Sunday, July 15, 2018

Sabine Hossenfelder,
Research Fellow at the 
Frankfurt Institute for Advanced Studies

[[From my look at her writing she is a scientist who is exceptionally well informed in philosophy. ]]

Naturalness is an old idea; it dates back at least to the 16th century and captures the intuition that a useful explanation shouldn’t rely on improbable coincidences. Typical examples for such coincidences, often referred to as “conspiracies,” are two seemingly independent parameters that almost cancel each other, or an extremely small yet nonzero number. Physicists believe that theories which do not have such coincidences, and are natural in this particular sense, are more promising than theories that are unnatural.

Naturalness has its roots in human experience. If you go for a walk and encounter a delicately balanced stack of stones, you conclude someone constructed it. This conclusion is based on your knowledge that stones distributed throughout landscapes by erosion, weathering, deposition, and other geological processes aren’t likely to end up on neat piles. You know this quite reliably because you have seen a lot of stones, meaning you have statistics from which you can extract a likelihood.

As the example hopefully illustrates, naturalness is a good criterion in certain circumstances, namely when you have statistics, or at least means to derive statistics. A solar system with ten planets in almost the same orbit is unlikely. A solar system with ten planets in almost the same plane isn’t. We know this both because we’ve observed a lot of solar systems, and also because we can derive their likely distribution using the laws of nature discovered so far, and initial conditions that we can extract from yet other observations. So that’s a case where you can use arguments from naturalness.

But this isn’t how arguments from naturalness are used in theory-development today. In high energy physics and some parts of cosmology, physicists use naturalness to select a theory for which they do not have – indeed cannot ever have – statistical distributions. The trouble is that they ask which values of parameters in a theory are natural. But since we can observe only one set of parameters – the one that describes our universe – we have no way of collecting data for the likelihood of getting a specific set of parameters.

Physicists use criteria from naturalness anyway. In such arguments, the probability distribution is unspecified, but often implicitly assumed to be almost uniform over an interval of size one. There is, however, no way to justify this distribution; it is hence an unscientific assumption. This problem was made clear already in a 1994 paper by Anderson and Castano.

The standard model of particle physics, or the mass of the Higgs-boson more specifically, is unnatural in the above described way, and this is currently considered ugly. This is why theorists invented new theories to extend the Standard Model so that naturalness would be reestablished. The most popular way to do this is by making the Standard Model supersymmetric, thereby adding a bunch of new particles.

The Large Hadron Collider (LHC), as several previous experiments, has not found any evidence for supersymmetric particles. This means that according to the currently used criterion of naturalness, the theories of particle physics are, in fact, unnatural. That’s also why we presently do not have reason to think that a larger particle collider would produce so-far unknown particles.

In my book “Lost in Math: How Beauty Leads Physics Astray,” I use naturalness as an example for unfounded beliefs that scientists adhere to. I chose naturalness because it’s timely, as with the LHC ruling it out, but I could have used other examples.

A lot of physicists, for example, believe that experiments have ruled out hidden variables explanations of quantum mechanics, which is just wrong (experiments have ruled out only certain types of local hidden variable models). Or they believe that observations of the Bullet Cluster have ruled out modified gravity, which is similarly wrong (the Bullet Clusters is a statistical outlier that is hard to explain both with dark matter and modified gravity). Yes, the devil’s in the details.

Remarkable about these cases isn’t that scientists make mistakes – everyone does – but that they insist on repeating wrong claims, in many cases publicly, even after you explained them why they’re wrong. These and other examples like this leave me deeply frustrated because they demonstrate that even in science it’s seemingly impossible to correct mistakes once they have been adopted by sufficiently many practitioners. It’s this widespread usage that makes it “safe” for individuals to repeat statements they know are wrong, or at least do not know to be correct.

I think this highlights a serious problem with the current organization of academic research. That this can happen worries me considerably because I have no reason to think it’s confined to my own discipline.

Naturalness is an interesting case to keep an eye on. That’s because the LHC now has delivered data that shows the idea was wrong – none of the predictions for supersymmetric particles, or extra dimensions, or tiny black holes, and so on, came true. One possible way for particle physicists to deal with the situation is to amend criteria of naturalness so that they are no longer in conflict with data. I sincerely hope this is not the way it’ll go. The more enlightened way would be to find out just what went wrong.

