Continuing on...
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One of my favourite things to bring up when chatting to Creationists are atavisms. In their response, I only ever get silence, unrelated meandering or a loud exclamation of "falldidit!".
So, what are atavisms...?
Atavisms are evolutionary throwbacks. Going by dictionary definition - it's the "tendency to revert to an ancestral type". These apparent anomalies occur due to organisms preserving (phenotypical) features in their DNA, they're simply deactivated and thus not expressed. However, a random mutation occasionally occurs which reactivates these genes. This results in the creature having (sometimes) primitive and ancestral features. For example, if a grandfather had a specific trait or characteristic that was not present in any of his children, it is still possible for the grandchild (or great, great grandchild) to possess such a feature. This is because the genes are still there in all the intermediates between the grandfather and the great grandchild, they were simply not expressed.
Some interesting examples...
Whales with legs:
As I hope you know, whales don't have legs. They do, however, have a vestigial pelvis. This is because whales are descended from terrestial mammals that had hindlimbs. It is argued that the pelvis is still utilized, although this is more of an evolutionary workaround and modification of function. It is still not the original and obvious function that it once performed. The interesting thing is, though, is that there have been multiple cases in which whales have been found with functional atavistic limbs attached to the vestigial pelvis. From an exterior and superficial glance, they simply appear like extra hind fins as opposed to legs, but if you examine the anatomy - the "fins" include fully formed femurs, tibula, fibia and digits (toes). These aren't the sole result of random mutations (only the reactivation of present genes), the information must be already there. Such features don't spontaneously spawn in individual organisms unless they're of atavistic nature.Chickens with reptile teeth:
Another one of my favourite examples of atavisms is from chickens. It goes as follows: chickens don't have teeth. They did evolve from creatures that had teeth, however; dinosaurs. This means it's possible that chickens may retain the genes required for the growth of such choppers. As it turns out, they do. Scientists have even been able to induce "alligator-like" tooth formation in chicken embryos. This is only possible because of the genes being present, which, according to Creationism - they really shouldn't be.
Tailed humans:
During embryological development, all humans develop tails which later recede. Once again, this is because the genes are still present. A better example (and all the more difficult for Creationists to deal with), is when humans are born with tails. Some Creationists try to cast these evolutionary gems off as simple malformations: mutations with no trace of an ancestral state. However, they never address "true" tails (pseudo tails are simple skin and fat). That is, a functional appendage with skeletal, muscular and voluntary control, including vertebrae, nerves and muscle. This is not a simple "malformation". Just like the mamalian eye, it's an evolutionary "throwback", a biological legacy and a reflection of our history. It's an atavism, Creationists, deal with it. Other:
There are many other great examples. Eg, snakes with hindlimbs, re-emerged extra toes on horses, ulna and fibula found on minature horse, hind fins on dolphins, people with enlarged ape-like canine teeth etc.
Creationist response:As I said earlier, I rarely get a related response when I bring this up. The few times when I do receive a reply (and when it's not the typical meandering or blaming of the Fall), I get the image to the left shoved in my face along with "does this mean we evolved from goats?!" and a sly smile, as if they've just proven science wrong. Creationists - that's not an actual horn! Cutaneous horns are unusual tumours which seem to be caused by exposure to radiation over a long period of time. Mrs. Zhang Ruifang didn't have any goat-leftover genes reactivated. It's not an atavism, move on.
Potential falsification:
Atavisms must only show features included in the species evolutionary past - they must be ancestral. Otherwise, we either messed up the family tree or we have much more to learn about these odd reappearences. They must only revert to the ancestral type. Yet, there are absolutely no examples of atavisms contrary to the phylogenetic tree, ie, reptiles with fur. They all follow what evolution expects and predicts them to follow, nothing else.
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Another slice of evidence for evolution. If you're a Creationist, I'd love a response explaining how you fit them with your beliefs, since these are fantastic indicators of a complex evolutionary past.
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Thoughts?
