Every Brit of a certain age can recognise a Morris Minor by the iconic shape of its bonnet.
What most don't realise is that when Alec Issigonis designed the car in 1948 he had a last minute change of mind. He realised it looked too narrow. He cut the full-sized model in half lengthwise and experimented until settling on an additional 4 inches. However the factory had already built the tools for the bonnet body panel so a compromise was agreed. Issigonis added a narrow strip down the middle of the bonnet to achieve the desired width, resulting in the stylish detail that generations have admired ever since.
Issigonis had to make do because of the cost of going back on an earlier design. Evolution has a similar problem. Every change must not only result in a workable design but in an improved design - otherwise natural selection will not favour it. The result is many examples of "Morris Minor bonnets" in the natural world, the best known of which is probably the recurrent laryngeal nerve (RLN). It connects to our larynx and helps us to speak and swallow.
At an early stage of embryonic development known as the pharyngula, comparisons can be seen between all vertebrates - we will return to this in a later post. The RLN can be seen in a fish embryo as the 4th branch of the vagus nerve running alongside the blood vessel of the sixth branchial arch. In adult fish it remains in that position connecting the brain to the gills. In the human embryo the sixth arch becomes a ligament connecting large blood vessels of the heart. Since he RLN is behind this arch it also has to move backwards taking a detour around the aorta.
The result is a nerve that travels from the human brain down the neck into the chest, around the aorta and back up the neck to the larynx. An intelligent designer would have rerouted the nerve to follow a sensible path of just a few inches but this option was not available to evolution.
If this seems strange, consider that all other vertebrates have the same restriction. Once the route was set in our fish ancestor untangling the wires has never been a possibility. In the giraffe the RLN has to take a 15 foot detour.
The same arrangement must have existed in dinosaurs including the massive Supersaurus whose RLN took a detour of a stunning 92 feet.
Issigonis went on to design the Mini in which he implemented many of the design ideas he was unable to include in the Morris Minor including the brilliant transverse engine. Meanwhile evolution has to make do with bodged modifications of old designs.
|Part 1 - Protein Functional Redundancy||Part 2 - DNA Functional Redundancy|
|Part 3 - ERVs||Part 4 - Smelly Genes|
|Part 5 - Vitamin C||Part 6 - Human Chromosome 2|
|Part 7 - Human Egg Yolk Gene||Part 8 - Jumping Genes|
|Part 9 - Less Chewing More Thinking||Part 10 - Non-Coding DNA|
|Part 11 - Tiktaalik||Part 12 - Lenski's E.coli Experiment|