These fish can tell us a lot about ourselves.

Species often end up a different color when their environment changes. And humans are no exception.

When people moved out of Africa tens of thousands of years ago, they were dark-skinned. Now when we look around Northern Europe or parts of Asia, we see much lighter people. What happened?

A common explanation has to do with sunlight and vitamin D. When people moved north, they got less sun. Less sun means less vitamin D and awful diseases like rickets.

Anyone who moved north and had lighter skin ended up getting more vitamin D and did better than their darker neighbors. After awhile, most of the population had light skin.

This is all well and good, but what happened at the gene level to cause this transformation? One way scientists are learning about how humans ended up with lighter skin is by studying fish. For example, the zebrafish has taught us a lot about why Europeans are often so pale.

The zebrafish is an important model system that scientists use to study vertebrate development, human disease, and lots of other things. A common mutant fish that scientists use in these studies is called “golden.” These fish have lighter, yellowish stripes instead of black ones.

Scientists discovered that these mutant fish had yellow stripes because of a single DNA difference (or SNP*) in their SLC24A5 gene. When fish have this DNA difference, they have yellow stripes.

These scientists next looked for this gene in people. What they found was that most of the people they looked at had two copies of the “black stripe” version of the gene. Except for Europeans. They tended to share a common SNP in their SLC24A5 gene that the scientists went on to show is a big part of why many Europeans have lighter skin.

Another group of researchers decided to dig a bit deeper and find out when this transformation happened. By looking at the DNA around SLC24A5, they found that lighter skin came to dominate Europe around 6,000-12,000 years ago. At first this result is a bit confusing because humans moved into Europe around 40,000 years ago. Why did it take so long for lighter skin to become the norm?

Scientists can’t know for sure but one idea is diet. Around this time, Europeans started to grow their own food. And a farmer’s diet has less vitamin D than does a hunter-gatherer’s diet. Maybe the lack of sun only started to affect Europeans after they started growing their own food. Then, after a relatively brief time, most Europeans ended up fair-skinned to get enough vitamin D.

This gene doesn’t explain all of skin color. For example, it doesn’t explain the difference in color between Northern and Southern Europeans. Or why some Asians have fair skin. But it does explain a good deal of European coloration. Thanks, zebrafish!

*SNP=single nucleotide polymorphism

Dr. Barry Starr is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA.

Genetically, we’re all pretty much the same. A massive volcanic eruption 75,000 years ago may be why.

Lake Toba is all that is left of the volcano
that nearly wiped out mankind.Last blog I talked about how East Africans are genetically more diverse than Asians. Who are genetically more diverse than Native Americans.

From all of this you might have concluded that people are pretty different from each other. They aren’t.

People are surprisingly similar at a genetic level. For example, any two people from anywhere on Earth are more similar than two chimps from the same troop. Why are we all so alike?

One possible explanation is that something in our collective past nearly wiped us all out. And we all come from the few survivors who were left.

A likely candidate for this near annihilation event is the Toba volcanic eruption that happened in Indonesia 75,000 or so years ago. This eruption was huge.

It was equivalent to around 1 billion tons of dynamite and was about 3000 times more powerful than the Mount Saint Helens eruption in 1980. It also may have reduced the average global temperature by 5 degrees Celsius, darkened the world for 5 or 6 years, and plunged the world into a new Ice Age.

As you might imagine, this eruption had dramatic effects on species around the world including our own. Estimates of how many people were left range from around 1000-10,000 breeding pairs. The theory is that we are all so alike because we share these survivors’ DNA.

Whether true or not, a bottleneck in our past would not make us unique. Lots of species go through these near death experiences.

Scientists think cheetahs went through one around 10,000 years ago. Cheetahs are all so similar genetically that veterinarians can do skin grafts with “unrelated” cheetahs.

And of course, people have created bottlenecks in species too. For example, in the late 1890’s there may have only been 20-100 elephant seals left in the world because of hunting. Now there are at least 150,000 spread across the west coast.

Species are in danger long after they go through a bottleneck. They have a pretty limited gene pool which means they may not be particularly healthy and are in danger of being wiped out by, for example, a single disease. Humans are probably OK in this regard (consider natural resistance to HIV for example) but elephant seals, bison, and cheetahs, and many other species may not be.

Fortunately for us we successfully came through our bottleneck. Hopefully, the animals that we’ve nearly wiped out will too.

Dr. Barry Starr is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA.

I love my cell phone. We have a serious relationship. One that may be biologically predetermined.

Let me explain. On New Year’s Eve I brought my phone with me to San Francisco’s Ocean Beach, where I traditionally go, rain or shine, to watch the year’s last sunset. I was by myself, but I wasn’t alone.

Oh no. I took snapshots of shimmering colors on the waves and sent them to faraway, landlocked friends who miss the sea. Another friend called to say she was also watching the sunset from her rooftop. Text messages flowed in.

I was connected.

