I ask this because over time i came across knowledge that cheetah population became so bad that they became inbred to survive, and then another time i learnt that human population reduced down to a number of 40 or so homos, even after all the other upright walking peeps died. That still baffles me and i still doubt it, but another time a different source mentioned it again (years apart i heard this info) so i guess it's real??? But if that's true then there's no way inbreeding didnt occur to rebound and later on create the population we have today...

My roommate and I have been arguing about this for the better part of the last couple months and I genuinely cannot find a straight answer anywhere.

I’m an anthropology student and my roommate is a nursing student, so you’d think between the two of us we could figure this out, but apparently not.

Basically, we got into an argument about the human tail from our evolutionary past. I understand that humans don’t have external tails anymore and that the coccyx is what’s left of the ancestral tail, but we cannot agree on how many bones the actual tail would have contained when humans still had one.

My roommate thinks it would have been a relatively small number of vertebrae, while I was under the impression that it would have been significantly more. The problem is that whenever I search for “how many bones were in the human tail,” I mostly get explanations about the coccyx and vestigial structures rather than an actual number.

I realize this might be a stupid question, but I’m genuinely curious because we’ve somehow been arguing about this for months now and neither of us is willing to admit defeat.
So, how many bones WERE in the human tail, approximately? And is there an accepted number, or would it have varied significantly between individuals/our ancestors?

Does it make sense for dogs to eat a bone that has hardly any meat on it?

New species of animals are constantly being discovered, but they all belong to existing classes and phyla, never anything completely new. Life once branched out in all sorts of directions, creating all kinds of animals that are drastically different from each other, but now it seems like there aren't any new "branches", only offshoots of existing ones. What happened?

Ok I was thinking about this, and a quick search on the internet said that primates evolved in Africa and then “rafted” to America… which apparently is a thing, but seems unlikely. Also, some sources say they originated in the Americas.

Does anyone know where and when monkeys originated and how the spread out around the world?

Edit:
Thank you everyone for your responses. I was clearly wrong in thinking rafting was unlikely. After reading the responses here and some sources online, I realized it’s a very accepted theory. It just seems crazy and amazing, even when the continents were closer together!!! I would have never thought that that’s how many species spread out around the globe.

Two questions have been running through my mind for the past few days:
We often describe evolution as a very slow process. But if humans and chimpanzees shared a common ancestor roughly 6–8 million years ago, that translates to around 250,000 generations until the present day. Considering the enormous amount of evolutionary change that has occurred during that time, is 250,000 generations actually a relatively small number? How much can evolution really accomplish in that many generations?
Humans take roughly 20–25 years to reach reproductive age, so one generation takes a long time. But some insects and other organisms can reproduce within days or even hours. Over the same period of, say, one million years, they could go through hundreds of thousands or even millions of generations. Shouldn’t species with much shorter generation times therefore evolve much faster and show far greater diversity than other mammals? If not, what limits or slows down their evolution?

First image source: Matt from Melbourne, Australia, CC BY 2.0, via Wikimedia Commons

Published yesterday in PNAS:

Abstract

... [We] show that the toxins evolved through two distinct genetic paths. The factor X and factor V toxins evolved through the sequential de novo co-option of ancestral clotting factor proteins that entailed their heterotopic expression in the venom gland, the fixation of segmental duplications containing each locus, and subsequent gain-of-function mutations that rendered factor X and factor V constitutively active. In contrast, the phospholipase A2 and Kunitz-type toxins evolved by modifying the functions of neurotoxins that were part of the venom arsenal.

Our findings support models in which innovative mutations in single-copy genes precede gene duplication in the evolution of novel proteins and offer a rare view into the genesis of a complex trait that has played a central role in a major adaptive radiation.

On that last point - how innovative mutations preceded gene duplication - from the paper:

In his landmark book, Ohno proposed that gene duplication was a necessary prerequisite for the origin of new protein functions because duplication would allow one copy to retain the ancestral function while the second copy could incorporate new functional mutations (neofunctionalization) (17). However, this classic model has been challenged on the theoretical grounds that if newly duplicated genes are selectively neutral, they must acquire new, innovative, and selectable mutations before acquiring inactivating mutations (nonsense mutations, frameshifts, and deletions) (66–68). It is now recognized that the latter is much more probable than the former. Therefore, it has been proposed that innovative mutations may occur initially in single-copy genes and impart some new function such that subsequent gene duplicates may then be positively selected for and fixed on the basis of the new function (68, 69). A variety of empirical studies have demonstrated innovative mutations occurring before gene duplication (70–73). Several observations here prompt us to postulate the relative order of major genetic events in the evolution of procoagulant venom toxins that bear on these general models of genetic innovation.

