Origins of Darwin’s Evolution: Solving the Species Puzzle Through Time and Place by J. David Archibald does something that not enough studies of Darwin’s work do: Get off the island. Continue reading Origins of Darwin’s Evolution: Solving the Species Puzzle Through Time and Place
Tag Archives: Biogeography
Triassic Life on Land: I love this book
The Triassic is old. This book is new. That is a hard to beat combination.
Continue reading Triassic Life on Land: I love this book
How geology affects your dog’s demeanor and the view from your back yard
Does your back yard slope up, away from your house, or does it slope down?
The likelihood that your yard slopes one way or the other … statistically … depends in large part on what region you live in. (Here I’ll be speaking mainly of the US, but the principle applies broadly.) If you live in New England, your yard is more likely to slope up. If you live in the Midwest/Plains, your yard is more likely to slope down
Continue reading How geology affects your dog’s demeanor and the view from your back yard
Pink Iguanas and Disappearing Islands
It turns out that a recently discovered population of land iguanas on the Galapagos is probably a new species that represents the basal (original) form of Galapagos land iguana. Moreover, this iguana is found in an unexpected place, according to a paper just coming out in the Proceedings of the National Academy of Sciences (PNAS).
And it’s pink.
Continue reading Pink Iguanas and Disappearing Islands
Why the Hobbits of Flores Were Probably Not Broken People
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 enlarged pituitary fossa, and that distinctive primitive features of LB1 such as the double rooted lower premolar and the primitive wrist morphology are consistent with the hypothesis. We find that the null hypothesis (that LB1 is not a cretin) is rejected by the pituitary fossa size of LB1, and by multivariate analyses of cranial measures. We show that critical environmental factors were potentially present on Flores, how remains of cretins but not of unaffected individuals could be preserved in caves, and that extant oral traditions may provide a record of cretinism.
Continue reading Why the Hobbits of Flores Were Probably Not Broken People
Very Large Parks are the Wave of the Future
Across Africa, and to some extent Asia, existing large parks and preserves are being combined into very large parks in order to serve several important functions. One is to make the parks so large that there will be interior areas that are impractical for most poaching or other encroachment. Another is to allow movement of migratory animals into new areas when their populations grow (presumably with some degree of natural culling cycling the process down now and then). Another is to allow a park to always contain a minimal range of a certain habitat even when secular or long term climate variation reduces that habitat. Yet another may be to make the park more attractive to tourism.With animals like tigers, who have relatively low population densities, it is essential to have large contiguous areas in order to have a viable population size both for genetic diversity and to get past periods of decimation by periodic disease or starvation episodes. Continue reading Very Large Parks are the Wave of the Future
Darwin and the Voyage: 11 ~ Elephants and Horses
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. Continue reading Darwin and the Voyage: 11 ~ Elephants and Horses
Darwin and the Voyage: 10 ~ Rheas and the Birth of Evolutionary Theory
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. Continue reading Darwin and the Voyage: 10 ~ Rheas and the Birth of Evolutionary Theory
The Potato and Human Evolution
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. Continue reading The Potato and Human Evolution
Darwin and the Voyage: 09 ~ Fossil Quadrupeds
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. Continue reading Darwin and the Voyage: 09 ~ Fossil Quadrupeds
Darwin and the Voyage: 06 ~ Bugs
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. Continue reading Darwin and the Voyage: 06 ~ Bugs
Are We In The Anthropocene? No.
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. Continue reading Are We In The Anthropocene? No.
Hybrids of Blind Fish Can See
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 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 adaptation (such as sight) has a cost. When a trait that is adaptive is no longer adaptive, individuals with that trait “turned off” should experience an increase in fitness. It may also be the case, however, that such an increase in fitness is so small that it may be irrelevant. This line of thinking needs further investigation and what one finds in such an investigation may vary a lot from system to system. For example, a mutation that simply causes a particular protein to no longer be produced in what would have been a small quantity would save the individual with that mutation the use of a few tens of thousands of amino acids over some fixed period of time. This would have very little fitness value. But if a system is exploitable by a pathogen — such as a receptor site on a cell used by a common virus — turning that gene off may have enormous benefits. But this is a bit of a digression from the research at hand.