That you can’t speak about probabilities without a probability distribution isn’t a particularly deep insight, but I’ve had a hard time getting particle physicists to acknowledge this. I summed up my arguments in my January paper, but I’ve been writing and talking about this for 10+ years without much resonance.

I was therefore excited to see that James Wells has a new paper on the arXiv 
Naturalness, Extra-Empirical Theory Assessments, and the Implications of Skepticism
James D. Wells
arXiv:1806.07289 [physics.hist-ph]
In his paper, Wells lays out the problems with the lacking probability distribution with several simple examples. And in contrast to me, Wells isn’t a no-one; he’s a well-known US-American particle physicist and Professor at the University of Michigan.

So, now that a man has said it, I hope physicists will listen. 

Wednesday, July 11, 2018

Slime Molds Remember — but Do They Learn?
Evidence mounts that organisms without nervous systems can in some sense learn and solve problems, but researchers disagree about whether this is “primitive cognition.”

[[Absolutely fascinating, and shows how little we understand.]]

Despite its single-celled simplicity and lack of a nervous system, the slime mold Physarum polycephalum may be capable of an elementary form of learning, according to some suggestive experimental results.
Audrey Dussutour, CNRS

July 9, 2018
Slime molds are among the world’s strangest organisms. Long mistaken for fungi, they are now classed as a type of amoeba. As single-celled organisms, they have neither neurons nor brains. Yet for about a decade, scientists have debated whether slime molds have the capacity to learn about their environments and adjust their behavior accordingly.
For Audrey Dussutour, a biologist at France’s National Center for Scientific Research and a team leader at the Research Center on Animal Cognition at Université Paul Sabatier in Toulouse, that debate is over. Her group not only taught slime molds to ignore noxious substances that they would normally avoid, but demonstrated that the organisms could remember this behavior after a year of physiologically disruptive enforced sleep. But do these results prove that slime molds — and perhaps a wide range of other organisms that lack brains — can exhibit a form of primitive cognition?
Slime molds are relatively easy to study, as protozoa go. They are macroscopic organisms that can be easily manipulated and observed. There are more than 900 species of slime mold; some live as single-celled organisms most of the time, but come together in a swarm to forage and procreate when food is short. Others, so-called plasmodial slime molds, always live as one huge cell containing thousands of nuclei. Most importantly, slime molds can be taught new tricks; depending on the species, they may not like caffeine, salt or strong light, but they can learn that no-go areas marked with these are not as bad as they seem, a process known as habituation.
“By classical definitions of habituation, this primitive unicellular organism is learning, just as animals with brains do,” said Chris Reid, a behavioral biologist at Macquarie University in Australia. “As slime molds don’t have any neurons, the mechanisms of the learning process must be completely different; however, the outcome and functional significance are the same.” ­­­­­­­
For Dussutour, “that such organisms have the capacity to learn has considerable implications beyond recognizing learning in nonneural systems.” She believes that slime molds may help scientists to understand when and where in the tree of life the earliest manifestations of learning evolved.
Even more intriguingly, and perhaps controversially, research by Dussutour and others suggests that slime molds can transfer their acquired memories from cell to cell, said František Baluška, a plant cell biologist at the University of Bonn. “This is extremely exciting for our understanding of much larger organisms such as animals, humans and plants.”
A History of Habituation
Studies of the behavior of primitive organisms go all the way back to the late 1800s, when Charles Darwin and his son Francis proposed that in plants, the very tips of their roots (a small region called the root apex) could act as their brains. Herbert Spencer Jennings, an influential zoologist and early geneticist, made the same argument in his seminal 1906 book Behavior of the Lower Organisms.
However, the notion that single-celled organisms can learn something and retain their memory of it at the cellular level is new and controversial. Traditionally, scientists have directly linked the phenomenon of learning to the existence of a nervous system. A number of people, Dussutour said, thought that her research “was a terrible waste of time and that I would reach a dead end.”

