October 25, 2018 | David F. Coppedge

Three More Designs that Defy Evolution

Darwinian natural selection sounds convincing until you look at the details of extraordinary designs in nature.

Dandelion Seeds

A study in Nature shows that the lowly dandelion seed uses an “extraordinary” flight technique that was previously unknown. Called a “separated vortex ring,” the mechanism literally sucks the seed and its parachute up into the air. Jeremy Rehm, commenting on this in Nature, calls it an “‘impossible’ method never before seen” but that might actually be common in the living world. See the short embedded video in Rehm’s article, or on YouTube, where scientists at the University of Edinburgh show how it works. “Perhaps one day, even human technologies could be designed to fly as efficiently as the mighty dandelion seed,” the narrator says of this “completely new type of flight.

The mechanism depends on the precise spacing, length, and mass of the filaments on the parachute, called a pappus. Surprisingly, the open-air parachute creates more drag than if it were a solid disk, and air flow through the filaments causes a low-pressure vortex above the pappus to suck the parachute up, giving if lift and simultaneously stabilizing its orientation. Nature says, “a rare combination of size, mass, shape and, crucially, porosity for the pappus to generate this vortex ring.”

Mantis Shrimp

The amazing mantis shrimp is back in the news. New Scientist reporter Leah Crane tells how the googly-eyed arthropod packs a wallop strong as a .22 bullet with its club. Instead of big biceps, “it has arms that are naturally spring-loaded, allowing it to swing its fistlike clubs to speeds up to 23 metres per second.”

Researchers at Nanyang Technological University in Singapore examined the saddle-shaped device on the limb that stores elastic energy, and watched what happened when they tweaked its shape.

Miserez and his colleagues used a series of tiny pokes and prods, as well as a computer model, to examine exactly how the shrimp’s saddle holds all that energy without snapping. They found that it works because of a two-layer structure. The top layer is made of a ceramic material similar to bone, and the bottom is made of mostly plastic-like biopolymers.

When the saddle is bent, the top layer gets compressed and the bottom layer is stretched. The ceramic can hold a lot of energy when it is compressed, but is brittle when bent and stretched. The biopolymers are stronger and stretchier, so they hold the whole thing together.

Both the spring-loaded device and the resilient material in the club are necessary for the powerful force of the mantis shrimp’s punch, which is strong enough to shatter the hard shells of their prey. And that’s just one of the irreducibly complex mechanisms in this animal’s repertoire. It is also the only animal known that can sense and utilize circularly polarized light (31 March 2008). Crane mentions that scientists at MIT are considering imitating the mantis shrimp’s firepower for human applications.

Human Brain

Clare Wilson announces in New Scientist, “Your brain is like 100 billion mini-computers all working together.” Mark Harnett at the Massachusetts Institute of Technology in Cambridge installed microscopic electrodes into living nerve cells that had been removed during surgery on epilepsy patients. What he found was astonishing.

Credit: Illustra Media

Each of our brain cells could work like a mini-computer,” Wilson writes, “according to the first recording of electrical activity in human cells at a super-fine level of detail.” Consider just one neuron among the hundred billion inside your skull:

Each neuron may have about 50 dendrites, and each dendrite has hundreds of synapses, or connection points with other neurons. It’s signals running across these synapses and into the dendrite that make it more or less likely that the dendrite itself will fire an electrical signal along its length.

The number of ion channels per dendrite is smaller in humans than in mice, Wilson explains. But this is good; it gives the synapses at the ends of the dendrites more opportunity for synergy. The dendrites, therefore, “collectively determine the final ‘decision’ on whether the main branch should fire.” That’s happening right now as you read this article.

If Darwin were here, his probable reaction is depicted in Brett Miller’s cartoon:

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