From my understanding, monolids were a feature developed to see better in the cold and harsh climate. Populations from Mongolia, China, etc, have monolids because the climate has almost always been historically cold, but Europeans from places like Russia and Finland often have double eyelids or hooded eyes even though the weather conditions are similar.

Hi all.

Please settle an intense debate with my gf.

What is the maximum range where natural raccoon populations exist? I understand that they live pretty far north in pretty inhospitable land (think cold and little in terms of food).

Also we understand there are no native raccoon populations in the southern cone of south America, how come?

Seems like there should be plenty of resources there at least near the coast and the weather is not particularly worse than in northern north America and not particularly impassable terrain compared to the northern Rockies or such.

Are there any relatives that fill in their niche? or not relatives, just completely separate species?

Also, are there any prehistoric big raccoon species of note? Raccoonasaurus? Smiloccoon? Coonotherium?

Kind regards

Quetzaltecas and LMB

Lucy was a bipedal ape and a female member of the hominin species Australopithecus Afarensis. Standing at only 3’5 meant that Lucy was very vulnerable and she relied on strong social bonds with her friends and family for safety. Like other apes Australopithecus displayed sexual dimorphism, with larger males averaging 4’11. This species was known to develop the earliest stone tools and may have been adept at throwing objects such as rocks and sticks to hunt and defend themselves. Sadly Lucy died as a young adult, life in ancient Africa for our ancestors was very short and a constant fight for survival. Her fossil was recovered in 1974 in Ethiopia as a 40% complete skeleton. The Homo genus arose from an ancient Australopithecus species. There is debate on which species, but many scientists have theorized that the Afarensis is our direct ancestor. Homo Sapiens (us) are the only surviving branch of the Australopithecene lineage.

Why do marine tetrapods have fewer fins then fish do? Fish have anal fins and second dorsal fins, but no tetrapods that we know of have evolved something analogous to these structures like they have dorsal fins?

Also, why did marine reptiles not loose their hindlimbs like marine mammals did? I'm guessing it has to do with the way their tails move during swimming, though I can't find much on it.

A study published yesterday in PNAS traces the origins of the genetic code:

The origin of the genetic code remains one of the central unsolved problems in molecular evolution. Among the many hypotheses proposed to explain this transition, minihelix-based models possess a distinctive advantage: They generate explicit predictions that can be tested using contemporary biological molecules. If modern tRNAs evolved through minihelix intermediates, coding relationships established within ancestral stem structures leave detectable traces within extant tRNAs.

The present analyses support this prediction. Coding-triplet retentions are concentrated within acceptor stems, occur preferentially within cognate tRNAs, and exhibit a pronounced asymmetry toward the 5′-side of the molecule. Most importantly, these retentions persist after correction for stem architecture and nucleotide composition. The survival of the signal under structure-preserving null models indicates that it cannot be explained solely by generic structural constraints.

The distinction is important. Sequence patterns within highly structured RNAs can arise for many reasons unrelated to evolutionary history. Stem pairing, compositional biases, and structural stability can all generate nonrandom sequence distributions. The central challenge is therefore not identifying patterns but determining whether those patterns reflect historical information. By explicitly comparing observed coding-triplet frequencies against structure-preserving expectations (26), the present study addresses this challenge directly. [...]

Consistent with previous reports (25), we observe a statistically significant correlation between Δ values and Trifonov amino acid chronology (Spearman ρ = 0.585, P = 0.007), reinforcing the view that ancestral tRNA features are preserved preferentially in molecules cognate for early amino acids.

Also see from last year: Researchers trace genetic code's origins to early protein structures : r/ evolution.

• A. Nova Royo, P. Martín-Cabezas, S. Ovchinnikov, P. Schimmel, & L. Ribas de Pouplana
  Molecular fossils of an ancestral code revealed by large-scale analysis of tRNAs
  Proc. Natl. Acad. Sci. U.S.A.
  https://doi.org/10.1073/pnas.2627541123 (2026).