Audrey Dussutour, a biologist who studies animal cognition and the plasticity of organisms at France’s National Center for Scientific Research, holds a dish of cultured slime mold. She believes that such organisms might clarify how learning first evolved.
She started studying the slimy blobs by putting herself “in the position of the slime mold,” she said — wondering what it would need to learn about its environment to survive and thrive. Slime molds crawl slowly, and they can easily find themselves stuck in environments that are too dry, salty or acidic. Dussutour wondered if slime molds could get used to uncomfortable conditions, and she came up with a way to test their habituation abilities.
Habituation is not just adaptation; it’s considered to be the simplest form of learning. It refers to how an organism responds when it encounters the same conditions repeatedly, and whether it can filter out a stimulus that it has realized is irrelevant. For humans, a classic example of habituation is that we stop noticing the sensation of our clothes against our skin moments after we put them on. We can similarly stop noticing many unpleasant smells or background sounds, especially if they are unchanging, when they are unimportant to our survival. For us and for other animals, this form of learning is made possible by the networks of neurons in our nervous systems that detect and process the stimuli and mediate our responses. But how could habituation happen in unicellular organisms without neurons?
Starting in 2015, Dussutour and her team obtained samples of slime molds from colleagues at Hakodate University in Japan and tested their ability to habituate. The researchers set up pieces of slime mold in the lab and placed dishes of oatmeal, one of the organism’s favorite foods, a short distance away. To reach the oatmeal, the slime molds had to grow across gelatin bridges laced with either caffeine or quinine, harmless but bitter chemicals that the organisms are known to avoid.
“In the first experiment, the slime molds took 10 hours to cross the bridge and they really tried not to touch it,” Dussutour said. After two days, the slime molds began to ignore the bitter substance, and after six days each group stopped responding to the deterrent.
The habituation that the slime molds had learned was specific to the substance: Slime molds that had habituated to caffeine were still reluctant to cross a bridge containing quinine, and vice versa. This showed that the organisms had learned to recognize a particular stimulus and to adjust their response to it, and not to push across bridges indiscriminately.

In experiments conducted by Dussutour’s team, disks of yellow slime mold (at bottom) can eat plates of oatmeal (at top) — but only if they cross gelatinous bridges (at center) laced with noxious but harmless compounds. Here, the middle slime mold sample has learned to disregard the chemicals, a process called habituation.
Finally, the scientists let the slime molds rest for two days in situations where they were exposed to neither quinine nor caffeine, and then tested them with the noxious bridges again. “We saw that they recover — as they show avoidance again,” Dussutour said. The slime molds had gone back to their original behavior.
Of course, organisms can adapt to environmental changes in ways that don’t necessarily imply learning. But Dussutour’s work suggests that the slime molds can sometimes pick up these behaviors through a form of communication, not just through experience. In a follow-up study, her team showed that “naïve,” non-habituated slime molds can directly acquire a learned behavior from habituated ones via cell fusion.
Unlike complex multicellular organisms, slime molds can be cut into many pieces; once they’re put back together, they fuse and make a single giant slime mold, with veinlike tubes filled with fast-flowing cytoplasm forming between pieces as they connect. Dussutour cut her slime molds into more than 4,000 pieces and trained half of them with salt — another substance that the organisms dislike, though not as strongly as quinine and caffeine. The team fused the assorted pieces in various combinations, mixing slime molds habituated to salt with non-habituated ones. They then tested the new entities.
“We showed that when there was one habituated slime mold in the entity that we were forming, the entity was showing habituation,” she said. “So one slime mold would transfer this habituated response to the other.” The researchers then separated the different molds again after three hours — the time it took for all the veins of cytoplasm to form properly — and both parts still showed habituation. The organism had learned.
Hints of Primitive Cognition
But Dussutour wanted to push further and see whether that habituating memory could be recalled in the long term. So she and her team put the blobs to sleep for a year by drying them up in a controlled manner. In March, they woke up the blobs — which found themselves surrounded by salt. The non-habituated slime molds died, perhaps from osmotic shock because they could not cope with how rapidly moisture leaked out of their cells. “We lost a lot of slime molds like that,” Dussutour said. “But habituated ones survived.” They also quickly started extending out across their salty surroundings to hunt for food.
What that means, according to Dussutour, who described this unpublished work at a scientific meeting in April at the University of Bremen in Germany, is that a slime mold can learn — and it can keep that knowledge during dormancy, despite the extensive physical and biochemical changes in the cells that accompany that transformation. Being able to remember where to find food is a useful skill for a slime mold to have in the wild, because its environment can be treacherous. “It’s very good it can habituate, otherwise it’d be stuck,” Dussutour said.
More fundamentally, she said, this result also means that there is such a thing as “primitive cognition,” a form of cognition that is not restricted to organisms with a brain.
Scientists have no idea what mechanism underpins this kind of cognition. Baluška thinks that a number of processes and molecules might be involved, and that they may vary among simple organisms. In the case of slime molds, their cytoskeleton may form smart, complex networks able to process sensory information. “They feed this information up to the nuclei,” he said.
It’s not just slime molds that may be able to learn. Researchers are investigating other nonneural organisms, such as plants, to discover whether they can display the most basic form of learning. For example, in 2014 Monica Gagliano and her colleagues at the University of Western Australia and the University of Firenze in Italy published a paper that caused a media frenzy, on experiments with Mimosa pudicaplants. Mimosa plants are famously sensitive to being touched or otherwise physically disturbed: They immediately curl up their delicate leaves as a defense mechanism. Gagliano built a mechanism that would abruptly drop the plants by about a foot without harming them. At first, the plants would retract and curl their leaves when they were dropped. But after a while, the plants stopped reacting — they seemingly “learned” that no defensive response was necessary.

