biogeography

There is a new paper out suggesting that the Flores hominids, known as Hobbits, were "human endemic cretins." From the abstract of this paper: ... We hypothesize that these individuals are myxoedematous endemic (ME) cretins, part of an inland population of (mostly unaffected) Homo sapiens. ME cretins are born without a functioning thyroid; their congenital hypothyroidism leads to severe dwarfism and reduced brain size, but less severe mental retardation and motor disability than neurological endemic cretins. We show that the fossils display many signs of congenital hypothyroidism, including…
In 1833, Darwin spent a fair amount of time on the East Coast of South America, including in the Pampas, where he had access to abundant fossil material. Here I'd like to examine his writings about some of the megafauna, including Toxodon, Mastodon, and horses, and his further considerations of biogeography and evolution. In the vicinity of Rio Tercero... Hearing ... of the remains of one of the old giants, which a man told me he had seen on the banks of the Parana, I procured a canoe, and proceeded to the place. Two groups of immense bones projected in bold relief from the perpendicular…
Everyone knows about Darwin's Finches, of the Galapagos Islands. But of course, Darwin made observations of birds throughout his travels on The Beagle. Here, I present a number of passages from The Voyage that include some of these observations. Struthio Rhea I will now give an account of ... the Struthio Rhea, or South American ostrich. This bird is well known to abound over the plains of Northern Patagonia, and the united provinces of La Plata. It has not crossed the Cordillera; but I have seen it within the first range of mountains on the Uspallata plain.... The ordinary habits of the…
Fallback foods are the foods that an organism eats when it can't find the good stuff. It has been suggested that adaptive changes in fallback food strategies can leave a more distinct mark on the morphology of an organism, including in the fossil record, than changes in preferred food strategies. This assertion is based on work done by the Grants and others with Galapagos Island finches, by Richard Wrangham and me with hominids, and by Betsy Burr and me with rodents. The reason for this is simple. There is a rough correspondence between how much energy one can obtain from a food type and…
Charles Darwin wrote a book called Geological Observations on South America. Since Fitzroy needed to carry out intensive and extensive coastal mapping in South America, and Darwin was, at heart, a geologist more than anything else (at least during the Beagle's voyage), this meant that Darwin would become the world's expert on South American geology. Much of The Voyage is about his expeditions and observations. Part of this, of course, was figuring out the paleontology of the region. Bahia Blanca is a port at the northern end of Patagonia. Chapter V of The Voyage begins: THE Beagle…
When reading The Voyage it is impossible to miss the observation that much of the time Darwin was engaged in adolescent boy behavior: Pulling the heads off insects, noting how long they would wiggle after cut in half, closely examining the ooze and guts, occupied much of his time. Obviously, careful observation and a strong stomach were not all that was required to think up Natural Selection and his other theories, or the Origin of Species would have been written dozens of times by dozens of grown up kids. In the following passages, Darwin is still along the Atlantic Coast, in "The…
Proposals to give the latter part of the present geological period (the Holocene) a new name ... the Anthropocene ... are misguided, scientifically invalid, and obnoxious. However, there is a use for a term that is closely related to "Anthropocene" and I propose that we adopt that term instead. The pithy title of the paper making this proposal is "Are we now living in the Anthropocene" (sic: no question mark is included in this title, enigmatically). It is not an entirely stupid idea. The paper argues that there are major changes of the type often used to distinguish between major…
The loss of sight in cave dwelling species is widely known. We presume that since sight in utter darkness has no fitness value, the mutation of a gene critical to the development of the sense of sight is not selected against. Over time, any population living in darkness will eventually experience experience such mutations, and these mutations can reach fixation. Astyanax mexicanus: Top is the surface, sighted form, bottom is the cave-dwelling, blind form. From the Jeffery Lab.Beyond this, we may hypothesize that a mutation "turning off" sight could be beneficial. By definition, an…
 Did humans wipe out the Pleistocene megafauna? This is a question that can be asked separately for each area of the world colonized by Homo sapiens. It is also a question that engenders sometimes heated debate. A new paper coming out in the Journal of Human Evolution concludes that many Pleistocene megafauna managed to go extinct by themselves, but that humans were not entirely uninvolved. The paper by Pushkina and Raia ("Human influence on distribution and extinctions of the late Pleistocene Eurasian megafauna") examines sources in the literature and a number of databases for Eurasian…
The end-Permian mass extinction event was the big daddy of all the known mass extinction events. Life on the planet Earth was almost entirely wiped out. A new paper explores the post-extinction recovery of ecological systems. Post extinction dynamics can be understood in relation to several dimensions: Taxonomy (the range and structure of different taxonomic groups); ecology (the interrelationship between the new species and the niches available, as well as the structure and distribution of those niches); and morphology (the overall morphospace filled by the new taxa). The present study…
