Re: Why all apes including humans do not have tails

On 29/02/2024 16:06, erik simpson wrote:

On 2/29/24 4:29 AM, FromTheRafters wrote:

It happens that RonO formulated :

On 2/28/2024 5:41 PM, erik simpson wrote:

On 2/28/24 3:21 PM, RonO wrote:

It turns out that the common ancestor that between gibbons and the great apes had an ALU transposon jump into the intron between exon 6 and exon 7 of the TBXT gene.  There was already an transposon between exon 5 and exon 6.  Monkeys and apes have the ALU insertion in the intron between exon 5 and exon 6, but the apes have the second ALU insertion in the intron between exons 6 and 7.  So it turns out that apes still have the exon 6 sequence in the TBXT gene, but the two ALU transposon sequences form a stem loop structure in the RNA transcript that messes up processing so exon 6 is skipped and exon 5 is stuck to exon 7 in the final ape mRNA.  So part of what makes us human is due to a transposon insertion mutation into the TBXT gene.
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The insertion happened in the common ancestor of all extant apes, and has been retained by the extant ape lineages.
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https://www.nature.com/articles/s41586-024-07095-8
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The article is open access.
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Ron Okimoto
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Another effect of this modification is also "Moreover, mice expressing the exon-skipped Tbxt isoform develop neural tube defects, a condition that affects approximately 1 in 1,000 neonates in humans10. Thus, tail-loss evolution may have been associated with an adaptive cost of the potential for neural tube defects, which continue to affect human health today."
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Evidently, the advantages of losing the tail outweigh the disadvantage of the neural tube defects.
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What were the advantages?
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Some other simian lineages have lost their tails, but what is the advantage?
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Apes did become brachiators, but other simian lineages did not, and some simian lineages that adopted a similar lifestyle for supporting themselves in the trees, actually developed prehensile tails as a fifth limb for supporting themselves hanging from branches.
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For birds there was a selective advantage in terms of weight, and the tailbones degenerated and fused into a small nub.  The tail was not lost, and birds still have a nub that they call a pygostyle that still supports the muscles that control the tail movements and so the feathers associated with the tail.
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Ron Okimoto

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I suppose sitting is much easier without a tail.
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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6417348/
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That can't be it.  My dog has a long tail and has no trouble sitting.

A dog can adjust their tail.  The article refers
to a Young man who had one and didn't know what
to do with it, and who indeed was having trouble
sitting with comfort.
I can't read this style of writing well enough
to tell whether doctors removed the tail, or
only adjusted the bones that it was attached to.