Slime molds are highly efficient at exploring their environment and making use of the resources they find there. Researchers have harnessed this ability to solve mazes and other problems under controlled conditions.
Traditionally, simple organisms without brains or neurons were thought to be capable of simple stimulus-response behavior at most. Research into the behavior of protozoa such as the slime mold Physarum polycephalum (especially the work of Toshiyuki Nakagaki at Hokkaido University in Japan) suggests that these seemingly simple organisms are capable of complex decision-making and problem-solving within their environments. Nakagaki and his colleagues have shown, for example, that slime molds are capable of solving maze problems and laying out distribution networks as efficient as ones designed by humans (in one famous result, slime molds recreated the Tokyo rail system).
Chris Reid and his colleague Simon Garnier, who heads the Swarm Lab at the New Jersey Institute of Technology, are working on the mechanism behind how a slime mold transfers information between all of its parts to act as a kind of collective that mimics the capabilities of a brain full of neurons. Each tiny part of the slime mold contracts and expands over the course of about one minute, but the contraction rate is linked to the quality of the local environment. Attractive stimuli cause faster pulsations, while negative stimuli cause the pulsations to slow. Each pulsing part also influences the pulsing frequency of its neighbors, not unlike the way the firing rates of linked neurons influence one another. Using computer vision techniques and experiments that might be likened to a slime mold version of an MRI brain scan, the researchers are examining how the slime mold uses this mechanism to transfer information around its giant unicellular body and make complex decisions between conflicting stimuli.
Fighting to Keep Brains Special
But some mainstream biologists and neuroscientists are critical of the results. “Neuroscientists are objecting to the ‘devaluing’ of the specialness of the brain,” said Michael Levin, a biologist at Tufts University. “Brains are great, but we have to remember where they came from. Neurons evolved from nonneural cells, they did not magically appear.”
Some biologists also object “to the idea that cells can have goals, memories and so on, because it sounds like magic,” he added. But we have to remember, he said, that work on control theory, cybernetics, artificial intelligence and machine learning over the last century or so has shown that mechanistic systems can have goals and make decisions. “Computer science long ago learned that information processing is substrate-independent,” Levin said. “It’s not about what you’re made of, it’s about how you compute.”
It all depends on how one defines learning, according to John Smythies, the director of the Laboratory for Integrative Neuroscience at the University of California, San Diego. He is not persuaded that Dussutour’s experiment with slime molds staying habituated to salt after extended dormancy shows much. “‘Learning’ implies behavior and dying is not that!” he said.
To Fred Kaijzer, a cognitive scientist at the University of Groningen in the Netherlands, the question of whether these interesting behaviors show that slime molds can learn is similar to the debate over whether Pluto is a planet: The answer depends as much on how the concept of learning is cast as on the empirical evidence. Still, he said, “I do not see any clear-cut scientific reasons for denying the option that nonneural organisms can actually learn”.
Baluška said that many researchers also fiercely disagree about whether plants can have memories, learning and cognition. Plants are still considered to be “zombielike automata rather than full-blown living organisms,” he said.
But the common perception is slowly changing. “In plants, we started the plant neurobiology initiative in 2005, and although still not accepted by the mainstream, we already changed it so much that terms like plant signaling, communication and behavior are more or less accepted now,” he said.
The debate is arguably not a war about the science, but about words. “Most neuroscientists I have talked to about slime mold intelligence are quite happy to accept that the experiments are valid and show similar functional outcomes to the same experiments performed on animals with brains,” Reid said. What they seem to take issue with is the use of terms traditionally reserved for psychology and neuroscience and almost universally associated with brains, such as learning, memory and intelligence. “Slime mold researchers insist that functionally equivalent behavior observed in the slime mold should use the same descriptive terms as for brained animals, while classical neuroscientists insist that the very definition of learning and intelligence requires a neuron-
Baluška said that as a result, it’s not that easy to get grants for primitive-cognition studies. “The most important issue is that grant agencies and funding bodies will start to support such project proposals. Until now, the mainstream science, despite a few exceptions, is rather reluctant in this respect, which is a real pity.”
To gain mainstream recognition, researchers of primitive cognition will have to demonstrate habituation to a broad range of stimuli, and — most importantly — determine the exact mechanisms by which habituation is achieved and how it can be transferred between single cells, Reid said. “This mechanism must be quite different to that observed in brains, but the similarities in functional outcomes make the comparison extremely interesting.”