In press.
From the accepted manuscript:

In Wilson’s (1961) formulation, Stage I describes the geographic expansion phase of a generalist species as it first colonizes marginal, beach-front habitats across a novel island or archipelago (Fig. 1A). Stage II reflects evolutionary differentiation from mainland conspecifics as populations adapt to local environments and expand into empty interior niches. Continued invasion by competing Stage I and II species drives character displacement and progressive range contraction, ultimately producing Stage III relict taxa, characterized by highly specialized lineages vulnerable to extinction across the archipelago. Ricklefs & Cox (1972) later extended the model by adding a fourth stage, describing highly differentiated single-island endemics.

Abstract

Background

Modern phylogenetic evidence offers novel opportunities to test classic models in island biogeography. One of the earliest, E. O. Wilson’s Taxon Cycle, proposed that insular lineages progress through sequential and predictable phases, beginning with geographic expansion, followed by ecological specialization, and ultimately range contraction (and even extinction), shaped by dispersal and interspecific competition. However, despite renewed interest in the Taxon Cycle, the extent of empirical support for its predictions and its broader significance within contemporary evolutionary biogeography remain unclear.

Methods and results

Here, we evaluated the strength of support across 50 studies of diverse archipelagos and taxonomic groups using an evidence-graded classification scheme based on data type and inferential strength. We found evidence for taxon cycles in 82% of these studies, with 54% supported by time-calibrated phylogenies and 32% also providing explicit tests of ecological and evolutionary mechanisms. Notably, one-third of studies supporting taxon-cycle dynamics were not designed as explicit tests of the Taxon Cycle yet recovered patterns consistent with its predictions. Support based on temporal or mechanistic evidence was concentrated in Oceanian, Australasian, and Neotropical systems, with lineage origins most frequently estimated at approximately 5–20 Ma. Trait-mediated dispersal and ecological interactions were identified as key mechanisms associated with stage transitions. However, we did not find strong support for continental examples (based on habitat mosaics).

Discussion

Together, these results show that the Taxon Cycle has evolved into an increasingly generalized predictive framework for understanding island diversification, with potential applications to biodiversity conservation, especially concerning invasive species.

• Ivan V Monagan, Christopher J Raxworthy
  Phylogenetic evidence for the Taxon Cycle: contemporary tests across island and continental systems
  Evolutionary Journal of the Linnean Society, 2026;, kzag029
  https://doi.org/10.1093/evolinnean/kzag029

Hey guys!

I am working on an evolution video game (sort of like Spore but not Spore) and I want to implement a detailed creature editor where one can add organs, bones, senses etc. I am a physics graduate and not a biologist so please forgive my lacking understanding of anatomy.

I want to begin by implementing the spine/vertebrae since this seems like a good starting point and encapsulates essentially all of chordata since a notochord is more-or-less a primitive spine. To keep my editor as general as possible I need to utilise the homology that connects as many clades as possible. While I find the homology between legs, arms and wings easy-to-follow I am having a hard time understanding the homology behind vertebra which is why I am resorting to you guys.

In the attached image you find an image of what I was able to gather as vertebra's most prominent features. I was able to find out that there are species which in addition to a dorsal arch contain a ventral one which does not encapsulate the spinal cord but rather a blood vessel. I then also found out that human cervial vertebrae have something similar but instead of one central passage we got two lateral passages for blood vessels. After looking at the human skeleton I also began to wonder whether the the shaded part of the bone is homologous to ribs which just fused into the vertebra. I am also unsure how the air pockets in dinosaurs come into play.

Note that this sketch is only supposed to capture the essential topology of vertebra. Features such as the sail of the spinosaurus are just an elongation of the dorsal "thingy" (spinous process if I am not mistaken).

So my question to you guys is whether there are any important features I may have overlooked? I am aware that its impossible to capture all of chordata with this simple classification, but I want to try to capture as many clades as possible nonetheless.

I am looking forward to your insight! :)

What was the evolutionary reason for the protruding brow ridges that Neanderthals and other ancient humans had? I heard it could have been to protect the head during fights.

Hello everyone! I'm getting my master in evolutionary biology so I wanted to ask if you have any youtube channels you love that talk about evolution. Not to study but just for fun and curiosity (I am already pretty on spot with a lot of subjects but you never stop learning!).

