The Common Ancestry Thread (page 11)

cofty

Good points about the mamotremes Still Thinking.

On another thread I posted a video where the Laryngeal nerve of a giraffe was dissected and it could be clearly seen that although it is perfectly functional its design is suboptimal in that it follows an extremely convoluted path as it derives from the Vagus nerve at the base of the brain, runs down the neck, meanders past the cardiac arteries and travels back up the neck to the larynx. An intelligent designer would simply have connected the larynx to the brain using the shortest possible route. This is an example of anatomical sub-optimality.

http://www.youtube.com/watch?v=cO1a1Ek-HD0

There are many examples of this type of sub-optimal “design”, which not only show that many of the resultant structures evolved over time, but also give evidence of common ancestry.

These tissues and organs are not sub-optimal in that they don’t work efficiently, they function very well, but are sub optimal in that their “design” is by no means the most efficient since they have had to build on ancestral structures. It is the utilisation of these structures that allows us to determine common descent through the fossil record or phylogenetics.

One example of this sub-optimal design is illustrated if you have ever choked on you food. Apparently approximately 2500 people choked to death in the USA in 2009. The reason for this is because we cannot breathe and swallow simultaneously, because the mammalian gastrointestinal tract crosses the respiratory system.

The evolutionary reason for this goes as far back to when the Osteolepiformes (Devonian lungfish), started to gulp down air in order to breathe. Later on the ancestors of mammals utilised the olfactory nares (situated above the fish's mouth and used for smell) as nostrils for the function of breathing on land.

In most fishes, the nares function only as entrances to the olfactory organs, there is no connection between them and the mouth, as occurs in mammals. Therefore there is no need for a palate, which in mammals separates the nasal and oral cavities. Fish obtain oxygen for respiration by taking water directly into the mouth and then forcing it back into the pharynx, where it flows across gills located in a series of slits leading from the pharynx to the exterior.

Land based organisms obviously extract oxygen from air instead of from water. To do this they evolved a second major function for the nares that they inherited from their fishy ancestors. While retaining the olfactory function, these openings became the air intake for breathing.

In amphibians—the earliest land vertebrates—air enters the external nares and then passes through the internal nares, which are evolutionarily newer openings, into the front of the oral cavity, from which it moves into the pharynx and then into the trachea. There being no palate, no separate nasal cavity exists in these animals; both the oral cavity and the pharynx are common passages for the digestive and respiratory systems.

In most reptiles and birds, a pair of longitudinal folds in the roof of the oral cavity forms a passage that leads air from the internal nares to the pharynx. Complete separation of nasal and oral cavities by a palate, however, is found only in crocodilians and in mammals. In mammals the bony, hard palate is supplemented posteriorly by a thick, membranous, soft palate.

In the evolution of terrestrial vertebrates, the pharynx has lost the gas-exchanging gills and has become a short passage linking the mouth to the esophagus and the trachea. The esophagus has elongated to join up with the stomach, which now lies within the abdomen. Athough functional, it is this evolutionary adaption that results in the gastrointestinal tract crossing with the respiratory system. The progression of these systems from fish, to amphibian to reptiles to birds and eventually mammals gives us an evolutionary perspective as to why these systems are connected in a somewhat risky way.

Another interesting example of suboptimal design can be seen in the eye, which I will discuss in my next post......... When I find some time.

cofty

That was really interseting, I had never even heard the word nares before.

cantleave

Nares are great! I used to think those little holes were nostrils until I did my A level in biology.

frankiespeakin

I still thinking of dna came about in many cells in the time frame of millions of years so that there is no common ancestry of all dna life forms on this planet(not rulling out that the precusor molecules could have seeded our planet from another planet, mushroom spores can survive the vacuum of space for instance).

Also cross breading in cells with different origens of dna could also have occurred. So I would think that some where down the line one species could have common ansestry with many or all species but that might be millions of years after dna been around. Being that we can't rule out molecular combinations made in outer space from a variety of places inside our galaxy over billions of year before from exploding stars and other life forms on other planets, so that common ancestry could be our entire galaxy, and of coarse everything goes back to the big bang and beyound.

Amelia Ashton

The explanation regarding the larygeal nerve was my tipping point from fantasy to reality. The next one I watched was the Richard Dawkins explanation of the development of the eye and then my de-conversion was complete.

cofty

I still thinking of dna came about in many cells in the time frame of millions of years so that there is no common ancestry of all dna life forms on this planet - Frankie

So why do we all share the same code?

The relationship between the 64 codons and the 20 amino acids does not have to be as it is. Why would it evolve more than once in precisely the same way?

frankiespeakin

Good question. I would think that a common origen would go back further than dna. We are talking time spans of millions of years and a system of life making a series of steps to Dna fileing information with rna readers and builders of protiens. Why should we expect that one system useing DNA took over the rest and dominated our planet with life?

cofty

Why should we expect that one system useing DNA took over the rest and dominated our planet with life?

And yet it did.

The answer of course is natural selection.

It seems certain that RNA was a precursor to a DNA world.

frankiespeakin

Cofty,

The precursors of dna and the whole process of DNA information filing had to have a gradual start not just a one time thing and bam it takes over at least that seems more likely or mathematically more probable.

It may very well be all dna life forms came from a single dna life form but it seem too remote a possiblity in my mind, if I'm proven wrong I don't care I have nothing emotional invested my view and would be interested in what the real answer is what ever it is. Maybe a better computer with higher processing capabilities can give us the answer, alogrithms might show us the answer with reguards to DNA.

The Common Ancestry Thread

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