That ultra-Orthodox flight delay? It didn’t happen
True, the El Al flight took off 70 minutes late, but it wasn't for the reason everyone thinks
[[Just for the fun of it.]]

JUL 11, 2018, 1:20 AM
Writing the following question, I am filled with trepidation and frustration: Does every fact that is publicized need to be checked out personally?
For the past week, I have been unable to fathom how an ultra-Orthodox person dared delay an El Al flight for more than an hour. How did such a thing happen? Who dared to act with such audacity? Which cabin crew members allowed him to behave like that? Of course, I was certain that the facts were correct. After all, they were published everywhere, and people talked about the incident. So the facts simply had to be correct.
Well, no. I received the following email from Katriel Shem-Tov:
“Dear Sivan, I was on that flight from New York, the one that the media reported ‘took off an hour and a quarter late because of the Haredim.’ My wife and I celebrated our silver wedding anniversary and at 6 p.m., we were supposed to take off on our way home. However, before we even boarded, there was an announcement of a 45-minute delay and take-off would be at 6:45 p.m. The same information appeared on the screen in the departure lounge. Of course, the delay had nothing to do with any of the passengers.
“Boarding took a long time, ’till at least 7:10, I believe. My guess is that the whole business with the Haredim didn’t take more than five minutes. Of course, I am not justifying their behavior and one should not cause a delay of even one minute. I am Haredi myself, but I have never seen such behavior like theirs.
“Then I heard you in the media expressing your outrage and I heard many other people who were so angry about the entire incident. Since I was actually a passenger on the flight, I cannot understand how everyone got so caught up in the story. It all sounds so unbelievable, how come no one actually checked the facts? It causes harm to Israel’s good name in the international arena, so why are we all in such a tizzy? It took me a few days to decide whether to contact you, but I feel it is important that the truth come out. There are many other passengers who can corroborate the story, if necessary.”
I contacted El Al straight away, and they responded with the following, surprising, statement:
“The details that were reported about the incident were not accurate, to put it mildly. In actual fact, the delay was totally unconnected to the incident. The plane’s journey to the runway at the airport in New York took about one hour and had nothing to do with the incident. Taking care of the two passengers who refused to sit in their allocated places occurred after the plane had already left the gate and only took a few moments. We will continue to do our best to transport our customers safely, comfortably, and according to schedule.”
I certainly do not intend this post to defend those two passengers. I do want to ensure that it will defend 8 million people from a heated public debate which has no basis in fact.
Sivan Rahav Meir is an Israeli television and print journalist, author and radio and TV host.

Thursday, July 5, 2018

Rafting Stormy Waters: When Biogeography Contradicts Common Ancestry
June 27, 2018, 1:08 AM