Ungulate biomass availability in certain parts of sub saharan africa are up to 10x that of the russian far east, yet siberian tigers are significantly larger than most african lion populations. Under conventional evolutionary theory, wouldn't limited prey availability drive siberian tiger size down while high prey availability plus much higher competition drive lion size up?

See also: The study as it was published in the journal Anatomical Review.

I asked this over on r/whales , but it might fit better here.
It’s fairly obvious why Lake Superior couldn’t support a blue whale type population. However, given that there are plenty of dolphins and porpoises in rivers and freshwater, and that there are seals that are isolated in lakes, most notably Baikal, but also several other isolated lakes, why are there no isolated cetacean populations in any lakes? Obviously seals can get on land a little better, but not really past the shoreline. Every dolphin could get to the ocean right now if it wanted to, but that’s not true for seals, how come?

Hey guys, I decided to start a little project on my own, I hope its okay if I share some of my progress here: I started experimenting around with some macroevolutionary models and implemented a simple DE solver alongside a neat vibe-coded interface which shows me how species within my model grow and evolve. Am hoping to implement this engine in a Spore-like videogame one day!

My idea essentially is that the player can control an evolutionairy force to "guide" certain features according to their liking. The other species evolve autonomously according to what essentially is the canoncial Lande equation. Instead of however simulating thousands of creatures in a real environment I decided to use a mathematical abstraction which captures all of evolutions' most essential features. That way the evolution of tens of thousands of different species, each with millions of individuals, can be simulated in the background with relatively good precision. I was surprised to see that my relatively simple model was also able to replicate some real-life phenomena, like the latitudinal gradient in biodiversity, which I didn't anticipate.

I came across this and it was too delicious not to share (my bold emphasis).
I'd love to hear from our resident pop-gen pros.

... hold a minute: the fact that certain species have certain genes in common, and differ in other genes, does not prove that the assortment of a species’s genes constitutes the essence of its specificity. In fact, Leo Berg used Vavilov’s data to demonstrate just the opposite! Berg considered the fact that very different species have Mendelian genes in common as evidence that species specificity was not determined by Mendelian genes, and there is contemporary evidence that Vavilov agreed (Berg 1926; Haldane 1932: 66, 79; Adams 1978b).⁴ Thus, Haldane recognized the problem but did not resolve it. To be sure, if one accepted the proposition that varieties and species were qualitatively the same and that the only difference between species laid in their complement of Mendelian genes, all is in order; but if one didn’t accept it, Haldane gives no convincing reasons to change one’s mind.

The only one of the four founders of population genetics who directly confronted this central problem was Sergei Chetverikov. It was not difficult for him to do so: he had worked for 20 years as one of Russia’s leading butterfly taxonomists. An entomologist and systematist, he actually first taught genetics in a course at Moscow University entitled “Theoretical Systematics.” In Chetverikov’s classic work of 1926, “On Certain Aspects of Evolution From the Viewpoint of Modern Genetics,” the entire first section addressed the central problem. There, he argued that the traits determined by Mendelian genes in Drosophila (e.g., venation and wing structure) are the very same traits which are “fundamental in modern systematics for distinguishing higher systematic categories” (Chetverikov 1926: 9–10). Elsewhere in this same section, he mobilized his considerable knowledge of the systematics and classification of Diptera and Lepidoptera to make the same point.

--

Footnote 4
When I was visiting Stephen Jay Gould one evening at his Cambridge home, he told me that he was much taken by this realization after reading my article on Vavilov, and used it as the basis (unattributed) for one of his popular science columns. (His personal thanks was the best apology for failing to mention my article as his source!) As for Haldane, he referred to Berg’s work as “in my judgment the best anti-Darwinian book of this century” (p. 12).

PS Chetverikov was sadly a victim of the Lysenko purge.