Well, duh,” you could say.

And this “duh” is exactly what seemed kind of profound: we take communication for granted. Of course we can talk to each other and share things with each other. And of course we create new devices to make talking and sharing easier. Of course.

But why do we do this, seemingly to no end? And why is it that communication is such a vital and defining aspect of our experience as humans? Why, really, do I love my cell phone so much?

I think it’s genetic.

It’s probably not news to most of you that we humans appear to be wired to talk to each other. We’ve got that FOXP2 gene that keeps making the news, contributing to our linguistic capacity. In fact, many researchers believe that language was central to our success as a species and allowed a small group of humans to expand across the globe about 50,000 years ago.

Our genetic design for interaction seems to go beyond talking amongst ourselves. A University of Michigan study slated to be published next month found that social interaction has a positive affect on memory and on cognitive functioning. The people who had the most conversations with others seemed to be the sharpest, and this was particularly true among young people. This may mean that more socially-oriented humans had a bit of an advantage over those who tended to keep more to themselves.

We may be such social animals that we’re even hard-wired to simply need company. After all, isolation is one of the most universal methods of punishment. Another set of researchers at the University of Illinois at Chicago found that mice isolated from their comrades have lower levels of hormones that control anxiety, depression, and aggression. They believe that these responses are similar in humans. In other words, it’s possible that our brains keep us happier and functioning better when they’re interacting with other brains.

It makes sense that our predecessors who figured out how to play well with others and share their thoughts were the ones who got the best shot at passing on their genes. And it’s no wonder our species devotes such enormous reserves to inventions that make communication easier. The most basic systems of rock painting and alphabets have allowed groups to share stories or warn others of impending trouble. And creations that help disseminate these symbols–papyrus, the printing press, even the simple pen and paper–have had a major impact on how we exist with one another, as individuals and as societies.

These days, many of our communication technologies have gone beyond “watch for hungry bear” or “here’s my idea” into doing a kind of doubly-human duty. We not only use technology to convey thoughts, but also to extend our opportunities to create bonds with other people and to form social groups. Thus the popularity of the likes of Facebook, personals ads, and Flickr. In fact, if you leave a comment about this little ditty I’ve written, you’ve hopped on this double-duty train by becoming a part of Quest’s blogging community.

And so now, as my thumbs feverishly tap out text messages, I see my cell phone as more than a gadget. It’s the latest cousin of cave drawings and hieroglyphics. What it says about my own evolution I’m not quite certain. But no doubt my wireless admiration results from something buried in my chromosomes.

Robin Marks is a journalist and science writer who current serves as a Multimedia Projects Developer for the Exploratorium in San Francisco, CA.

latitude: 37.7595, longitude: -122.51

NOVA commemorates the historical evolution trial of 2005.

Credit: NOVAIf you tune in or point your web browser to PBS this week, you’ll see a whole bunch about evolution. It’s not Charles Darwin’s birthday, but it’s a celebration that may one day carry much more significance: it’s the two year anniversary of the Kitzmiller vs. Dover trial. In 2005, parents of high school students in the Dover, Pennsylvania school district took the education board to court over attempts to teach intelligent design as a bona fide alternative to evolution in public high schools. The juryless trial assembled a first-rate list of witnesses for the plaintiffs (pro-science, pro-evolution), all of whom eloquently spoke about the foundations of science and evolution, and how we know what we do about the history and diversity of life. Intelligent design advocates, in their defense, had to present evidence supporting intelligent design as a genuine scientific argument. In the end, the judge (who was named one of Time’s 100 most influential people last year) ruled that intelligent design is not science and that, furthermore, teaching intelligent design is unconstitutional. His verdict is well worth reading in its entirety (for legal fans out there), or you can check out summarized versions online.

NOVA online has great clips from the show, including additional interviews elaborating on the science behind evolution. Interestingly, there are many Bay Area connections in the show. NOVA prominently features Oakland-based National Center for Science Education (including Eugenie Scott and current Cal graduate student Nick Matze), clearly reflecting the center’s long-standing support for science standards in education, especially in biology. Kevin Padian, a Cal professor in integrative biology, provided articulate explanations of evolution as part of his expert testimony, and many of the clips on the website include examples that are now textbook cases of evolutionary processes, some of which are explained the on the Understanding Evolution website, hosted by the UC Museum of Paleontology and the Berkeley Natural History Museums.

Overall, the case is now seen as a landmark event in the on-going battle of teaching evolution and championing science literacy in the public. Intelligent design, which is really creationism in a different guise, fails in clear and dramatic ways to explain the natural world in the way that evolution, by natural selection, has successfully done for over 150 years. For more, be sure to check out the NOVA online features or the Understanding Evolution websites. After all, who doesn’t want to live in a scientifically literate society?

Nick Pyenson is a PhD candidate at the University of California, Berkeley, in the department of integrative biology and the museum of paleontology.

latitude: 37.7819, longitude: -122.286