The orderly pattern of biogeographic distribution of plants and animals was one of the lines of evidence that Charles Darwin mentioned in support of his theory of common descent with modification. Likewise, modern presentations of evidence in favor of evolution almost never fail to mention biogeography. Indeed it is a neat fact that many organisms that are endemic on islands are most similar to species of the adjacent mainland, or that fossil kangaroos have been found exclusively in Australia, which happens to be their modern area of distribution. This orderly pattern of biogeographic distribution is usually explained by reference to either dispersal or vicariance (continental drift).
However, it is far from true that biogeography unambiguously supports common ancestry, or that patterns of biogeographic distribution always align well with the pattern of reconstructed phylogenetic branching or the supposed age of origin. Indeed, there are many tenacious problems of biogeography and paleobiogeography that do not square well with the evolutionary paradigm of common descent. Those problems include disjunct distributions of organisms that do not occur in adjacent regions (or at least regions that are thought to have separated by continental drift). Examples include freshwater crabs (Sternberg & Cumberlidge 2001); the colocolo opossum from Chiloe, more closely related to Australian marsupials than to other American opossums; the lichen genera Heteroplacidium and Ramboldia that are found in Australia, New Zealand, South Africa, and the Falkland Islands but also in the Mediterranean region, e.g., Sardinia (Australian National Botanic Gardens 2012); or the New World planthopper group Plesiodelphacinae in Japan (Asche et al. 2016). Sometimes it has been the discovery of fossils that created biogeographical puzzles, like the discovery of a fossil platypus from South America (Pascual et al. 1992), or a fossil hummingbird from Europe (Louchart et al. 2008), which destroyed the previously undisputed evolutionary stories about the endemic origins of these groups.
Ratite Birds
An iconic example of disjunct distribution is that of ratite birds. These include very large flightless birds like the African ostriches, the extinct elephant birds from Madagascar, the South American rheas, the Australian emus, the cassowaries from Australasia, and kiwis and the extinct moas from New Zealand. Most biologists assumed that ratites are monophyletic and originated from a common flightless ancestor, and that their disjunct distribution is explained by the breakup of the ancient southern supercontinent Gondwana. Unfortunately, a few problems spoil this delightful just-so story:
  1. Moas do not seem to be more closely related to the New Zealand kiwis (Cooper et al. 2001Haddrath & Baker 2001).
  2. Instead, the elephant birds of Madagascar are claimed to be the closest relatives of the New Zealand kiwis (Mitchell et al. 2014).
  3. The breakup of Gondwana is much too long ago to explain the distribution of ratite birds by continental drift (vicariance biogeography), which cannot have originated before the Paleogene according to fossil and molecular clock evidence (Prum et al. 2015).
But wait, there is help from cladistics: Just shake the tree and reshuffle the taxa, so that all the ostrich-like birds could have evolved independently by multiple convergence from flying ancestors, and their biogeographic distribution could thus be due to normal aerial dispersal. This was suggested by the genomic study of Harshman et al. (2008), who found the flying tinamous to be nested within flightless ratite birds. This is, of course, contradicted by many morphological characters that unite all ratites, as well as by molecular data, and Harshman even mentions five recent studies that strongly supported ratite monophyly. These conflicting data were ignored in Harshman’s DNA study that was crafted by not fewer than 19 co-authors. Certainly the new molecular tree must be so robust that the new molecular evidence outweighs the conflicting evidence. Except that that is not the case: indeed Harshman et al. (2008) presented two very different trees, one in which tinamous are closer to rheas, and one in which they are closer to cassowaries, emus, and kiwis. But who cares? At least we got rid of an inconvenient biogeographical problem. 
Unfortunately, there is more: In a study, Haddrath & Baker (2012) confirmed that tinamous nest within ratites, but now they are more closesy related to the extinct moas, while rheas are closer to kiwis, cassowaries, and emus. Certainly, now we’ve got it right, at least till the next study with other genes, like that of Smith et al. (2013), who again got two different results for the position of tinamous like Harshman et al. (2008). Meanwhile a new study by Baker et al. (2014) vindicated the result of Haddrath & Baker (2012) (note that Scherz 2013 disputed all the alleged evidence for a position of tinamous within ratites). Isn’t phylogenetic tree reconstruction a wonderful science?
Freshwater Snails on South Pacific Islands
