In addition to being my birthday (!), it's also "Fun with Science" Thursday. In my Thursday posts, I'm going to discuss the more interesting parts of a current scientific development.
Today's story is the latest development in the continuing saga of the "Flores Hobbits." These are unusually small hominids who lived in Indonesia tens of thousands of years ago. Scientists are having a difficult time figuring out where these hominids fit into the scheme of human evolution, because they don't follow the prescribed time/space pattern that has been established by hominid bone discoveries in Africa, Asia, and Europe. The newest developments, from two groups that published their work in the scientific journal Nature, highlight that Homo floresiensis is even more confusing than before. Here are the links to the news blurbs from Nature and NYTimes; if you have access to Nature (from a university or library, for instance), I also encourage you to take a look at the primary research articles.
One of the problems that scientists have with the Hobbit bones is that the skull and foot sizes do not "match." It's been thought that skull size increased as hominids evolved, to allow for larger brains, and that the size and shape of the foot evolved at a proportional rate, to allow upright walking and running. These hobbits appeared to have almost human-sized feet, but those feet were very primitive and may not have supported walking; despite the large feet, the hobbits had extremely small skulls, comparable in size to chimpanzees'. Thus, they don't fit neatly into the "timeline" of human evolution. The two groups take the same foot and skull evidence and come up with two very different conclusions about the evolutionary identity of the Flores Hobbits. One group thinks that the Hobbits are relatively highly evolved, but are victims of "island dwarfing," a phenomenon where animals confined to islands are under selective pressure to reduce the size of some or all of their body parts (Weston and Lister, 2009). The other group believes that the Flores Hobbits may not be dwarfs, but may be much more primitive hominids, and may not be ancestors of modern human beings (Jungers et al., 2009).
I took a class at MIT about human evolution and paleontology, and I left the class more confused than when I entered it. People want to believe that humans evolved in a neat continuum, and that branching groups of hominids, who were sort of "human-like" but did not "turn into" humans, were a very minor occurrence in evolutionary history. This seems to not be the case, and the Flores Hobbits seem to provide support to this idea. There were lots of groups of hominids that share features of human beings, but for one reason or another (usually bone structure or skull size) are thought to not contribute to the homo sapiens lineage. The best known example of this phenomenon is the co-existence of Neanderthals and humans in Europe until around 30,000 years ago. Another example, better known in paleontology fields, is the group of Australopithecus species, many of which are not thought to have evolved into Homo sapiens.
I think that the existence of these non-human hominids is a really great way to highlight the fact that evolution doesn't have a "goal." All primates are not on the path to becoming human, and Homo sapiens may not be the "optimal" hominid species; it was just the one that became dominant at some point in the distant past.