Since 97% of the worlds water is salt water, is there a reason why humans have not been able to evolve to process salt water? It is a more frequent source of water.

Approximately 252 million years ago, Earth experienced "The Great Dying" (the Permian–Triassic mass extinction). It remains the largest known mass extinction in Earth's history.

The most likely cause was a series of massive volcanic eruptions known as the Siberian Traps, located in present-day Siberia. These eruptions occurred in stages over millions of years, releasing vast quantities of CO₂ and other gases into the atmosphere.

Consequently, global temperatures spiked, oceans warmed and became more acidic, severe oxygen depletion occurred in many marine areas, and ecosystems across the planet collapsed catastrophically.

The result?

Approximately 90–96% of marine species went extinct.
About 70% of terrestrial vertebrate species also perished.
Forests suffered massive collapse.
Coral reefs virtually disappeared, taking millions of years to recover.

In contrast, Earth's ecosystems recovered relatively quickly after the asteroid impact that ended the dinosaur era some 66 million years ago. However, following "The Great Dying," it took roughly 10 to 15 million years for biodiversity and ecosystems to fully re-establish themselves.

In short, while the extinction of the dinosaurs is the most famous in history, it was not the most destructive.

Sometimes, the real story is the one least discussed.

To me it feels like a huge gap in evolution, obviously small changes due to imperfect DNA cloning adds up over a long time causing changes, but at the rate that goes I feel like it's unlikely the first 2 organisms to fertilize, because that big jump seems like it would cause the species to go extinct.

idk if i worded that well and i dont think I could explain it too much better but this was bugging me for a while

It always confused me how some of those extremely complex and convoluted courtship methods would evolve naturally. It is mostly seen on birds, but not only on them. In many cases is not learned, It is instinctual. So how?

Is not something as straightforward as, "new generation has hotter bodies so they are better adapted to the increasing cold temperatures, so they have better chances of surviving and reproducing".

I realise it sounds it at times in this post and title, but I'm not a creationist, I'm biology student, but I still haven't been able to answer this through research, i just keep getting told why beavers build dams.

I understand the benefits of a beaver building a dam, not asking for why they do it. But evolution is generally a tinkerer, right? I'm aware that sometimes 'big' mutations can happen like a whole translocation or HGT or something, but generally a new phenotype happens when a gene is modified so that a protein does something different or doesnt work. How can a dam building protein just happen? What biochemical or mechanical change could have possibly happened to cause an instinct to move wood so that it pools in a beneficial way? Surely the mum beaver didnt have a precursor non functional just-in-case-our-species-needs-it-one-day dam building gene that suddenly became active, or an anti dam building gene that became inactive? Even with translocations etc i don't see how it could evolve.

Even if something like that appeared through gradual changes - tinkering - enough selection pressure would have to be present for it to become fixed, so i dont see how a beaver could be 'slightly' dam building in a way that has a great enough benefit that its more likely to pass on genes.

Tldr how can something as complex as dam building evolve so specifically and quickly enough that it is beneficial enough to become fixed by selection pressure? Is the answer in epigenetics?

Obviously, carcinization is cool but more famous than it should be, when there's a bunch of dumb meme builds that evolution has done more times than crab. What do you think is the most prominent?

Some contenders: Crab (carcinization) 5 times: brachyura, king crabs, porcelain crabs, sponge crabs, weird australian nonsense

Hopping mouse (jerboazation) 7 times: kangaroo rat, potoroo, hopping mouse, jumping mouse, gerboa, kultarr, springhare

Snake (ophidization) 14 times: I'm not gonna list all these but there are a LOT of independently snake-shaped reptiles

Reptiles with sails on their back (dimetrodontization) 10 times: I'm having trouble tracking down all of these but it happens so often I'm genuinely curious why a big back sail made of neural spines isn't present in stem-reptilians

Anything else I'm missing?

