If you look at the universe and study the universe, what you find is that there is no evidence that we need anything other than the laws of physics and the other laws of science to explain everything we see. There's absolutely no evidence that we need any supernatural hand of god. -- Lawrence Krauss, World-Renowned Physicist
There is probably no other notion in any field of science that has been as extensively tested and as thoroughly corroborated as the evolutionary origin of living organisms. -- Encyclopedia Britannica
FAITH. No one word personifies the absolute worst and most wicked properties of religion better than that. Faith is mind-rot. It’s the poison that destroys critical thinking, undermines evidence, and leads people into lives dedicated to absurdity. It’s a parasite regarded as a virtue. -- PZ Myers
Religion is the antithesis of science, an anesthetic for the mind that disables critical thought and encourages the acceptance of inanity as fact, and wishful thinking as evidence. -- PZ Myers

Sunday, July 8, 2012

Evidence for evolution you can see with your own eyes



The limbs of tetrapods all have the same pattern of bones. Darwin was one of the first to comment that it seems unlikely that this single skeletal structure could be the best one possible for each of the activities it is required to perform in different animals. The explanation for this common structure lies in a common heritage -- a pattern of development laid down in the ancestor of all modern tetrapods and adapted over time, by different environmental pressures, to perform different functions.

If you want to see concrete evidence of evolution, look no further than your hand or your foot. Five fingers, five toes. There's nothing magical about the number, yet five digits at the end of their limbs is a motif that runs through all the animals with four limbs, called tetrapods. Even when there are fewer than five digits in the adult animal -- as in horses' hooves and the wings of bats and birds -- it turns out that they develop from an embryonic five-digit stage. There is nothing inherently advantageous about five digits. Nor is there any environmental pressure that favors five digits on the operating end of four-legged animals' limbs.

Pentadactyly (having five digits) is, in fact, an accident of evolutionary history. All tetrapods descended from a common ancestor that just happened to have limbs with five digits. And over the eons of evolution following that, natural selection worked with variations on pentadactyly rather than starting over again to produce tetrapods with another number of digits, be it two, seven, or 17.

The pentadactyl limbs that tetrapods far and wide all have are examples of homologous structures. The term refers to similarities among species that are inherited from common ancestors. Such similarities are not necessarily functional -- that is, there's no physical reason why the body parts are similar based on the tasks they perform. (When body parts resemble each other for functional reasons, they're called analogous structures.)

Critics of evolution argue that species were created separately in their distinctive forms and didn't descend from common ancestors. But the prevalence of the pentadactyl limb argues just the opposite: That for whatever prehistoric reasons, an ancestral tetrapod had five digits per limb, and all of its descendants did as well. The similarity isn't restricted to the ends of the limbs -- the bones of the arm, forearm, and hand of different vertebrates form a recognizable pattern, even though they have been adapted to different functions. And aspects of the nerves, blood vessels, and other tissues in the limb reveal other homologous structures.

Homologies are also seen in other structures, and can even be found biochemically, in the very genetic code that stores information for reproducing individuals. These molecular homologies provide some of the best evidence of a single common ancestor for all life on Earth.

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