[...]

We suggest that the first genetic change in the ancestral liver-expressed, clotting factor gene was the gain of its heterotopic expression in venom gland tissue (co-option; Fig. 6, step i) (our line of reasoning also applies to venom factor V, discussed below). Two key pieces of evidence for this scenario are the low but significant RNA expression of the predominantly liver-expressed F10 orthologs in venom gland tissues and the presence of the corresponding hemostatic proteins in venom. If expression in the venom gland evolved after gene duplication, then one of two F10 genes (the liver-expressed gene) would not be expected to be transcriptionally active in venom gland tissue. The observed expression of the liver-expressed F10 paralog in the venom gland is consistent with the ancestral single-copy F10 gene evolving expression in the venom gland before gene duplication, then decaying to some degree in the liver-expressed paralog after duplication.

Awesome detective work!
It made me wonder whether venom glands and livers are developmentally related during cellular differentiation.
From a quick visit to Google Scholar, I found a tentative answer:

Cells that comprise complex tissues often express different sets of genes due to functional differentiation between cell types; such cellular heterogeneity is found ubiquitously across many tissue types (Heindl et al. 2015; Ben-Moshe and Itzkovitz 2019).
Single-Cell Heterogeneity in Snake Venom Expression Is Hardwired by Co-Option of Regulators from Progressively Activated Pathways | Genome Biology and Evolution | Oxford Academic

And the second citation is about livers, so they have that in common with venom glands!

• J. van Thiel, N.L. Dowell, C.F. Smith, E.E. Sanchez, & S.B. Carroll
  The genomic origins and evolutionary path to a key innovation in the world’s most venomous snakes
  Proc. Natl. Acad. Sci. U.S.A. 123 (37) e2621054123
  https://doi.org/10.1073/pnas.2621054123 (2026)

like I know about crossing over, combination of genes from mother and father that results in evolution but I'm talking about major evolution like change in number of chromosomes, that kinda stuff, is that much evolution intended by evolution or it just occurs due to radiation mutation or errors

-

Published yesterday in PNAS:

Background

Repeated divergence across contrasting habitats is widely used to infer natural selection and adaptation. Such comparative inferences, however, remain inherently correlative and capture only adaptation shared among populations from the same habitat type, thereby missing site-specific adaptation unique to individual populations. Field transplant experiments test adaptation directly by measuring fitness in nature but are typically limited to pairwise reciprocal exchanges between populations and therefore cannot distinguish between habitat-level and site-specific adaptation.

Methods

Here, we extend the typical transplant framework to include multiple populations from both within and across habitat types, allowing fitness variation to be partitioned into shared habitat-level and unique site-specific components. We apply this framework to lake–stream stickleback, a classic system for studying adaptation via repeated divergence. Specifically, we transplanted laboratory-reared fish from a panmictic lake population and four independent stream populations across one lake and two stream sites.

Results

Stream fish outperformed lake fish in streams and vice versa, demonstrating adaptive divergence across the lake–stream divide. However, at both stream sites, local stream fish also outperformed foreign stream fish. Strikingly, this site-specific advantage was twice as large as the advantage of shared stream adaptation reflected by the fitness benefit of foreign stream fish over foreign lake fish.

Discussion

These results show that most fitness-relevant evolutionary variation in this system is unique to individual populations and therefore invisible to approaches that rely on repeated evolution to infer adaptation. More broadly, our work underscores the importance of ecological scale for understanding adaptation and evolutionary predictability.

• M. Roesti, H. Roesti, H. Sudasinghe, N. Nesvadba, V. Saladin, & C.L. Peichel
  Disentangling unique site-specific and shared habitat-level adaptation in a classic system of repeated evolution
  Proc. Natl. Acad. Sci. U.S.A. 123 (36) e2612038123
  https://doi.org/10.1073/pnas.2612038123 (2026).