Zielske et al. (2016) described the enigmatic pattern of long-distance dispersal of minute freshwater gastropods of the family Tateidae across the South Pacific, presumably during the Paleogene by birds as vectors. They found that the more remote archipelagos harboring the genus Fluviopupa were colonized from New Zealand with a complex westward dispersal, so that “geographical distance was not an appropriate predicator of phylogenetic relationship.” Aha! Let me translate this into plain English: the biogeographic pattern does not support common ancestry, but has to be explained away with ad hoc hypotheses.
The Rafting Hypothesis for Oceanic Dispersal
Anyway, some of the biggest biogeographic problems are posed by organisms that must be assumed by evolutionists to have dispersed across oceans via rafting to other continents (many examples are listed by Luskin, and de Queiroz 2005). This rafting hypothesis was first suggested by Alfred Russel Wallace, and elaborated by modern evolutionists, who have even proposed floating islands as a mode for long-distance dispersal of vertebrates across oceans (Houle 1998). Nevertheless, even the famed paleontologist George Gaylord Simpson (1940) acknowledged that “this sort of adventitious migration is dragged in when necessary to explain away any facts that contradict the main thesis.” Well said!
Trapdoor Spiders
Among the very diverse spider fauna of Australia there is one species that stands out: the tree trapdoor spider Moggridgea rainbowi, which only occurs on Kangaroo Island, but has its closest relatives of the same genus living in Africa. A phylogenomic study suggested that the Australian species separated from its African con-generic sister species about 2-16 million years ago, which is much later than the separation of the Australian and African continents around 95 million years ago. Therefore, it was recently proposed by Harrison et al. (2017) that large tarantulas rafted 6,000 miles across the wild Indian Ocean from Africa all the way to Australia (PLOS 2017), and not to the long coast of Western Australia but to a small island near Adelaide in South Australia. Professor Andrew Austin, the PhD supervisor of the publication’s lead author, Sophie Harrison, said in an interview, “At first thought, this does seem incredible” (University of Adelaide 2017). At first thought? I give it a second and third thought and still find it incredible.
Worm-lizards (Amphisbaenia) are a distinct (mostly legless) subgroup of squamate reptilians. They are bizarre and cryptic predators with a burrowing way of life, which raises the problem how to explain their disjunct distribution in South America, Africa, the Middle East, and parts of North America and Europe. A phylogenetic study suggested that the South American and African forms only separated about 40 million years ago, when both continents were already widely separated by the south Atlantic Ocean. Therefore, biologists are forced to assume that these subterranean animals rafted across the ocean. Actually, they have to assume not one but at least three (maybe even five) trans-oceanic dispersals (Longrich et al. 2015): from North America to Europe, from North America to Africa, and from Africa to South America. To address the fact that something like this is not only highly unlikely but indeed has never been observed, scientists invoke millions of years like a magic wand to allow for ridiculously improbable explanations within geological timescales (Panciroli 2016). 
Iguanas and Boine Snakes on Pacific Islands
Iguanas and boine snakes are mostly found in America, except for their enigmatic occurrence on Madagascar and on the two Pacific islands of Fiji and Tonga, far away from the American continent. Again scientists have preferred an explanation suggesting that these animals arrived on these islands by rafting on floating mats of vegetation, which would have taken about six months for the 5,000-mile journey (University of Chicago Press 2010). However, this leading explanation was recently disputed in favor of terrestrial dispersal via hypothetical land bridge connections (Noonan et al. 2010). Of course, this new hypothesis has its own problems and needs several ad hoc hypotheses, because we have no independent evidence for a land connection to Asia and/or Australia at the crucial time in Earth history, and fossil and subfossil iguanids are absent from Australia and other (in-between) Pacific islands. Noonan et al. frankly admit that they could “not conclusively demonstrate[e] the path to the Pacific for boine snakes and iguanid lizards,” but nevertheless these scientists preferred their new hypothesis over “the greatest vertebrate rafting event ever proposed.” Obviously they considered such an event as too unlikely to be true. But why is that, if millions of years are supposed to make even the most unlikely stuff easily possible, multiple times over? 
Concerning the occurrence of iguanas and boine snakes on Madagascar, a colonization via the Indian subcontinent has been proposed, because fossil representatives of these two animal groups are known from Asia but not from Africa (Vences 2004). The nagging problem is that the Malagasy iguanid genera have been found to be nested within South American species. This is another biogeographical enigma that does not fit well with the standard evolutionary narrative.
New World Monkeys
