Chelicerata is the class of arthropods whose members are characterized by appendages (chelicerae) that appear before the mouth. The class includes species of spiders, ticks, mites, scorpions, horseshoe crabs, as well as others, including the extinct sea scorpions (pictured left). The common ancestor lived back in the Cambrian period.
Yale University's Peabody Museum of Natural History has put together a video that looks at the chelicerata evolutionary tree from a different perspective. They've used morphing technology to show the transformation of the ancestral Cambrian progenitor into each of the major sub-groups. Of course it's not perfect. For one thing, the ancestor must be an approximation based on the fossils of the time. Also, photographic morph isn't the most accurate depiction of how evolution works--especially when transitional fossils are sparse. Different body parts change at different rates and often go through stages that don't fit into the progressio of pictures in the morph.
Having said that, it's a very cool video. Check it out!
Today is the 200th anniversary of the birth of Charles Darwin. He is undoubtedly one of the most influential people in history. His Ideas are the cornerstone of modern biology. In fact, before Darwin, biology didn't really exist; or as Theodosius Dobzhansky famously said "Nothing in Biology Makes Sense Except in the Light of Evolution". His ideas about common descent and natural selection have even leaked into other branches of study such as linguistics and sociology. But his ideas didn't come from a vacuum; they weren't based on observation alone. He borrowed from thinkers in other fields.
Just how did he get there? For starters, Darwin began his studies with the intent of becoming a doctor. He found that he didn't have the stomach for surgery, so he switched to theology. A country vicar was the future that young Darwin saw for himself even up until he set sail on the Beagle. But even so, it was the study of nature that captivated him. As Janet Browne recounts, he was especially interested in a man whose ideas Darwin would eventually make obsolete.
In particular Darwin engaged with the theological views of Archdeacon William Paley, initially as part of his syllabus and then as independent reading. Darwin was expected to be able to answer questions in the final examinations on Paley's Evidences of Christianity and Moral Philosophy. After he graduated, he read the last of Paley's trilogy, Natural Theology (1802), with its argument that the adaptation of living beings to their surroundings was so perfect that it proved the existence of God. How could such a perfect design have come about, stated Paley, except from the careful hands of a designer? If a watch were accidentally found on a path, we would be entirely justified in thinking that it had been constructed by a skilled craftsman according to some design or plan. Such intricate mechanisms do not suddenly appear out of nothing, like magic. They are made by a maker. So, Paley argued, the world about us must be considered in the same way as the watch.
Darwin was also influenced by Malthus' An Essay on the Principle of Population which stated that populations grow exponentially until they no longer have the resources to maintain themselves, then they are subject to competition, poverty, and decline. Another great influence was Lyell's Principles of Geology which stated that land forms were not always as they as today, but rather formed slowly through natural processes (such as erosion, etc.). Ironically, Lyell specifically made an exception for living things which--of course--were not subject to change in the same way.
Charles Darwin circa 1860--about the time he published Origin of Species
Now contrary to popular opinion, Darwin didn't come up with his theory while observing all the different forms on the Galapagos. While he did note the variation from island to island with interest, it wasn't until he got back home and started to study his logs and samples and then really think about them deeply that his theory began to form. And once it formed, he took his time to get it right. Twenty years passed between his first documented mention of the idea and the publishing of Origin. The reasons for the delay are often debated among scholars, but what is for sure is that when he did publish, every i was dotted and every t was crossed. "He examined the minutiae of nature" notes biologist and writer Olivia Judson in today's New York Times "but worked on grand themes."
Could plants from the mainland colonize a newly formed island? If so, they would need a way to get there. Could they survive in the ocean? To find out, he immersed seeds in salt water for weeks, then planted them to see how many could sprout. He reported, for example, that “an asparagus plant with ripe berries floated for 23 days, when dried it floated for 85 days, and the seeds afterwards germinated.” The Atlantic current moved at 33 nautical miles a day; he figured that would take a seed more than 1,300 miles in 42 days. Yes, seeds could travel by sea.
Here are the first couple paragraphs from chapter IV of Origin, where he begins to explain his notion of natural selection.
Be sure to check out the other Darwin Day posts at Blog for Darwin Carnival.
Now let me finish my Darwin Day post with a shout out to my favoritest and adorablest nephew, Rafael Darwin.
Atrios is right, though I’d put it a bit differently: centrism is a pose rather than a philosophy. And to support that pose, the centrists are demanding $100 billion in cuts in the economic stimulus plan — not because they have any coherent argument saying that the plan is $100 billion too big, not because they can identify $100 billion of stuff that should not be done, but in order to be able to say that they forced Obama to move to the center.
Which raises the obvious question: shouldn’t Obama have made a much bigger plan, say $1.3 trillion, his opening gambit? If he had, he could have conceded to the centrists by cutting it to $1.2 trillion, and still have had a plan with a good chance of really controlling this slump. Instead he made preemptive concessions, only to find the centrists demanding another pound of flesh as proof of their centrist power.
This is exactly right. A political centrist's ideal stimulus package isn't objective in the sense before introduction of the bill, there is no $ amount attached to it. The Republicans are certainly objective--they're looking for a stimulus package with $0 spending. The Obama administration's bill is (or should be) objective--the stimulus package should be large enough to prevent a major economic melt down. But the centrist's stimulus package is subjective in the sense that the $ amount that it should be is subject to the president's proposed number--it needs to be somewhat less so that the centrist can claim to be reasonable. But the actual number is undetermined until Obama fires first.
The Obama administration has received an F on their first quiz in Negotiations 101. Let's hope that they're fast learners.