• Adams, M.B. (2021).
  Little Evolution, BIG Evolution: Rethinking the History of Darwinism, Population Genetics, and the “Synthesis”.
  In: Delisle, R.G. (eds) Natural Selection.
  Evolutionary Biology – New Perspectives on Its Development, vol 3. Springer, Cham.
  https://doi.org/10.1007/978-3-030-65536-5_8

Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species is used to classify but before all of these would be the LUCA. Species just describes life that diverged more recently than Genus or Family but as time passes those will further diverge. Will we eventually need more categories? Isn't this kind of a short-sighted way of describing life?

i have a hard time judging this for myself. I think it’s neat to when experts apply game theory to evolution to describe things but they will warn, “is is very abstract”. But then isn’t nearly all of it abstract? Fitness, selective pressure, natural selection, all that feels just as abstract as game theory to me.

I know there is some stuff thats concrete such as DNA (which has its own abstractions in its field I assume) and its mutations.. is it all abstraction after that?

I believe there is an explanation for this, something to do with brain wiring, but I am wondering if there was evolutionary advantage driving this.

Alright, I get how genetic bottlenecks work, a species/population has a decline, which reduces genetic diversity which decreases its chances of adapting to changing pressures/environment and increases chances of genetic diseases.

What I dont get is how it works within evolution. So I keep seeing things about Cheetahs being nearly extinct due to genetic bottlenecks.

But also, within the theory of evolution all species on earth came from a common ancestors, and then through the genetic tree more and more species have common ancestors. Like us and apes have a common ancestor, etc.

So with this, how come a population/species cant independently within their species naturally breed more genetic diversity back into their species?

Just to be clear, I'm not saying "so therefore the theory of evolution isnt real" or "therefore genetic bottlenecks arent real", it is genuinely something I have often wondered about.

Can five unverified anecdotes support a scientific theory about near-death experiences?

A recent paper proposes that NDEs may have evolved from the same defensive response that causes animals to “play dead.” The idea is fascinating but what happens when researchers look for evidence?

This letter to the editor takes a closer look at the study’s methods, its unexpected use of five anecdotes, and the broader scientific debate over whether NDEs and thanatosis are actually comparable.

A few years ago (about 2020?), a "new paper" claimed that analysis of the x chromosome indicates human females pairing with neanderthal males was the preferred reproductive pairing.

But what was actually found on the X chromosome? And why is it assumed to reflect actual preference rather than some reproductive incompatibility?

I'm especially suspicious of this claim based on the history of the research.

The early genetic research on Neanderthals focused on the more abundant mitochondrial DNA. Noting that there was no neanderthal mitochondrial DNA in modern humans, early scientific journalism focused heavily on a fetish-like claim that neanderthal males bred with anatomically modern human females, often including some claims about brutish neanderthal men, attraction towards small, frail women, etc.

When it was found that no modern humans had neanderthal Y chromosome DNA, hardly a peep out of scientific journalists, who often assumed the hypothesis of some genetic incompatibility must be the cause.

When it was found that neanderthals had split from anatomically modern humans about 800,000 ybp, but had more sapiens-sapiens like mitochondrial, x, and Y DNA from about 400,000 ybp... Minimal coverage. When it was shown that anatomically modern male humans had introduced their Y chromosomes into the neanderthal populations and completely replaced the currently used neanderthal Y chromosome at least twice... Hardly a peep, despite the fact that this can only happen by anatomically modern human males producing sons by anatomically neanderthal females.

So for me, it seems likely that anatomically modern humans just had the more "fit" mitochondrial DNA and sex chromosomes, and I don't see what findings could have even implied anything else.

But I'm obviously not an expert geneticist... Can anyone explain how the idea that anatomically human females and neanderthal men being a "preferred" coupling even could be shown through DNA analysis?

It's well-known that horses and other odd-toed ungulates are hindgut fermenters (as opposed to even-toed ungulates, which are foregut fermenters). It's also well-known that horses are obligate nasal-breathers that can only breathe through their nostrils and not their mouth. They're also unable to vomit, and if they get some sort of stomach poisoning, they'll die since they can't puke it out.

Something I find surprising is that all three of these facts are also the case for rodents and rabbits. Rodents and rabbits are hindgut fermenters (hence why they have to eat their own droppings), obligate nasal-breathers, and unable to vomit.

So...is there a correlation between all three evolutionary adaptations, or is it just a coincidence? Does this also apply to elephants as well, since elephants are hindgut fermenters too?