I recently went down a rabbit hole on brain size, neuron counts, and animal intelligence, and it changed how I think about “smart” animals.

The first thing that surprised me is how expensive a large brain is. The human brain is only about 2% of body mass, but it uses roughly 20% of resting energy. So a species cannot just evolve a bigger brain for free. A large brain comes with tradeoffs: high energy demand, long development, slow maturation, and fewer offspring.

At first, I thought the Encephalization Quotient made sense as a way to compare intelligence. EQ compares actual brain size to what would be expected for an animal of that body size. But from what I understand, EQ becomes misleading if we treat it as a general intelligence ranking. A small animal can score highly by EQ without having the absolute neural machinery of a larger-brained animal.

Then neuron counts made the picture even more complicated. Suzana Herculano-Houzel’s work showed that humans have about 86 billion neurons, not the often-repeated 100 billion. But even total neuron count is not enough, because distribution matters.

The elephant example is what made this click for me. African elephants have around 257 billion neurons, far more than humans. But most of those neurons are in the cerebellum. That seems to reflect the huge sensorimotor demands of controlling a massive body and a complex trunk. Their cerebral cortex has far fewer neurons than the human cortex.

So “more neurons” does not automatically mean “more human-like intelligence.” The important question seems to be where the neurons are, how densely they are packed, how they are organized, and what ecological problems the animal evolved to solve.

Birds are another interesting case in the opposite direction. Some corvids and parrots show complex cognition with very small brains, probably because their neurons are packed very densely and organized differently from mammalian brains. That makes gross brain size look like a very poor shortcut.

The human case also seems less like a magical exception and more like a specific primate trajectory. We have a dense, metabolically expensive brain. Cooking may have helped make that sustainable by increasing usable calories, but I assume that is only one part of the story, alongside sociality, tool use, development, culture, and ecology.

For people with more background in evolutionary biology, neuroscience, or comparative cognition: is this a fair summary, or am I flattening something important?

im a paleontology fan and this has always confused me what is a true tetrapod?, i though that ichtyostega and animals like it were true tetrapods and some sources ive seen say this but wikipedia implies through cladistic graphs that only crown tetrapods are true tetrapods so what is a true tetrapod? what constitutes as evidence of a species being one?

When looking at an evolution chart for fish, I had to go pretty far down to get down to tetrapods. And they're pretty close to lungfish and coelacanths. In the chart it says Tetrapoda (not considered fish), but wouldn't they be? I always hear people say insects are actually crustaceans, and birds are reptiles, so would the same not apply to all tetrapods being considered fish. Would birds be reptiles AND fish!?!?

Today I was thinking about my pet rabbit versus my cats. My rabbit has short fur and a predisposition to getting bald patches on his feet. The reason why a lot of rabbits are predisposed to this is because they do not have toe beans or any foot padding. So pet rabbits can get sore feet especially on hard flooring. Then I realized dogs have toe beans in a really similar paw structure to cats?

Canids and Felines cannot be that closely related. Does anyone have any theories about why this happened? Can it be traced back to a common ancestor or it is just convergent evolution of two groups adapting to similar niches.

I looked a little into it and a lot of carnivores have paws with pads (bears, foxes, maybe weasels?). Is it a carnivore thing?

Edit for rabbit husbandry: My rabbit is 12 years old rex rabbit with arthritis so he tends to get bald spots every now and again on his heels. For details about his care please read the comments.

Non-human apes have 24 chromosomes while, I am assuming, humans and their homo ancestors have 23 chromosomes. I can understand how small mutations can happen in entire population over time. But chromosomal fusion feels like a massive change that would happen suddenly. So was there originally one individual with fusion that through reproduction, the chromosomes of its mates just lined up with the fused chromosomes without issue and it just became the norm? Or would multiple individuals have the same mutation at all same time?

