Evolutionary drawbacks

[Supercommunist]

So I think most of us are aware that evolution is not perfect, and an organism may not develop an extremely useful adaption simply because it did not confer a great reproductive advantage or it simply didn't manifest but I thought it would be intresting if we could discuss animal traits on paper don't seem to have any drawbacks but probably do.


Here are some I am curious about:

Teeth replacement: I honestly don't see any many downsides to this trait and believe the theory as to why most mammals are not capable of replacing their adult teeth is because our ancestors were short-lived insect eaters that never had to worry about that and lost that trait. I have, however, heard some people speculate that polyphyodonts naturally have a more difficult time evolving specalized teeth but I am not sure that's true, given rodents have very specalized teeth and in fact known to die if they let their teeth grow too much.

Thresher shark tail: This one I am super curious about. at first I guessed that the huge fish-killing tail might be somewhat inefficient for movement but when I actually watched footage of them hunting they seem just as mobile as most other active sharks.

Ability to synthesize vitamin c: very obvious advantage, but I wonder if they are any advantages to not being abiity to synthesize viatmin c or if it really is just a flat out drawback.

[Infinity Blade]

My guess is the disadvantage with polyphyodont teeth is that they require more energy for them to be continually replaced. No, I don't think they have a more difficult time evolving specialized teeth. Not only do you have rodent incisors (like you mentioned) as counterexamples, but you also have the upper canines of Thylacosmilus, the molars of elephants, and literally any reptile with ziphodont dentition, really.

[creature386]

Mar 15, 2021 23:02:50 GMT 5 Supercommunist said:

Ability to synthesize vitamin c: very obvious advantage, but I wonder if they are any advantages to not being abiity to synthesize viatmin c or if it really is just a flat out drawback.

I've been wondering about this for a while, too.
I came up with two ad hoc hypotheses:
1. Most mutations are negative, so, genes not protected by selection will degrade naturally over time.
2. There used to be a polygenic mutation that was beneficial for our ancestors over all, but it also resulted in the de-activation of our vitamin C synthesizing genes.
From my research, it seems that there is a third option, namely that vitamin C production has certain costs that our ancestors got rid of:

However, biochemists speculate that there may have been some concurrent advantage of this mutation that caused it to persist and spread in the human lineage. For instance, since one of the products of the reaction catalysed by gulonolactone oxidase is hydrogen peroxide, Halliwell suggested in 2001 that the loss of biosynthesis balanced the "cost" of production, since the advantage of producing one vitamin C molecule would be lost by the production of this reactive oxygen species (Halliwell 2001).

More recently, Grano and De Tullio proposed another hypothesis, based on the studies by Knowles et al. In 2003, Knowles et al. demonstrated that vitamin C regulates a key stress-induced transcription factor called Hypoxia Inducible Factor 1α (HIF1α), a protein that, when activated, regulates the expression of hundreds of stress-related genes. Notably, the activation of HIF1α occurs in the absence of adequate oxygen or vitamin C supply. Grano and De Tullio therefore proposed that organisms that have lost vitamin C biosynthesis have an advantage: they can finely regulate HIF1α activation on the basis of the dietary intake of vitamin C (Grano & De Tullio 2007). When vitamin C supply is sufficient, the HIF transcription factor is less active than in conditions of vitamin C deficiency. In other words, the lack of vitamin C biosynthesis allows our bodies to know more about our nutritional status and consequently set the proper baseline of HIF1α expression. It is like a sensitive titration system.

There is a third yet still unexplored possibility. We know from other studies that pseudogenes are not inert, but can have a significant role in epigenetic control of gene expression (Poliseno et al. 2010). Could this also apply to the human gulonolactone oxidase pseudogene? Time (and much research) will tell.

www.nature.com/scitable/topicpage/the-mystery-of-vitamin-c-14167861/

[theropod]

Mar 15, 2021 23:02:50 GMT 5 Supercommunist said:

So I think most of us are aware that evolution is not perfect, and an organism may not develop an extremely useful adaption simply because it did not confer a great reproductive advantage or it simply didn't manifest but I thought it would be intresting if we could discuss animal traits on paper don't seem to have any drawbacks but probably do.


