Human children: please take note of the behavior of prebirth zebra finches
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Last week, the Arkansas state House of Representatives passed a bill that would amend state education law to allow teachers in public schools to teach creationism as “a theory of how the earth came to exist.” As it stands, the act promotes blatantly unconstitutional behavior as made clear by a precedent set in a 1982 case involving the Arkansas Board of Education. Despite that, the bill passed 72-21, and it already has a sponsor in the state Senate.
The body of the bill is mercifully short, consisting of two sentence-long amendments to the existing Arkansas code:
A teacher of a kindergarten through grade twelve (K-12) science class at a public school or open-enrollment public charter school may teach creationism as a theory of how the earth came to exist.
This section is permissive and does not require a teacher to teach creationism as a theory of the earth came to exist.
But those two sentences are enough to land teachers and their local school system in a world of trouble, in that the permission given runs afoul of a lot of legal precedent. In a key case that involved Arkansas itself, McLean V. Arkansas Board of Education, a group of plaintiffs banded together to challenge a state law that mandated the teaching of “creation science” in public schools. The judge in that case correctly recognized that creation science was actually religious in nature, and it therefore violated the constitution’s prohibition against the establishment of state religion.
We have an extensive collection of fossils from the lineages that produced us humans. A large number of Australopithecus and early Homo skeletons track the transition to bipedal walking and the appearance of features that mark our present anatomy. But it’s much harder to figure out what led to the mental capabilities—complex language, the near-constant use of tools, and so on—that help set humans apart.
Much harder—but not entirely impossible. Remains of skulls can help us figure out the likely cranial capacity of extinct species. And the brain actually leaves its mark on the interior of skulls, allowing some aspects of the brain’s anatomy to be pieced together. Now, an international team has done this sort of analysis on a set of Homo erectus from a critical point in our species’ past. They have found that some earlier brain species persisted well into the history of our genus Homo, but that didn’t stop those ancestors from migrating out of Africa.
How do you figure out what a brain once looked like? You need a reasonably intact skull, which is relatively rare, given the fragility of the bones. Once the skull is reconstructed, it’s possible to make what’s called an “endocast” of the interior of the skull, capturing the details of its features, including where it conformed to the underlying brain. In some cases, endocasts form naturally during the deposition of material around a fossil. They could also be made after discovery and now can be done virtually thanks to our ability to scan and reconstruct 3D volumes.
Deep in Switzerland’s Lake Zug swims a microorganism that has evolved a strange way to “breathe.” A team of researchers discovered a novel partnership between a single-celled eukaryote—an organism with a clearly defined nucleus holding its genome—and a bacteria that generates energy for its host. But instead of using oxygen to do so, it uses nitrate.
“This is a very weird, [newly discovered] organism,” said Jana Milucka, a biologist at the Max Planck Genome Center in Cologne and senior author on the resulting paper, published in Nature in early March.
The team named the bacteria Candidatus Azoamicus ciliaticola, meaning “nitrogen-friend that lives inside a ciliate.” Its partner, the ciliate, is a microorganism that moves around using cilia, tiny hair-like protrusions outside their cell walls. The host organism is part of a group of ciliates called Plagiopylea.
Ancient DNA has revolutionized how we understand human evolution, revealing how populations moved and interacted and introducing us to relatives like the Denisovans, a “ghost lineage” that we wouldn’t realize existed if it weren’t for discovering their DNA. But humans aren’t the only ones who have left DNA behind in their bones, and the same analyses that worked for humans can work for any other group of species.
Today, the mammoths take their turn in the spotlight, helped by what appears to be the oldest DNA ever sequenced. DNA from three ancient molars, one likely to be over a million years old, has revealed that there is a ghost lineage of mammoths that interbred with distant relatives to produce the North American mammoth population.
Mammoths share something with humans: like us, they started as an African population but spread across much of the planet. Having spread out much earlier, mammoth populations spent enough time separated from each other to form different species. After branching off from elephants, the mammoths first split into what are called southern and steppe species. Later still, adaptations to ice age climates produced the woolly mammoth and its close relative, the North American mammoth, called the Columbian mammoth. All of those species, however, are extinct, and the only living relatives are the elephants.
What are the key differences between modern humans and our closest relatives, the Neanderthals and Denisovans? For the Neanderthals, there doesn’t look to be any sort of obvious difference. They used sophisticated tools, made art, and established themselves in some very harsh environments. But, as far as we can tell, their overall population was never particularly high. When modern humans arrived on the scene in Eurasia, our numbers grew larger, we spread even further, and the Neanderthals and Denisovans ended up displaced and eventually extinct.
With our ability to obtain ancient DNA, we’ve now gotten a look at the genomes of both Neanderthals and Denisovans, which allows us to ask a more specific question: could some of our differences be due to genetics?
The three species are close relatives, so the number of differences in our proteins are relatively small. But a large, international research team has identified one and engineered it back into stem cells obtained from modern humans. And the researchers found that neural tissue made of these cells has notable differences from the same tissue grown with the modern human version of this gene.
Dire wolves had a burst of newfound fame with their appearance in Game of Thrones, where they were portrayed as a far larger version of more mundane wolves. Here in the real world, only the largest populations of present-day wolves get as large as the dire wolf, which weighed nearly 70 kilograms. These animals once shared North America—and likely prey—with predators like the smilodon, a saber-toothed cat. Prior to the arrival of humans, dire wolves were far more common than regular wolves, as indicated by the remains found in the La Brea tar seeps, where they outnumber gray wolves by a factor of about 100.
Like the smilodon and many other large North American mammals, the dire wolf vanished during a period of climate change and the arrival of humans to the continent, even as gray wolves and coyotes survived. And with their departure, they left behind a bit of a mystery: what were they?
A new study uses ancient DNA from dire wolf skeletons to determine that they weren’t actually wolves and had been genetically isolated from them for millions of years.
Given the unusual attention granted to turkeys this week, let’s talk dinosaurs. Today’s birds are, of course, descendants of the only branch of the dino tree that made it through the end-Cretaceous mass extinction. In the dinosaurs’ halcyon days, the early birds were a bit different, still retaining teeth and foreclaws among some subtler anatomical differences with their modern descendant. A new fossil find reveals an unexpected bird from that time—one with a whopping-great, toucan-like beak.
The fossil, named Falcatakely forsterae, comes from late Cretaceous rocks in Madagascar. Many of the early bird fossils we’ve discovered so far come from older, early-Cretaceous rocks in China, with the timeframe between then and the end-Cretaceous extinction more of a question mark. The new fossil is a nicely preserved head of a crow-sized bird with a strikingly long, tall, and narrow beak.
The early Chinese bird fossils don’t show much diversity in beak shape. That’s a big contrast with modern birds, which have a wild variety of beak shapes befitting their many different ecological niches. Pelicans, woodpeckers, and parrots have very different diets that require a beak adapted to the job. It had been thought that enlarged beaks may not have been possible until some anatomical shifting in the parts of the skull took place, meaning that the early birds were simply limited. But the new find shows that wasn’t entirely true. This species could have inhabited an ecological niche that was empty after the extinction—until a more modern bird drifted back into it much later.