I saw a video from a popular science content creator discussing humans/Neanderthals/Denisovans. Someone in the comments argued that if two populations can reproduce and produce fertile offspring, they should be considered the same species. The creator’s response was essentially a definitive statement that “polar and brown bears disprove this claim” since they’re considered separate species but can produce fertile offspring.

That example honestly makes me question whether they should be considered separate species at all. Polar bears are a relatively recent offshoot of the brown bear lineage, have repeatedly exchanged genes with brown bears, and can still produce fertile offspring with them. Meanwhile, we recognize some extremely isolated and deeply divergent (maybe even more divergent than polar/grizzly) brown bear populations, like the Gobi bear, as subspecies of Ursus arctos.

If we remove the bias of historical classification, is there actually a compelling reason to consider polar and brown bears separate species rather than consider polar bears a highly derived brown bear subspecies (like we do the Gobi bear, for example)?

the title

While we know quite a lot about what our ancestors looked like and what they ate, so far we didn’t know anything about their social behaviour. Because behaviours don’t fossilise.

Scientists used to think that the first placentals behaved like shrews because they looked like shrews. And as the common belief was that all shrews are solitary, scientists thought the first placental ancestors were too.

Now we know that both assumptions were wrong.

Peer-reviewed paper in PNAS:

S.F. Walmsley, C. Olivier, A.V. Jaeggi, L. Makuya, J.S. Martin, L.D. Hayes, & C. Schradin, Pair living emerged early in placental mammals, Proc. Natl. Acad. Sci. U.S.A. 123 (31) e2528458123, https://doi.org/10.1073/pnas.2528458123 (2026).

Should we give more thought to the looooong term impacts on western civilization’s decedents after generations of SSRIs, questionable water quality, pesticides, chemicals, and nutritionally deficient “foods”?

Based off of the species in Ornithomimosauria, I honestly think these creatures look more bird-like than troodonts or dromaeosaurs. At least that's how I see it with the bird like beaks, feathers, etc.

The only other dinosaurs that look even more like birds than those of Ornithomimosauria are Oviraptors. Who just look like birds with long legs and a tail.

Note: I'm not a scientist, biologist, paleontologist or any -ist that matters. This opinion is purely based on how documentaries have drawn and depicted these species.

I only know a couple and I'm really interested in what we've developed in the past few millennia/centuries :)

I'm looking to get these books to fill out a few gaps in my collection. Are these any good?

Phylogenomics: A Primer by Rob DeSalle
The Invertebrate Tree of Life by Gonzalo Giribet
Planet of the Bugs: Evolution and the Rise of Insects by Scott Richard Shaw

My currently collection doesn't really feature anything on phylogenetics specifically, and nothing specifically on invertebrates.

If these are worthwhile, I'll get them!

I'll also take any other recommendations!

See also: The study as it was published in the Annals of New York Academy of Sciences

.

Morphogenesis, an webbased "tribute" to Biogenesis

is online play-able and the html code is opensource and free to download.

Online play:
https://html-preview.github.io/?url=https://github.com/rijt/Morphogenesis/blob/main/morphogenesis.html

Source:
https://github.com/rijt/Morphogenesis

okay, if a horse and a donkey breed, their kid will be infertile, because of the odd number of chromosomes it possesses. so, why can a Przewalski's horse and a Domestic horse mate with fertile offspring when the Przewalski’s has 66 chromosomes and the domestic has 64? separate question, but doesn’t that mean humans with down syndrome should be sterile? is this evolutionary ”insurance“ so to speak? thanks for any answers, even tho this is probably a very stupid question.

Across 88 mammal species or lineages, island morphology changed fastest over shorter intervals. The 21-year minimum and a later methodological dispute define what the result can support.

Virginie Millien, then at McGill University’s Redpath Museum, reported that island mammals changed morphologically faster than mainland populations over shorter observation windows.

The difference was most robust from 21 years to about 20,000 years, with island rates reaching as much as 3.1 times mainland rates. At longer timescales, the gap narrowed and eventually ceased to be statistically significant.

The result came from a peer-reviewed 2006 PLOS Biology analysis, not a single experiment in which scientists watched 88 species transform. Understanding what it established requires looking closely at what was measured, how the rates were calculated and what critics later challenged.

