

So, two very useful sites for you scientific videos needs. Enjoy

[tags]science, videos[/tags]

Another exciting week in science. Here is a quick round-up.

• How do you make transparent electronic paper (e-paper)? Why, with transparent transistors of course. The transistors are made of single “nanowires,” or tiny cylindrical structures that were assembled on glass or thin films of flexible plastic.
• Electronics and biology are becoming better friends. To develop selective measurement techniques for diagnostics, drug research, and the detection of poisons, researchers at the Max Planck Institute for Biochemistry in Martinsried/Munich have created a bioelectronic hybrid system. The new system does not kill or damage the cell, allowing for better measurements. Their test was using serotonin.
• What are the effects of cigarette taxes? A new study found that cigarette taxes do reduce smoking but can lead to bootlegging. Lead researcher Dr Donna Shelley noted, "Although interest in quitting was high among the smokers interviewed, bootleggers created an environment in which discounted cigarettes were easier to access than cessation services." This just shows that any public health policy needs to be approached from multiple angles for it to be effective.
• Still on smoking, it turns out that second-hand smoke leads to elevated levels of carcinogens in people. The research showed that nonsmoking restaurant and bar employees absorb a potent carcinogen -not considered safe at any level- while working in places where they had to breathe tobacco smoke from customers and co-workers. The carcinogen, NNK, is found in the body only as a result of using tobacco or breathing secondhand smoke.
• Finally, another smoking-related find, but this one offers hope: What Happens to Your Body if You Stop Smoking Right Now shows the timeline of events that your body goes through once you stop smoking. Hint: the effects start in 20 minutes!