Here are some I am curious about:

Teeth replacement: I honestly don't see any many downsides to this trait and believe the theory as to why most mammals are not capable of replacing their adult teeth is because our ancestors were short-lived insect eaters that never had to worry about that and lost that trait. I have, however, heard some people speculate that polyphyodonts naturally have a more difficult time evolving specalized teeth but I am not sure that's true, given rodents have very specalized teeth and in fact known to die if they let their teeth grow too much.

Rodent incisors are not replaced, they are merely evergrowing, that is a difference. There are no mammals with true tooth replacement (polyphyodonty), but there are quite a few with rootless teeth (evergrowing incisors or euhypsodont molariforms) that still only represent a single tooth generation (and would not grow back if the whole tooth were lost).

I think the general school of thought is that mammalian dentitions were highly reliant upon precise tooth-on-tooth occlusion (think of carnassials for example, or even our own molars), which would not work in the context of polyphyodont tooth replacement that would result complete loss of occlusal precision with every tooth replacement. But it can work in the context of a single tooth continuously growing, as long as the growth is opposed by wear on the other side, thereby keeping the shape of the tooth constant.
Still, many mammals that have not evolved it would arguably benefit from having this trait, e.g. elephants (which evolved what’s basically pseudo-polyphyodonty, but in a manner most comparable to Hadrosaur dental batteries in that it still results in a sort of continuous replacement of the chewing surfaces, without interruption, similar to euhypsodonty).

But yes, having lost and never really re-evolved the trait of polyphyodonty certainly plays into it. Something like an odontocete for example would certainly benefit from polyphyodonty, but simply has never reaquired the trait.

[Supercommunist]

Rodent incisors are not replaced, they are merely evergrowing, that is a difference. There are no mammals with true tooth replacement (polyphyodonty), but there are quite a few with rootless teeth (evergrowing incisors or euhypsodont molariforms) that still only represent a single tooth generation (and would not grow back if the whole tooth were lost).

Not even any extinct mammals? Somebody online told we there were a few mammals that could replace their teeth and I took their word for it lol.

My guess is the disadvantage with polyphyodont teeth is that they require more energy for them to be continually replaced.

Yeah that is certainly true, but I imagine the energy loss is so small it is hardly a disadvantage. I think one huge drawback of being unable to grow teeth back is dramatically reduced lifespan.

Most big cats and other mammalian carnviores start facing severe dental issues by age 8-10 and I don't think its a concidence that mammalian carnivores don't live past 20.

Also here's another trait that doesn't seem to have a drawback at first glance:



Being able to store lots of your food in mouth seems pretty nifty to me.

[Infinity Blade]

Yeah, I definitely don't think the energy going into tooth replacement is huge either.

I think the general school of thought is that mammalian dentitions were highly reliant upon precise tooth-on-tooth occlusion (think of carnassials for example, or even our own molars), which would not work in the context of polyphyodont tooth replacement that would result complete loss of occlusal precision with every tooth replacement. But it can work in the context of a single tooth continuously growing, as long as the growth is opposed by wear on the other side, thereby keeping the shape of the tooth constant.

Pakasuchus had dental occlusal complexity rivaling that seen in mammals. And notosuchians appear to have had the ability to replace their teeth à la the vast majority of toothed reptiles (I say the "vast majority" because I can name one exception). I assume, then, that Pakasuchus could replace its teeth too.

Pakasuchus is unique among crocodyliforms, including the dentally diverse notosuchians, in having fully complementary upper and lower molariform cheek-teeth (Fig. 2c–j). The crown on both upper and lower molariforms has two parallel, rostrocaudally oriented crests separated by a longitudinal trough (Fig. 2d, g). This degree of complementary occlusal morphology maximizes crown–crown contact, providing two shearing edges separated by a trough for processing food. Importantly, microcomputed tomography (microCT) of unerupted molariform tooth crowns reveals that the complex trough crest morphology observed in the working dentition is primary in nature and not the result of wear (Supplementary Fig. 3). The complex morphology and high degree of occlusal precision of the cheek teeth in Pakasuchus shows a level of sophistication otherwise seen only in mammals.

www.nature.com/articles/nature09061

[Supercommunist]

I am sure you guys have heard of the pterosaur with thumbs:



What drawbacks do you see that having on a pterosaur if at all? Think it it would be possible for the larger pterosaurs to evolve them without hampering their ability to fly?