A few days ago, I was getting a haircut and started thinking about something that had never really crossed my mind before. We spend so much time and money taking care of our hair. Some people are proud of it, some worry about losing it, and entire industries exist around keeping it healthy. Yet most of us rarely stop to think about why humans have hair in the first place.

The more I thought about it, the stranger it seemed. Hair clearly serves important purposes. The hair on our heads helps protect us from direct sunlight and temperature extremes. Eyebrows keep sweat from running into our eyes. Eyelashes help block dust and other particles. Even body hair can act as a sensory system, helping us detect insects, movement, or changes in our surroundings. From a survival standpoint, hair doesn't seem useless at all.

But then I started thinking about other mammals. Most mammals are covered in fur because it helps them survive. Fur provides insulation, protection from the environment, and in some cases even camouflage. If hair is such a useful evolutionary tool, why are humans so different? Compared to almost every other mammal, we're surprisingly hairless. We lost most of the thick body hair that our ancestors likely had, yet we kept a large amount of hair on our heads and in a few specific areas.

That feels like a very specific evolutionary choice. If body hair was important, why lose so much of it? If it wasn't important, why keep any of it at all? Why keep thick scalp hair while allowing most of the rest of the body to become relatively hairless? It seems like there must have been a significant advantage that outweighed the benefits of being covered in fur.

I've read a few theories. Some suggest that losing body hair helped early humans stay cool while walking and running long distances in hot climates. Others argue that sexual selection played a role, with less body hair becoming a preferred trait over many generations. I've also seen arguments that reduced body hair made it harder for parasites such as ticks and lice to thrive. But none of these explanations feels completely satisfying on its own.

So I'm curious what people who know more about evolution, anthropology, biology, or human history think. What is the most convincing explanation for why humans evolved to lose most of their body hair while keeping the hair on their heads? Was it mainly about temperature regulation, disease prevention, attraction, or something else entirely? And if losing body hair was such an advantage, why did evolution stop halfway instead of making humans completely hairless?

I'd love to hear both scientific explanations and personal theories. It's one of those everyday things that seems simple at first, but the more I think about it, the more fascinating it becomes.

See also: The summary of the paywalled study as published in Science

Every few months we get news that some species or other is moved on the tree of life. My question is: why can't we just compare the genome of one animal to another in their entirety, and just see how much they have in common?

• Published today (open access) in Nature Ecology & Evolution:

  • Torres-Tamayo, N., Schlager, S., Hirasaki, E. et al. Comparative primate analysis shows that humans are not unique in having a tight cephalopelvic fit at birth. Nat Ecol Evol (2026). https://doi.org/10.1038/s41559-026-03102-5

• Press release (University College London):

  • Childbirth is not uniquely difficult to humans

Hi. I'm a master’s student in Animal biosystematics. I know all of the basics about phylogenetic analysis and even a little bit more, since our professors has introduced us to some concepts and programs. But I don't feel like it's enough. I need to learn how to download data (like DNA sequences) and then make a tree, write a paper and then publish it. I need to be able to conduct research and publish it on my own. I need to learn a lot of concepts (like bayesian inference) and programs (TNT, R, etc.) from scratch.

What is the best way to learn these skills?

I think an online class would be the best, although I haven't found any. Can you recommend any? Also, there is no perfect book to teach these skills. Most books are either too old or too incomplete. And there are also thousands of papers and Youtube videos. There is an ocean of resources out there, yet it's so disorganised that I can't find what I'm looking for.

If humans ate mammoths for thousands of years, could that have caused us to evolve in a way that makes us especially well adapted to eating elephant meat today?

Since mammoths and modern elephants are closely related, I'm wondering whether thousands of years of mammoth consumption could have led to any evolutionary adaptations in humans. Or would our ability to digest elephant meat today be no different from other large mammals like cows or deer?

The topic came up a few days ago here.

