Crabs evolved at least five times from separate groups of crustaceans (2021)
newsweek.com
newsweek.com
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.
The interesting part about it is whether they represent a local minima that optimization gets stuck in - i.e. the returns on building yourself an exoskeleton keep increasing the more exoskeleton you add, so once you chance onto that path every other direction then "more exoskeleton" is a net negative for the next generation.
"Whatever the advantages are, they do not apply in all habitats because some groups have also lost carcinization; one modern example being the frog crab."
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 after all, if exist.
Alternatively, they are the more evolutionally convergent species and we will evolve towards something inhuman
Characters in the show are frequently forced to confront situations in terms of either coincidence, synchronicity or divine intervention.
The quote underlines a recurring theme in the show and how people adapt to it (though later on gets rather heavy handed).
What was striking to me was how far in ancestry chain you have to go back with rhinos to meet common ancestor with egg-lying triceratops - this ancestor will not look like any of them, however they did meet from completely divergent dna to be so look alike, crazy.
Pigs, rhinos, hippos, ..., triceratops all look much the same to me!
Hmm ...? Would the real test of sameness be to see if they make similar BBQ???
Edit: dropped word
I'd argue that rats are exceptionally close to humans (both are mammals). Similarly other potential candidates: raccoons, bear, possibly dolphins or other cetaceans.
Insect, plant, or colonial intelligences would be interesting.
"They found that the animals grouped together by molecular trees lived more closely together geographically than the animals grouped using the morphological trees."
There might be some others such as lactose tolerance that are less obvious.
Another possible explanation (speculation) is that they met and mixed with yet undiscovered hominid species.
Several things have changed as recently as 11,000 years. “Examples for adaptations related to agriculture and animal domestication include East Asian types of ADH1B associated with rice domestication,[71] and lactase persistence.” https://en.wikipedia.org/wiki/Recent_human_evolution
[0] https://royalsocietypublishing.org/doi/10.1098/rstb.2018.023...
What can they actually discover? 10 legs good? But how about 12? [1]
> The crab with the longest legs is the Japanese spider crab. It’s not related to spiders, despite its name. When extended, its legs can be as long as 12 feet.
Now there's a nightmare for you.
[1] https://www.reference.com/pets-animals/many-legs-crab-4c30fb...
"Whatever the advantages are, they do not apply in all habitats because some groups have also lost carcinization; one modern example being the frog crab."
- Photosynthesis created and maintains the current composition of the athmosphere. By removing too much CO2, it likely also contributed to several ice ages.
- Early life sequestered almost all the iron in the primordial Earth's sea into sediments, which turned into iron ores.
- We take the presence of such a basic thing as soil for almost granted, yet soil is created and maintained by life itself. At the same time, soil is only absent in environments where only extremophiles can survive. From this follows that it must have taken a lot of time for life to conquer the land and make it hospitable by creating a soil covering.
From these things, I (perhaps hastily) conclude that planets with life could actually look a lot like Earth. Or they can at least be recognized by the presence of chemically and physically unlikely features such as reactive elements like oxygen in their athmospheres.
The point is that plants are capable of terraforming the planet on their own. It isn't even a slow process if humans help the plants do their job.
> It is believed that modern-day whales evolved from land-based animals about 55 million years ago. These land-based mammals are believed to be hoofed mammals, sharing a common ancestry with even-toed ungulates such as the cow and the deer.
> Evolution of Whales Whales started their journey as all other organisms have, as single-celled bacteria.
An evolutionary picture of the whales can be broken down as follows:
- 3.8 billion years ago: The first single-celled organisms appeared (Bacteria)
- 3 billion years ago: Viruses (also single-celled organisms) became present
- 2 billion years ago: Eukaryotic cells are present. These are cells that contain organelles, or tiny organ-like structures
- 1.5 billion years ago: Eukaryotic cells evolved three ways. These cells evolved into the ancestors of plants, animals, and fungi
- 900 million years ago: The first multicellular structures became present
- 800 million years ago: The animal strain of organisms undergoes its first split and continues into basic marine organisms such as sponges
- 540 million years ago: The first chordates or animals with backbones are present
- 530 million years ago: The first true vertebrate or boned organism is present
- 500 million years ago: Animals first started exploring the land
- 417 million years ago: Lungfish became present. Lungfish are the first organisms to breathe both on land and in the water with both lungs and gills
- 397 million years ago: The first tetrapods or four-legged species are present
- 340 million years ago: Amphibians branch off from the other tetrapods
- 310 million years ago: The remaining tetrapods split into what will be reptiles, birds and dinosaurs, and mammals
- 200 million years ago: A mass extinction occurred and warm-blooded proto-mammals developed
- 140 million years ago: Placental mammals also known as eutherians are present
- 105-85 million years ago: The placental mammals split into four major groups, including laurasiatheres, which will contain the whale species.
- 65 million years ago: The greatest extinction event so far wipes out the dinosaurs providing more potential for mammals to colonize the planet
- 50 million years ago: Artiodactyls pakicitus, a mammal, resembling a wolf and tapir mix with cloven hooves begins evolving into what we know as whales
- 47 million years ago: Early forms of whales live in shallow seas, returning to land to mate and give birth
- 35-45 million years ago: The first fully aquatic whale is present (Basilosaurus)
Modern-day whales are believed to have moved into the oceans around the Tethys Sea, now the Mediterranean Sea and Asia.
Here's the general group people seem to be fairly sure led to hippos; the ones that led to whales might have been an earlier group that gave rise to this group, or perhaps one of these, or perhaps not all whales share a 'root whale':
https://animals.fandom.com/wiki/Anthracotheriidae
The actual kind of data they use to make these judgements is mostly bone fragments from fossils, as comparing modern DNA of hippos and whales can only tell you so much. Here's an example study from 2003 on the hippo lineage:
https://wp.ufpel.edu.br/cdrehmer/files/2017/06/hipopotamo-ST...
http://www.onezoom.org/life/@Hippopotamidae=510764?img=best_...
https://en.m.wikipedia.org/wiki/Pakicetus
> the closest living non-cetacean relative being the hippopotamus.
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?
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
- ring species
- species complexes
- hybrid species (turning the tree into a Directed Acyclic Graph)
- horizontal gene transfer via plasmids (between bacteria) or viruses
(edited for formatting)
https://en.m.wikipedia.org/wiki/Comparative_foot_morphology
> The paw of the dog, the hoof of the horse, the manus (forefoot) and pes (hindfoot) of the elephant, and the foot of the human all share some common features of structure, organization and function.
That's not how evolution works. Survival of the fittest isn't about aspiration. It's what's left when the fittest are left standing.
This means also that with enough data about other planets we could even made a raw guess the shape of creatures that could live there.
We've changed the silly title (edit: I meant the article's own linkbaity title) to a more interesting sentence from the article body.
"Scientists are puzzled!, Scientists don't know why!, Scientists pull out their moustaches by frustration!"
(What scientists really say):
"Evolution, duh..., nice one, where is my coffee?, sip, sip, show me the pleopods"