There is a discussion on the internet about Junk DNA, that includes a discussion at Sandwalk (Larry Moran's blog) ... I made a comment there about genome size that was responded to by T.R. Gregory. I started to write my response in Larry's Little Box, but realized that it would not fit. So it is here: Imagine a gene family distributed among all the species in a given taxon. There are several alleles per gene. The gene codes for an enzyme that plays a role in determining cell size. Different combinations of genes/alleles exist to cause cell size to vary such that each species has a…
New research published in Science on the origins of multicellular life reveals an interesting pattern. The Cambrian Explosion may have been samosamo. What is evolution about? Why are there different species, rather than just one (or a few) highly variable species? Is there a close correspondence between the ecological "spaces" that organisms can fit and the adaptations ... represented by morphology, for instance ... of the species that do exist? Can you imagine a different world where instead of having 10,000 species of birds there is only one bird that is highly adaptable in its…
Plant and animal fossils recently discovered from an island in the Bahamas tell a story of habitat change and human involvement in local extinction. These finds are reported in a paper by Steadman et al. in the Proceedings of the National Academy of Sciences. Most people with an interest in natural history know about one or more regions that were at one time covered by "a great inland sea." For instance, if you live in the American Midwest, you probably know that much of this region was covered by such a sea, evidenced by extensive limestone beds and other geological manifestations. As…
Homo floresiensis more widely known as the "Hobbit," may have had arms that were very different from those of modern humans. A paper in the current issue of the Journal of Human Evolution explores the anatomy of H. floresiensis. To explore this we first have to understand the concept of "Humeral torsion." Humeral torsion is the orientation of the humeral head relative to the mediolateral axis of the distal articular surface. Don't bother reading that sentence again, I'll explain it. The humerus is the upper arm bone, that runs between your shoulder and your elbow. The humeral head is…
OK, so you are vacuuming the house, and along the way, you suck up a couple of spiders, some spier eggs, a beetle or two, and as the cat or dog walks by, you figure you're probably sucking up some fleas and flea eggs, and so on and so forth. SO you know all these cooties are now in the vacuum cleaner bag. When you are done vacuuming, you put the vacuum cleaner away. The thought is in your brain... all these creepy crawlers are now going to slowly work their way out of the vacuum cleaner and go back to their crawly creepy business. But you stop yourself from thinking further about it and…
The Central African Rainforest (as distinct from the West African Rain Forest) spans an area from the Atlantic coast to nearly Lake Victoria in Uganda and Tanzania. In fairly recent times (the mid Holocene) this forest was probably continuous all the way to Victoria, and probably extended farther north and south than one might imagine from looking at its current distribution. Within the forest are major rivers, including the Congo. The Congo River is the only major river in the world that crosses the Equator twice. This trans-equatorial configuration guarantees that the rivers picks up…
There seems to be some interesting things going on with the recently reported study of rates of evolution in humans. We are getting reports of a wide range of rather startling conclusions being touted by the researchers who wrote this paper. These conclusions typically come from press releases, and then are regurgitated by press outlets, then read and reported by bloggers, and so on. Here is, in toto, the press release from the University of Wisconsin, where John Hawks, one of the authors of the study, works. I reproduce the press release here without further comment. Genome study places…
All I have is the press release, but it's fun: Cosmopolitan microbes -- hitchhikers on Darwin's dust Scientists have analysed aerial dust samples collected by Charles Darwin and confirmed that microbes can travel across continents without the need for planes or trains - rather bacteria and fungi hitch-hike by attaching to dust particles. In a paper published in Environmental Microbiology, Dr. Anna Gorbushina (Carl-von-Ossietzky University, Oldenburg, Germany), Professor William Broughton (University of Geneva, Switzerland) and their colleagues analysed dust samples collected by Charles…
Or, to be less crude, did modern humans, having already evolved in Africa, interbreed with the local Europeans who were Neanderthals, and if so, did they produce fertile offspring ... and, did this happen in sufficient degree to have mattered at all to the genetics of later (but not necessarily living) people? In my opinion, the answer is, of course they interbred. There are many reasons to believe this if almost no way to prove it. Indeed, the evidence of this interbreeding is virtually nil. With every additional test of the interbreeding hypothesis using DNA, the null hypothesis of no…
Repost from gregladen.com One day, about six thousand years ago (or more like 15 thousand ... the timing of this is disputed) a volcano in the vicinity of Mwea, Uganda blasted a huge volume of stuff into the air, covering the surrounding landscape and choking off most of the life forms living in a nearby lake. (A very nearby lake ... the current configuration of the lake suggests that the volcano may have actually been beneath the lake at the time of the eruption). Over a very short period of time, we can presume that the land animals that would have been wiped out by this eruption…