The most famous example of assumed rafting dispersal is the case of New World monkeys (Platyrrhini). The oldest fossil record of this primate group is Bransinella boliviana from a 26-million-year-old late Oligocene locality in Bolivia, and Perupithecus ucayaliensis from the Late Eocene (around 41 million years ago) of Peru, which agrees with an evolutionary age of New World monkeys dated by molecular clock at about 37-40 million years. The closest proposed relatives are Talahpithecus (Oligopithecidae) and Proteopithecus (Proteopithecidae) from the Eocene of North Africa, so that most primatologists think that New World monkeys evolved in Africa before crossing the Atlantic Ocean (Bond et al. 2015). Neither fossil nor living representatives are known from America north of Mexico, so that colonization via an Asian-North American land-bridge seems very unlikely, especially as South America was separated from North America from 80-3.5 million years ago. South America separated from Africa by continental drift about 90-120 million years ago, which is much too old for the ancestors of New World monkeys to have travelled with the drifting continent, as these ancestors only appear in the Eocene. Nobody has any plausible idea how the ancestors of New World monkeys could have managed to cross the whole Atlantic Ocean from Africa to South America, because single animals rafting on trees seem to be an absurd explanation (Fleagle & Gilbert 2006), for which there is not a single modern observation. This especially holds because you would need a viable population of at least a few conspecific male and female animals at the same place and time. Estimates vary between 10-100 conspecific individuals that would have been required as a founder population for New World monkeys. That would have required a big raft for sure, and the Atlantic was at least 1,400 km wide in the Eocene. The problem of survive such a rafting journey across the ocean is complicated by the fact that even small mammals from arid regions (e.g., degus) cannot survive more than two weeks without fresh water, but the journey would have taken at least 60 days when relying on currents and still at least 14 days with “sailing” (Gabbatiss 2016). Sailing? No problem, you just need floating islands with vertical trees acting as sails. Wow, the imagination of evolutionists is nearly unlimited. One wonders if they have ever been on a boat on the ocean in stormy weather.
But as Donald Prothero has confirmed (Prothero 2015), “monkeys were not the only colonists to reach South America by rafting from Africa. It turns out that there are lots of animals that did the same thing: geckos, skinks, tortoises, the blind burrowing reptiles known as amphisbaenids, and even the peculiar birds known as hoatzins. Most impressive of all were the caviomorph rodents.” Yes, even rodents and birds are believed to have crossed the ocean on rafts (Poux et al. 2006Naish 2011). It looks like there was some very busy ocean travel going on in those times, which suddenly stopped as soon as humans could have observed and recorded it.
Yes, it is a fatal problem for the fantastic rafting hypotheses that in the entire history of human seafaring there exists not a single documented case where larger terrestrial animals were actually observed rafting in the middle of a large ocean. The only empirical observation for rafting dispersal is a group of 15 Anolis lizards found in 1995 washed ashore on a Caribbean island, having apparently drifted after a hurricane 200 miles from the island of Guadeloupe to Anguilla, which both belong to the Leeward Islands of the Lesser Antilles in the Caribbean (Censky et al. 1998). Another case seems to be an Aldabra giant tortoise washed ashore on the coast of East Africa, probably having been drifting the 740 km distance for about three weeks (Gerlach et al. 2006). Charles Darwin hoped to solve such problems with the claim that given enough time, many things that are unlikely can happen, and “thus, neo-Darwinian evolutionists are forced to appeal to ‘unlikely’ or ‘unexpected’ migration of organisms, in some cases requiring the crossing of oceans to account for the biogeographical data. This kind of data may not necessarily absolutely falsify Darwinism, but at the least it challenges the simplistic argument that biogeography supports universal common descent through congruence between migration pathways and evolutionary history. In many cases, the congruence is simply not there” (Luskin 2015). There is a further problem though: we meanwhile have substantial paleobiogeographical evidence that such dispersal by rafting simply did not happen in either direction even in cases of much smaller distances and long periods of time (Krause 2001Clyde et al. 2003), as for example during the Cretaceous between Africa and Madagascar (even though this is complicated by the issue of paleocurrents; Ali & Huber 2010), or between India and Asia when the Indian subcontinent was close but not yet attached to Asia.
In all these examples a polyphyletic view much better agrees with the empirical evidence than does universal common descent. The latter explanation creates almost unresolvable problems of impossible routes of dispersal or a much too early dating of vicariance events that conflicts with the actual fossil record or the geological data on continental drift. At least the existence of such conflicting evidence should be acknowledged by evolutionists, but of course this does not happen and instead we are confronted with an endless flood of ad hoc hypotheses that try to explain away the conflicting evidence and even claim it as support for evolution.