Friday 1 November 2013

Evolution's Relics

Our genes have a very long history. 99% of them were in other species before they were in Homo sapiens.

About six million years ago they were in Africa in an ancestor we have in common with the other African apes. Three million years ago they were in the bipedal chimpanzees-like apes called Australopithecines in Southern and Eastern Africa. 375 million years ago most of them were in early amphibians that had recently evolved from lobe-finned fish to move out onto the land. 160 million years ago they were in the earliest mammals.

So it's not surprising that they still produce a few structures that were useful to something else but are no longer useful to us.

Scientists have identified several things that we no longer need and some that, although we no longer need them for what it was originally used for, have been adapted for another purpose. The appendix, for example, is no longer needed to aid digestion of cellulose like it is in some herbivores but serves a useful, though non-essential, role in the lymphatic and immune systems.

Examples of these vestigial fossils which we carry around are:

Darwin's Tubercle
Rather unfairly named after Charles Darwin who noticed it on a sculpture by Thomas Woolner (who is thus credited with having first recorded it) and called it a Woolnerian point. This is a small cartilaginous nodules which many people, including me, have on the upper margin of their outer ear. It is a remnants of the points seen on the ears of many primate and may be the remnants of joints which allowed the top of the ear to rotate or bend to help with hearing or to determine the direction a sound was coming from.

These tubercles are regarded as a minor congenital defect but their inheritance is interesting, suggesting it was once essential. It is inherited according to an autosomal dominant pattern which means you only need one parent to carry the gene to inherit it. However, because of the way it develops in the embryo, it does not always express, even in people who carry the gene. Many structures develop in the embryo under the control of hox genes which act as switches to switch other genes on or off.

The outer ear develops from five small hillocks of tissue calls the hillocks of Hiss which fuse together as they grow. Darwin's point forms at the junction of the fourth and fifth hillock. Normally its formation is overridden by other factors which have subsequently evolved to give the final shape to the human outer ear. It reflects the dynamic tension between two competing control mechanisms, neither of which have a great bearing on survival and particularly on reproduction, so there is no significant selection pressure to remove the point altogether or to refine the control mechanism further.
Darwin's Tubercle on Homo sapiens and Macaca fascicularis
Tail Bones
Humans are not, as many people think, entirely tailless. Our tails are small and internal and consist of a few poorly-formed bones at the end of our spinal column known as the coccyx. You can just about feel it if you try. The fact that these bones are variable both in shape and in number - we usually have between three and five - is a sure sign that they are vestigial. They have been co-opted as anchor points for small muscles that keep the anus in place.

In the developing embryo the number of vertebra is determined by a hox gene which switches off when enough vertebra have formed. This switching mechanism is slightly imperfect and poor timing can result in a variable number of coccygeal vertebra forming. There are even occasional reports of babies being born with small tails.
Goose Bumps
Although not technically structures, good bumps are the result of a vestigial reflex and otherwise useless small muscles called arrector pili in the skin. They result from these small muscles attached to the base of hairs pulling the hair to make make it stand up. This originally served to fluff up our fur when cold so it acted as an insulator, and to make us look bigger when threatened. We still hqave the mechanism even though our hair is totally innadequate for either purpose.
Vomeronasal Organ
The vomeronasal organ is a pair of structures in our nasal chamber. In many mammals they detect pheromones - chemical 'messengers' that convey information about gender, reproductive state, etc. In humans they have been shown to have no function, having none of the nerves by which in other mammals information is conveyed to the brain. It has also been shown that the genes which in other mammals encode for the receptors on the surface of the organs are inactive pseudogenes in humans.

It seems that whatever information we get from pheromones - and we do get some - is adequately catered for with our normal sense of smell.
Wisdom Teeth
I recently blogged about wisdom teeth when the hilariously gaff-prone Young Earth Creationist, Ray Comfort, let it be known without the slightest hint that he understood the irony of it, that he was due to have an impacted wisdom tooth surgically removed.

Wisdom teeth are vestiges from when our ancestors had a more simian-like muzzle as they needed to process large quantities of raw plant matter. With the advent of cooking, and as our face became modified to its present flattened shape with receding maxilla the room for the third molar was reduced and the need for them was diminished. A few people now fail to develop wisdom teeth at all. They are also absent in a few populations, notably indigenous Mexicans. Individuals without wisdom teeth have the PAX9 gene so it seems we have an example of human evolution in progress.
Plantaris Muscle
The plantaris muscle is a muscle in the lower leg which was believed to have been used to flex the big toe during tree climbing in our arboreal ancestors. It now serves no discernible purpose and is absent from 7-10% of the population. It is sometimes surgically removed to be used elsewhere in reconstructive surgery.

These are only a few of those found in modern humans. You could take any other species and find examples of the redundancy which evolution produces over time and which simply makes no sense at all as the work of an intelligent designer.

I would love to see a rational creationist explanation of these redundant structures and how they fit into an intelligent design theory of biodiversity. I assume a professional liar for the Discovery Institute is currently working on a way to dismiss them, or maybe, like so many other problems for their idiotic theory, they are simply relying on the scientific ignorance of their target audience.

Any creationist up for it or would you rather not face up to these sorts of problems for your evidence-free notion?

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