From the young island nation of Palau, nestled in the warm waters of the Pacific Ocean 2000 miles south of Tokyo, comes news of a most peculiar fossil find. It's too soon to say if it's a clever hoax, a new species, or just unusual variation in an all too familiar critter. Early reports suggest that island dwarfism was hard at work in the relatively recent past. But hold on to your hat, because this time the species downsized by the long sharp scalpel of natural selection, may have been us. Via Afarensis:
PLoS -- Preliminary analysis indicates that this material is important for two reasons. First, individuals from the older time horizons are small in body size even relative to "pygmoid" populations from Southeast Asia and Indonesia, and thus may represent a marked case of human insular dwarfism.
Hominid plasticity: Human Evolution. For creationists it's the crux of controversy. And don't think for a second this belief is only present among conservatives. A 2004 poll shows that almost half of all Kerry voters believed that "God created humans in their present form." But the evidence for human evolution is immense.
Well, we can assume most creationists are busy this morning, and there is a lot of new blood coursing through the veins of Big Orange. So in hope of placing this new find in some scientific context, a short survey of a few evolutionary highlights and a poll on human origins is in order right here, right now, on Sunday Kos.
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In the early days of biology it quickly became obvious that living creatures have changed radically over time. Plants and animals were alive that could not be found in the fossil record, there were plants and animals in the fossil record for which there were no living representatives found in the late 18th century.
Because of comparative anatomy and physiology, many of those early biologists had come to suspect that groups of living things were somehow related, distant kin, but they lacked a testable explanation for transmutation of species. What Charles Darwin did was to provide that explanation, and more importantly, he backed it up with observed data gathered in his younger days while on a long ocean voyage aboard the HMS Beagle. Darwin's insight was built on several observed facts:
More offspring are born than the environment can support.
Intense competition ensues among those offspring for finite resources.
There is variation among those offspring lending some of them a competitive edge.
At least part of that adaptive variation can be inherited.
Darwin inferred that the environment could naturally select for advantageous traits in plants and animals in much the same way humans had done so using artificial selection to domesticate plants and animals. His resulting inference was that over time, those changes build up, and over long periods of time the accumulated change could be dramatic, giving rise to one or more completely new species. This was Darwin's original theory, Descent with Modification, to explain the Origin of Species. That theory, like any scientific explanation, is logical, consistent, and makes testable predictions. One of the more controversial predictions, at least to creationists, is common descent. Specifically, humans share a common ancestor with other animals, such as chimps or primates or dogs.
Much of the evidence for common descent, be it whales or humans, revolves around two items Darwin would have readily understood, biostratification of the fossil record and transitional fossils.
Biostratification simply means that ancestors are found in the fossil record before descendants. Fish appear before amphibians, reptiles are found before birds, mammals appear before whales or humans. Imagine how easy this would be to falsify: one partial skull of a modern dog found in situ in the entire fossil record during or before the reign of the dinosaurs would threaten it. And yet there's not a single such piece of evidence.
Transitional fossils are remains which show a combination of morphological traits straddling two recognizable groups of living creatures, or clades. Again one single transitional fossil found out of phylogenetic sequence, a half-monkey and half-butterfly for example, would be enough to discredit that enormous body of data.
Left: A scene from 50 million-years ago, Ambulocetus, a transitional 'walking' whale chomps on an early horse. Right: Australopithecus, 3 mya, next to the paleo-wildlife artist who created both images, Carl Buell.
One of the more fascinating lines of evidence for common descent comes from a field Darwin and his contemporaries were completely unaware of: molecular analysis of genetic material. One example comes in the form of a genetic 'scar.' Viruses insert themselves into the genome and turn it into a virus making machine. Sometimes the little bastards will get into the DNA, successfully replicate a few hundred times, the copies reinserting back into the genome, before the body's defenses shut them down. Once deactivated, those little scraps of viral remnants remain in the genome, like a signpost saying "Mr. Virus, was here". We can tell they're viral because they code for proteins not used in eukaryotic (Animal) cells such as viral enzymes. These preserved viral scraps are called Endogenous Retro-viruses or ERVs for short. And if they happen to lay near or within a stretch of DNA that confers an adaptive trait which becomes ubiquitous in the entire population, every member of that population will have that ERV in the exact same location[s]. Or courtesy of BonoboBill, in video.
Well, it so happens humans and chimpanzees have at least seven of the exact same viral base pairs sequences in several hundred respective locations in their respective genomes. We know how that can happen; chimps and humans shared a common ancestor. We can also estimate how long those shared sequences between chimps and humans have been around, because there are slight, random changes to the sequence over time. The hands on the molecular clock point to about 6-8 million years. Which just happens, oddly enough, to be exactly what the fossil evidence would suggest for a split between the ancestors of chimps, and the ancestors of humans.
Another example from modern genetics are repeat elements like SINES and LINES. Humans share these sequences with chimps and dogs and rodents. But where a repeat element unique to humans and chimps happens to overlap another shared between humans and mice, the human-mouse sequence is over written by the human-chimp sequence; never the other way around. These patterns match the biostratification of the fossil record by confirming that the common ancestor of humans/chimps is more recent than the common ancestor of rats/humans. And these two examples, ERVS and repeat elements, are a tiny fraction of the genetic evidence. There's enough published scientific work in genetics or molecular biology that only makes sense in the light of evolution to keep you busy reading for life.
The genetic evidence for human evo isn’t just a smoking gun, it’s a video of common descent pointing the weapon and pulling the trigger.
Common ancestry is now so well supported that if the theoretical process by which species change and diverge were to be discredited, it would be necessary to find another explanation consistent with common descent. Evolutionary biology also interlocks perfectly with prior evidence from a variety of independent sources, developmental biology and homology, the age of the earth and universe, physics, plate tectonics, organic chemistry, and so on. The modern form of the theory of evolution which unifies all this evidence under a single, coherent explanatory framework is called the Modern Synthesis. That explanation predicts that under certain intense selective pressures, and especially in a relatively small, geographically isolated population such as those found on islands, even routine variations in height or weight can provide plenty of change for natural selection to act upon quickly.
This is what happens in cases of insular dwarfism. Trapped on an island with limited resources, creatures once large can evolve into smaller versions (Interestingly, very small creatures like lizards or mice living on relatively large islands in the absence of larger predators can evolve into giants). It's happened to mammoths, hippos, and even dinosaurs. A few years ago the paleo-anthropology community was rocked by the discovery of what appear to be primitive, dwarf hominids on a remote island in Indonesia called Flores.
Which brings us to today: Whereas the comparatively small-brained "Hobbits" (H. floresiensis) from Flores date from a range of 15,000 -- 90,000 years ago and may represent a population of dwarf hominids descended from something like H. erectus, based on the limited information released, these "Palau Pygmies" sound much more like anatomically modern humans. Except they were petite -- a little over one meter in height and weighing roughly 70 pounds!
Even more stunning, the abstract states they could have still been running around on one side of the world while the Roman Empire rose and fell on the other. And the real kickers is, if they do turn out to be some sort of subspecies that evolved from modern man, that would make us the transitional species to them.
