March 14, 2007
Hairy Question Untangled By Lice
I cannot say I have ever pondered when we, as former apes, dispensed with the body hair. I guess I assumed it must be at some point after we had either solved the body warmth & protection problems ourselves (through living arrangements or the invention of fashion) thus making body hair obsolete, or if the problems didn't exist because we were living in such a warm habitat that it was a detriment (if so, why didn't other species change at a similar time?). Still, had I decided to ponder this question, it has some interesting problems associated with it. Hair, skin and cloth are not particularly durable or long-lasting materials like fossils. Over time, they deteriorate and our evidentiary support disappears.
Luckily some clever scientists out there came up with a very interesting way of dating when we shed our body hair for good without the need for evidence. They untangled this puzzle by looking not at humans, but at the evolution of another species that was intimately linked with them. You got it, those lovely little lice!
Stoneking, an evolutionary anthropologist, had a hunch that he could calculate when body lice evolved from head lice by comparing the two varieties' DNA, which accumulates changes at a regular rate. (It's like calculating how long it took a typist to produce a document if you know he makes six typos per minute.) That fork in the louse's family tree, he and colleagues at Germany's Max Planck Institute for Evolutionary Anthropology concluded, occurred no more than 114,000 years ago. Since new kinds of creatures tend to appear when a new habitat does, that's when human ancestors must have lost their body hair for good—and made up for it with clothing that, besides keeping them warm, provided a home for the newly evolved louse.
If you had asked paleoanthropologists a generation ago what lice DNA might reveal about how we became human, they would have laughed you out of the room. But research into our origins and evolution has come a long way.
More At: Newsweek: Beyond Stones & Bones
The article above is certainly about more than just this lousy discovery, but I thought that was the most eye-opening. This critical look at inter-species relationships, symbiotic or otherwise, and how scientists are using them to help determine events of evolutionary importance in a species is fascinating. Think of all the stuff living in us, on us, around us. The bacteria alone could answer much, if we can just figure out what questions to ask.
Posted by sorsha at 11:27 AM | Comments (1) | TrackBack
February 24, 2007
Ancient Amphibians
Fossilized Frogs.. Ancient Amphibians... Ribbiting Run-in With Resin... Jurassic Jumpers... Well, not really Jurassic period, but the more recent the Paleogene period, which was about 125 million years younger than the Jurassic period.
Regardless, there's been a great discovery of a fully intact tree frog encased in amber. Some people are talking about trying to follow Michael Crichton and extract its DNA, but its unclear whether or not the collector will allow this to happen.
A miner from Mexico's Chiapas state has made the find of a lifetime—a tiny tree frog preserved in amber that could be 25 million years old
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The block of amber, or fossilized tree resin, encasing the 0.4-inch (1-centimeter) frog
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The specimen appears to belong to the genus Craugastor
More At: National Geographic: Ancient Tree Frog Found Encased in Amber
I couldn't find much on Craugastors, other than its a group of frogs from Central America, many of which are critically endangered or extinct. I did find an article that talked about the origin of the Craugastors. The group of Craugastors, which contains over 100 frog species, is monophyletic. This means that the group all had a common ancestor. That ancestor (mommy of of all Craugastor species) looks to have appeared in northern Central America from South American in the early Paleocene epoch, which was about 56-66 million years ago.
Half the time I was finding that Craugastor was a subgenus and then a genus. What appears to have happened is that these frogs were originally lumped into a larger genus called Eleutherodactylus, but once the common ancestor was found, the Craugastor group was extracted from this larger genus and elevated to its own genus.
Still, taxonomy is slippery stuff, scientists do not always agree on how to classify organisms. The original methods involved only what could be observed. Then came DNA and other more intimate methods of determining how species have evolved.
Here's an example of what I mean... some groups like Craugastor are formed (or re-formed) because genetics supports their cohesiveness as a group at the genus level. However there is another genus that seems to have split from Eleutherodactylus but the primary reason for the grouping is all frogs in the group supposedly lack vomerine teeth. Now here we have a physical characteristic for classification that does not necessarily make for a cohesive group from a genetic perspective. We might infer that this group is going to be closer (family-tree wise) to other reptiles and amphibians that do not have vomerine teeth, like geckos. Still, this is just a visual observation and it is possible that the species both evolved seperately to not have the teeth or to have the teeth, as it may be.
Still don't see why physical characteristics might not be the best way to indicate closely related animals? Let's assume that someone decided to put all green lizards together as evolutionarily similar, assuming that their color was their primary distinguishing trait for grouping. Unless other factors are considered, a green lizard on the other side of the world or in a very remote location would likely be put in the same group, even though it might be very hard to see how they could possibly come from a shared ancestor from so far away. Now consider that perhaps the actual distinguishing trait on these groups of lizards is that a set of closely related lizards learned to blend in with their surroundings, not just be green. You might find that a lizard living in a green environment and another living in an orange, rocky environment just down the way are more closely related evolutionarily than the group of green lizards.
Posted by sorsha at 11:42 PM | Comments (0) | TrackBack
May 1, 2006
Thoughts A-Slitherin'
Isn't it funny how just when you've been thinking about something, the topic pops up in the news?
Take snakes, for example. We just returned home from a lovely trip to Maui in the Hawaiian Islands. There are no snakes native to Hawaii, but we certainly saw lots of eels while snorkeling (see the one above). I'd always assumed that snakes were rather primitive (or at least older reptilian species compared to most creatures of the day) and that they had likely originated in the oceans in the forms of ancient eels. After all, most life originated in the oceans, and I generally consider land and freshwater species to be "newer" than most ocean critters.
It got me wondering why Hawaii would have eels but not snakes. Sure, the islands are quite remote, but still. It seems the perfect habitat for snakes to live - lots to eat, some parts desert, others rainforest. There are certainly snakes in the islands of Oceania and Southern Asia.
Upon returning home, I was catching up on my podcasts, including Nature's podcast. This science journal podcast covered a recent fossil finding that suggests that snakes as they are now may very well have originated from footed creatures on land, not from water serpents as many previously thought.
An ancient snake with hips connected to its spine might be proof that slithery serpents originated on land, not in the water, a new fossil find reveals.
The fossil snake—which has a primitive pelvis and robust, functional legs outside the ribcage—dates from about 90 million years ago.
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The species, named Najash rionegrina, is the earliest limbed snake ever found in a fully terrestrial deposit
More at: National Geographic: Snakes Evolved on Land, New Fossil Find Suggests
Posted by sorsha at 3:18 PM | Comments (2) | TrackBack
June 9, 2005
DNA Of the Cave Bear
I hadn't really considered how DNA mapping could really help clear up some of the questions in the evolutionary family tree. The scientists used the well-documented complete map of a dog's DNA as a crib sheet for determining the appropriate mapping of an ancient species of cave bear (like there are bears that don't like caves?). They found that the cave bear was more closely related to the brown bears (like the grizzly and Kodiak bears) than to the black bears (Yosemite). Truthfully, I would have put money on the brown bears even without such scientific evidence. The black bears in California are more like pets than wildlife nowadays, and they just don't seem as smart - more like gigantic raccoons.
Scientists have sequenced the DNA of two cave bears that roamed the Austrian Alps some 40,000 years ago. It marks the first time researchers have been able to completely sequence the DNA of a species that has long been extinct.
The research opens the door to sequencing the DNA genome of other extinct species, including the Neandertals (often spelled "Neanderthals").
More at: Ancient Bear DNA Mapped -- A 1st for Extinct Species
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