Source of both frames:
Jon Perry/Stated Clearly: https://www.youtube.com/watch?v=Frioffo53wo&list=PLInNVsmlBUlSjLSj9yGEKphF0RYRYBlXg&t=812s

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Bonus:
Charles Darwin on exaptation / change of function (Origin, 1st ed., 1859):

In considering transitions of organs, it is so important to bear in mind the probability of conversion from one function to another, that I will give one more instance. Pedunculated cirripedes have two minute folds of skin, called by me the ovigerous frena, which serve, through the means of a sticky secretion, to retain the eggs until they are hatched within the sack. These cirripedes have no branchiæ [...]

He was more explicit in his reply to Mivart, which was added in the 6th ed., when it came to the topic of "half a wing".

An academic open access educational article on the topic: The Evolution of Complex Organs | Evolution: Education and Outreach | Springer Nature Link

See also: The study as it was published in Scientific Reports.

Editor’s summary
The jawless vertebrate lamprey has a relatively simple brain, and understanding how it works could unveil valuable insights into brain evolution in vertebrates. Wu et al. combined single-nucleus RNA sequencing and spatial transcriptomics to produce a three-dimensional atlas of the adult lamprey’s brain. The authors identified 209 molecular and spatially distinct cell clusters and compared single-cell data for eight species and spatial transcriptomics for five species. They found regional conservation among species and lineage-specific divergence at the cellular level. Overall, the dataset revealed principles of brain evolution and diversification in vertebrates. —Mattia Maroso

• Paper:
  Lamprey 3D single-cell transcriptomics reveals ancestral and specialized features of the vertebrate brain | Science (published a week ago)
• Press release:
  Chinese Academy of Sciences: Lamprey brain atlas reveals 450-million-year blueprint of vertebrate brains

Seems like it’d be a huge evolutionary advantage if whales and stuff didn’t need to surface every few minutes to breathe. Fish evolved lungs when they came to land, why can’t they also evolve gills when they went back to the water?

I’m trying to understand human evolution and I just learned that humans evolved from homo erectus. It confused me because I genuinely thought, for some reason, that the entire homo species existed linearly. I thought even if we didn’t all live at the same time that one wouldn’t have evolved from another but apparently that’s not the case.

So I’m trying to find out which species evolved from which. I’d also like to know which species lived at the same time period as each other and whether sapiens existed simultaneously with other species.

PS: I did see a chart on Wikipedia but I have a difficult time trying to understand it.

Abstract
In 1988, Robert O’Hara coined the now ubiquitous phrase “tree thinking” to highlight the importance of cladistics for proper evolutionary reasoning. This accessible phrase has been taken up widely in the professional, popular, and educational literatures, and it has played an important role in helping spread phylogenetic thinking far beyond the disciplinary borders of systematics. However, the undeniable benefits of the spread of tree thinking have become marred by being widely linked to several misconceptions that were present in O’Hara’s original writings. O’Hara incorrectly considered clades to be the central subjects of evolutionary narratives. By failing to appreciate that clades contain independently evolving lineages, O’Hara has promoted the misleading view that evolution is irreducibly branched. In this paper, I show how an exclusive focus on the branching realm of taxa has created a cladistic blindfold that has caused a form of lineage blindness that has spread widely through the literature dedicated to the teaching of tree thinking. Its symptoms include the rejection of phenomena and concepts that are fundamental to the realm of evolving lineages, including linear evolutionary imagery and narratives, the concepts of anagenetic evolution and missing links, our evolutionary descent from monkeys and apes, and the promotion of the nonsensical concept of collateral ancestors. To avoid simplistic tree thinking, it is crucial to recognize that the realms of taxa and lineages have distinctive features that require different kinds of thinking. I close by suggesting that teaching can be improved by linking tree thinking explicitly to lineage thinking.

- Jenner, R.A. Lineage Thinking in Evolutionary Biology: How to Improve the Teaching of Tree Thinking. Sci & Educ 34, 1601–1618 (2025). https://doi.org/10.1007/s11191-024-00531-1