[Supercommunist]

Photosynthetic animals are neat:



Wonder what are the drawbacks of being able to get energy from sunlight.

en.wikipedia.org/wiki/Elysia_chlorotica

[Supercommunist]

Hey guys you remember on CF how a lot of people made the claim that animals with sweat glands have thinner skin that is more vunerable to clawing?

I'd like to discuss that on CF. IIRC the idea gained a lot of traction when gato gordo posted some excerpt about pannaculum carnaseum:

Wounds heal more rapidly by contraction, which does not require creation of new tissue. Contraction is most efficient in mammals having a subcutaneous muscle called pannaculum carnaseum, which allows animals to move their skin.

The skin in areas without pannaculum carnaseum underneath is not mobile, and thus it is firmly attached to inner structures. Therefore, the degree of mobility or attachment of the skin in different species depends on how developed is the pannaculum carnaseum.

The pannaculum carnaseum is well developed and covers large body areas (the whole trunk) in all carnivore predators (felines, canines, hyenas, bears, etc), in rodents, lagomorphs (rabbits/hares), horses, camels, bovids, pigs. However, it is much reduced in primates and is almost absent (vestigial) in big apes and humans.

Thing is the first thing that comes up when you google pannaculum carnaseum is CF itself.

There is something called the panniculus carnosus:
onlinelibrary.wiley.com/doi/10.1111/joa.12840

But, I don't think they are the same thing.

I am not totally willing to throw out the idea that sweat glands make animals more vunerable to claw wounds as equines, another animal that can sweat, seem very suspectible to clawing:





Of course this vulnerability may simply be due to the fact that they have thin skin.

good-horse.com/health-management/horses-really-thick-skin/

[Infinity Blade]

Could panniculus carnosus be an alternate spelling/terminology for that muscle? But gotta love how "pannaculum carnaseum" gets like, two pages of Google results, all of which are on some kind of discussion page about animals fighting each other.

It does kind of raise eyebrows that the only two groups of animals I've ever heard of being straight-up disemboweled by big cat claws are apes (I think there was one of a leopard gutting a gorilla?) and equines, both of which sweat extensively to cool themselves, and neither of which are particularly thick-skinned.

[Supercommunist]

Hippos don't sweat in a traditional sense but they do produce "blood sweat" and an episode of inside nature's giant empathized how incredibly tough and thick hippo hide so at the very least, the secretion of fluids through the skin does not necessarily translate to thin and delicate skin.

On the otherhand, another case that bolsters the idea is that pretty infamous case of a man getting scalped by a leopard's paw swipe.

[elosha11]

Mar 15, 2021 23:02:50 GMT 5 Supercommunist said:

So I think most of us are aware that evolution is not perfect, and an organism may not develop an extremely useful adaption simply because it did not confer a great reproductive advantage or it simply didn't manifest but I thought it would be intresting if we could discuss animal traits on paper don't seem to have any drawbacks but probably do.


Here are some I am curious about:

Teeth replacement: I honestly don't see any many downsides to this trait and believe the theory as to why most mammals are not capable of replacing their adult teeth is because our ancestors were short-lived insect eaters that never had to worry about that and lost that trait. I have, however, heard some people speculate that polyphyodonts naturally have a more difficult time evolving specalized teeth but I am not sure that's true, given rodents have very specalized teeth and in fact known to die if they let their teeth grow too much.

Thresher shark tail: This one I am super curious about. at first I guessed that the huge fish-killing tail might be somewhat inefficient for movement but when I actually watched footage of them hunting they seem just as mobile as most other active sharks.

Ability to synthesize vitamin c: very obvious advantage, but I wonder if they are any advantages to not being abiity to synthesize viatmin c or if it really is just a flat out drawback.

Despite their seemingly less than streamlined tail, Thresher sharks seem to share the lamid sharks' general athleticism. They are probably not as nearly as fast as a mako or salmon shark but they might rival a great white at around 20 to 30 miles per hour.

[Supercommunist]

Anybody know if they are any notable downsides to having spiracles.

I can't help but thinking that ram ventilation has some very obvious drawbacks.

en.wikipedia.org/wiki/Spiracle_(vertebrates)

[Supercommunist]

Thoughts on lobed feet like those on coots?



I am guessing they are better than web feet on land but worse in water.