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Crabs evolved at least five times from separate groups of crustaceans (2021)

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Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#71

Post by BbzzbB »

asfarley wrote: post #58
alanbernstein wrote: post #48

Earlier quoted context omitted.

So there are 0) aquatic animals, 1) land animals (evolved from 0), and 2) aquatic mammals (evolved from 1). You want to know if there are e.g. 3) land animals that evolved from aquatic mammals? Not that it isn't an interesting question, but what exactly would this tell us?

It might suggest the existence of loops in the evolutionary tree, making it more of a general graph.

The evolutionary tree, maybe more accurately the phylogenetic tree, wouldn't loop as it is derived from genetics in modern times. Our ancestors' attempts at making evolutionary trees from morphology (can't fault them for not sequencing DNA) have got a lot of things wrong because seemingly relating creatures were not at all. Convergent evolution being a major reason for stuff they got wrong, making morphology a poor approximation of phylogeny.

Even if 2 distinct species eons apart ended up literally identical and sexually compatible thru some cosmic luck, they wouldn't show up as a loop since we could tell how far apart they are by looking at how mutated some useless and asexually transmitted gene is (mitochondria DNA provides that for eukaryotes, say cytochrome oxidase I gene). The key part is that the gene doesn't receive any evolutionary pressure, so that it only drifts thru random mutations (considering they can't provide a reproductive advantage/increase "fitness"). If you know the mutation rate (which we do), you can date how far back a common ancestor goes between two species' by basically running a diff script on their COI gene sequences.

Considering every known form of life descends from a single ancestor (LUCA [1]), a tree (or root system) analogy is quite apt.

1: https://en.wikipedia.org/wiki/Last_universal_common_ancestor

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#72

Post by Scarblac »

throwaway742 wrote: post #70
gibolt wrote: post #17

Earlier quoted context omitted.

The teeth are already there. A few gradually longer ones makes obvious sense to be a better predator, giving them an evolutionary advantage.

Then why aren't they still around? Why don't they evolve again?

Saber tooth tigers and humans coexisted for a while, and the tigers were probably very dangerous to us. That and having to adapt to the end of the ice age, I don't think we know what was the bigger factor.

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#73

Post by aasasd »

astrange wrote: post #33
TedDoesntTalk wrote: post #29

Earlier quoted context omitted.

> misunderstanding of their culture Maybe it’s just your culture?

This reminds me of ESR's Jargon File, which kept defining "hackers" as liking or doing things when it was actually just him.

As the other dude said, ESR only maintained the file after it was abandoned or something.

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#75

Post by throwaway894345 »

animal_spirits wrote: post #40
kjeetgill wrote: post #14

Eons did a great piece on this recently: https://youtu.be/wvfR3XLXPvw One of the things I love about the way Eons cover topics is how they don't just focus on what we know, but also how we know, who figured things out, and what we got wrong along the way. Can't endorse their style of science journalism enough.

PBS has been putting out such great content in the last 5 years. Really impressive and highly overlooked

I haven’t seen Eons. I’ve felt like the quality on Nova and Nature has slipped though. Glad other programs are picking up the slack.

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#76

Post by throwaway894345 »

pratik661 wrote: post #37

Ive always wondered this: has a species have an evolutionary history where they originated in land but adapted to living in water and then adapted to living on land again?

Whales have the opposite—evolved in water, came to land, then evolved back for the water.

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#77

Post by zdragnar »

ativzzz wrote: post #63
mirekrusin wrote: post #61

Earlier quoted context omitted.

I wasn't aware of that some time ago, it's a fascinating insight. I got a lightbulb (going wtf/dark actually!) when watching cartoon or something with triceratops. They looked so much like rhinos. But had eggs. I had trouble reconciling it with evolution. They were so far ancestor-wise but so close physically-looking wise. Convergent evolution is very interesting. It suggests aliens may not be that different from us…

> It suggests aliens may not be that different from us after all, if exist. Alternatively, they are the more evolutionally convergent species and we will evolve towards something inhuman

All of this has happened before before.

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#78

Post by me_me_mu_mu »

version_five wrote: post #21
samatman wrote: post #15

Even more wild to me is that saber-toothed cat-like predators evolved seven separate times: https://en.wikipedia.org/wiki/Saber-toothed_predator

There was a recent article on here about how species that looked alike were not necessarily related and is was more common to have physically dissimilar but geographically close species that were evolutionary relatives. One of the points was that convergent evolution was more common than people thought. These stories appear to support the convergent evolution assertion

Curious if that applies to humans as well. I’m from S Asia and well.. I do have my distinct looks that I share with my family and community, that are different from other communities. Are humans like that as well? I am aware of the migration theories and people crossing ice bridges and all that, but did people evolve in different areas and then spread out after settling their original area?

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#79

Post by dEnigma »

micro_cam wrote: post #69
pratik661 wrote: post #37

Ive always wondered this: has a species have an evolutionary history where they originated in land but adapted to living in water and then adapted to living on land again?

The Hawaiian nene goose has become mostly terrestrial and is loosing its webbing.

The Cape Barren goose also rarely swims, according to Wikipedia.

https://en.wikipedia.org/wiki/Cape_Barren_goose

Re: Crabs evolved at least five times from separate groups of crustaceans (2021)

#80

Post by graycat »

mirekrusin wrote: post #61
version_five wrote: post #21

Earlier quoted context omitted.

There was a recent article on here about how species that looked alike were not necessarily related and is was more common to have physically dissimilar but geographically close species that were evolutionary relatives. One of the points was that convergent evolution was more common than people thought. These stories appear to support the convergent evolution assertion

I wasn't aware of that some time ago, it's a fascinating insight. I got a lightbulb (going wtf/dark actually!) when watching cartoon or something with triceratops. They looked so much like rhinos. But had eggs. I had trouble reconciling it with evolution. They were so far ancestor-wise but so close physically-looking wise. Convergent evolution is very interesting. It suggests aliens may not be that different from us…

My understanding is that eggs and no-eggs are not as different as might be expected. After all, the no-eggs still have eggs but, just, don't lay the eggs or let us make French toast, custards, or omelets! Maybe a key issue would be the amazing placenta. But maybe the egg animals are not so far from having a placenta because they still DO have to be willing to accept the male sperm without killing it, and part of what is amazing about a placenta is that it lets the foreign tissue of the baby exist and thrive in the womb of the mother without destroying it as foreign tissue -- in part, tolerating the sperm, the egg animals already have to do that. These are some details the hookup culture will want to use as sources of conversation? Maybe?
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