Borowsky, in his paper “Restoring sight in blind cavefish,” provides a test case for how we think evolution works. In Mexico, the species Astyanax mexicanus, is known to exist in 29 distinct populations. Genetic studies indicate that the turning off of the sense of sight in these fish has involved a deleterious (as in loss of function) of genes in at least three different lineages, or to put it a different way, sightlessness has evolved three or more separate times in these Mexican blind cavefish.When Borowsky cross breeds some of these cavefish, crossing them between these populations, he gets a certain percentage of fish that have functional, if not fully developed, eyes.This should not be at all surprising. Several different genes are involved in the development of sight, so by cross breeding strains that have experienced mutations in different genes, one would expect a certain number of offspring to have a set of functioning genes sufficient to make the sense of sight develop at least to some extent. When Borowsky breeds the blind cavefish with the non-blind version of this fish (“surface fish”) he gets restoration of the sense of sight in all of the offspring.
F1 hybrids between surface fish and cave fish have smaller eyes than surface fish, but are fully visual, even into adulthood … Thus, one surface allele at each of the population-specific eye loci is sufficient for restoring vision.
This is also expected, although not necessarily inevitable (This depends on the dosage required for each genetically coded step in the development and function of sight).
It seems to me that one could test the hypothesis mentioned above that turning off any fitness-free gene is adaptive. If simple production of unused proteins is costly, the rate at which particular genes are found to be turned off should be correlated with that cost. Perhaps the genes coding for longer proteins, or proteins that are produced more often in a particular system, should be more likely turned off. Or, some measure of the total mass of amino acids turned into proteins when a gene functions, should be correlated to the likelihood of having a gene turned off. At a most basic level, one would need to show that the mutant genes are in fact turned off and are not simply producing a non-functional protein.In short, this study (and others by this and other research teams) demonstrates in empirical reality what is expected from commonly held evolutionary theory. Creationists often cite blind cave dwelling organisms as evidence against evolution, because, they say, it is “devolution.” This point of view is absurd, and relies on a teleological view of, in this case, teleost (bony fish) evolution.
Darwin wrote about cave blindness and disuse, and through various observations notes the potential complexity of the problem:
It is well known that several animals, belonging to the most different classes, which inhabit the caves of Styria and of Kentucky, are blind. In some of the crabs the foot-stalk for the eye remains, though the eye is gone; the stand for the telescope is there, though the telescope with its glasses has been lost. As it is difficult to imagine that eyes, though useless, could be in any way injurious to animals living in darkness, I attribute their loss wholly to disuse. In one of the blind animals, namely, the cave-rat, the eyes are of immense size; and Professor Silliman thought that it regained, after living some days in the light, some slight power of vision. In the same manner as in Madeira the wings of some of the insects have been enlarged, and the wings of others have been reduced by natural selection aided by use and disuse, so in the case of the cave-rat natural selection seems to have struggled with the loss of light and to have increased the size of the eyes; whereas with all the other inhabitants of the caves, disuse by itself seems to have done its work.[On the Origin of Species…, 1859, pp 137-138]
You might be wondering how these fish got into these caves to begin with. I can’t describe the exact process for the fish studied in this paper, but there is a general way in which this can happen. Underground lakes or streams in caves may be connected to each other during less arid periods, in some cases running from the deeps of large lakes that later try up almost entirely. In this way, a continuous population in a river or lake is broken into relict populations that are separate from each other and perhaps living in habitats that are different from the original, continuous habitat, and possibly different from each other as well. Under these conditions evolution’s just gotta happen.
BOROWSKY, R. (2008). Restoring sight in blind cavefish. Current Biology, 18(1), R23-R24. DOI: 10.1016/j.cub.2007.11.023
Did Humans or Climate Change Cause the Extinctions of Pleistocene Eurasian Megafauna?
ï»¿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.
Continue reading Did Humans or Climate Change Cause the Extinctions of Pleistocene Eurasian Megafauna?
After the End Permian Mass Extinction
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. Continue reading After the End Permian Mass Extinction