But are they there for a reason?
One of my earlier blogs dealt with organs that were absent in some organisms even though we would have expected them to be present: take the absence of red blood in some fish or the lack of lungs in some salamanders. This blog is about organs termed ‘useless’ and I was thinking of them in my dentist’s chair, while he was giving one of my wisdom teeth a root canal treatment. Wisdom teeth in humans are sometimes called useless, because the relatively small jaw of humans no longer has the space for the wisdom teeth (is one opinion). But in my case, all 4 wisdom teeth are in good shape and I use them. Another human organ often referred to as useless is the appendix and we can certainly survive without it very well. Some people would include the foreskin of us males. But useless? The appendix is thought to have a function as a reservoir for good gut bacteria and the foreskin is a protective cover. Therefore, both cannot be deemed to be totally useless. However, I’d say the nipples on the chest of boys and men are indeed “useless”, not possessing any particular function that I can imagine.
Some organs regarded as useless are vestigial structures; structures so to speak that are on their “way out”; structures that once did have a function, but owing to the tenet of the survival of the fittest, lose all their importance and remain around for generations as a genetic burden. I’d say the beard of us male subjects is such a useless structure (although it can look elegant and give a person an aristocratic appearance, but more often than not, it looks untidy and unkempt). For postmenopausal women, I wonder what biological use their breasts still have, when child-bearing has ceased and milk production is out of the question. Why don’t the breasts diminish or contract? Or is their presence somehow linked to the female’s greater longevity than that of men even if they no longer are capable of producing milk?
As a New Zealander, it has always puzzled me why the Kiwi bird has these tiny wing bones when there are not even vestiges of the wings or why the native New Zealand frogs apparently have tail-wagging muscles when there are no tails to wag? I have also wondered why certain diurnally active firefly species still have light organs (although the latter are actually much reduced by comparison with those of the nocturnal firefly species). And what about the hind leg bones in whales, the pelvic bones in some snakes: useless because there are no hind legs. Or is there still an unknown role for them in balancing the body?
I think one of the best examples of a pretty useless structure are the puny front legs (let’s call them arms) of the fierce and predatory Tyrannosaurus rex. They may have been almost a metre long and moved by powerful muscles, but in relation to the rest of the body of T. rex they were tiny. Obviously the arms represent severely reduced front legs with a strongly reduced number of fingers: two large digits with sickle-shaped claws are present and a tiny vestigial third finger may be present. It seems accepted that the massive head of T. rex and its enormously powerful bite have required a trade-off between muscles to support the head and the jaws of the beast and muscles to support the forelimbs. Since head and jaw were far more important than the forelimbs, i.e. the arms, they missed out and became vestigial. However, as to the function of the arms, no consensus has been reached so far.
That they could have assisted to hold a partner during courtship is one idea, because in order to use these arms, the object or subject to use them with had to be very close indeed. Another idea, also requiring close proximity, is that the arms and their claws could have helped to rip into prey reducing its struggle and holding it like meat-hooks hold a carcass. It is also possible that the small arms could have assisted a T. rex to rise up from the ground once it fell down, perhaps in a struggle with prey or another T. rex individual, or when getting off the ground after a nap. For the time being the arms of T. rex remain a mystery, but it’s nice they are there, for that gives us something to speculate.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2020.
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