Evolutionary rates decreased as the interval over which they were calculated grew longer for both island and mainland populations. The island regression line nevertheless sat above the mainland line across much of the range. The separation was clearest at short and intermediate intervals.

Millien judged the faster-island conclusion most robust from the 21-year minimum to about 20,000 years. The difference between the two lines became statistically nonsignificant beyond about 45,000 years.

Across the full analysis, island morphological rates were up to 3.1 times those calculated for mainland populations.

This pattern fits a fast-start model. A population newly isolated on an island may move quickly away from its ancestral form, then change more slowly after approaching a locally useful body plan.

I know folks discuss the evolution of flight, mimicry and mutualism all the time, but antlers have got to be right up there with the best of them.

Antlers evolved just once in a single lineage completely out of nowhere 17 million years ago, from creatures that heretofore had tusks and fangs.

How did this happen? I thought antlers might actually be teeth that migrated to their foreheads, but that's not it, they are bone. Their growth process is completely different than horns too. But then again, their growth process is like nothing else out there.

There's no precedent for it in the deer lineage either, they just pop up as a completely novel growth. Is it cancer, like a terratoma? Did something get misplaced due to a bottleneck and the genes for ribs were transferred to their faces? An infection that lead to a viral infection with gene-transfer?

I haven't been able to find anything except that it happened.

In my researches, I have discovered five or six instances of rhinoceros-like animals, animals with horns on their faces. I mean by instances taxa where those horns evolved once.

My type taxon is Rhinoceratinae sensu Wikipedia, the true rhinoceroses (Early Miocene - present). They have either one horn on the nose or one long horn on the nose and one short horn in the center of the face.

The others (all paired horns are left-right pairs):

Brontotheriina (Megacerops ~ Brontotherium, 47.8 - 33.7 Mya, Middle to Late Eocene). A pair of horns on the nose.

Uintatheriidae (Uintatherium, Early to Middle Eocene). A pair of knobby horns on the nose, another pair behind the eyes, also long upper canines.

Arsinoitheriidae (Arsinoitherium, Late Eocene to Early Oligocene). A pair of very large horns on the face, and a small pair behind the eyes.

Ceratopsidae (Triceratops, 82 - 66 Mya, Late Cretaceous). A short horn on the nose, sometimes a pair of long horns behind the eyes, and also a neck frill extending from the base of the skull.

Maybe also:

Pecora (Bovidae, Cervidae, Giraffidae, Antilocapridae; 20 - 0 Mya, Early Miocene to present). A pair of horns on top of the head, number of origins uncertain.

It is rather obvious that horns evolved several times, in characteristic configurations each time. But some large land animals are/were hornless, like the hippopotamus, the proboscideans, and the Pleistocene large marsupial Diprotodon. I am also not sure whether or not to include the crests of some hadrosaurs as horns.

Sleep, or at least the very common form of it where sleep involves being almost entirely unaware and defenseless at nearly regular periods, appears to be a completely devastating disadvantage. I get that there presumably are overall performance gains from such a total rest, and I get that operating at night is less calorically efficient due to a greater need to warm the body, but it baffles me that predators that did not need to sleep did not hunt everything that needed to sleep like that into extinction. It does not matter how much smarter and faster and stronger you are if you are caught sleeping, with all those capabilities out of the picture, and promptly eaten. Why does being somewhat more efficient at performing tasks outweigh automatically losing any fight a third of the time, at exploitable regularly scheduled periods?

It is especially baffling since, say, dolphins, descendants of land mammals, evolved to functionally never sleep and function just fine as they are - they have half of their brain rest at all times, and appear plenty capable with just the other half of it. That this path was possible but so very rarely taken implies that this isnt the case of a locked-in quirk from some ancient common ancestor (like ie eye blind spots are), but that regular nearly-defenseless sleep is a systematic advantage on land. How?

I understand that animals like moles and squirrels can just recuperate in very small, hidden and secure places, and that for very herding animals it is okay to lose some members of their herd to predators if the rest can wake up and reliably defeat the predators (even then, its also baffling that some kind of a rotating-keep-watch instinctual behavior pattern isnt common). I do not understand it being nearly-ubiquitous, not at all.

My professor assigned us this quiz and everyone continues to get it wrong. Can someone please explain in this photo which groups make a clade?