Wednesday November 26, 2014

Evolution has much to teach us


Scientists at Yale University published a fascinating study last week in Proceedings of the National Academy of Science that may have applications in the field of biomimetics, also referred to as biomimicry.

The researchers were able to create a structural change in butterfly wings that shifted their colour from brown to violet using “artificial” selection in less than a year and only six generations of the species Bycylus anynana. I don’t like the term artificial selection because it implies humans and our activities are somehow apart from, outside of or above nature, but that is a digression that could be the topic for its own column.

Biomimetics is the imitation of models, systems and elements of nature for the purpose of solving human problems. One of my favourite examples of this is the invention of Velcro. The Swiss inventor of Velcro was inspired to create it after returning from a hike covered in burrs. On inspecting the seed-bearing pod under his microscope, he noted it was covered in tiny, sturdy hooks that allowed them to securely attach themselves to the tiny loops of fabric in his pants. Today, Velcro is ubiquitous, often taking the place of laces, zippers, buttons, elastics and has myriad other uses.

Biomimetics has been used in everything from aerospace to communications technology to architecture. One beautiful example is the 2003 Gherkin Tower in London modelled after the Venus flower basket sponge. With its lattice-like exoskeleton and bullet shape the sponge efficiently disperses the stresses of strong water currents as the tower does high winds.

Evolution has an amazing capacity for engineering optimal solutions to problems such as transporting seeds to new fertile growing grounds, keeping sponges stable in strong currents and the light-refracting structure of butterfly wings, which frequently provides the fragile creatures with excellent camouflage. The light refracting properties of butterfly wings has been used in the past to design better digital displays. Of course, evolution also has the luxury of virtually limitless time.

“Today, materials engineers are making complex materials to perform multiple functions,” said Hui Cao, a professor of applied physics who worked on the project. “The parameter space for the design of such materials is huge, so it is not easy to search for the optimal design. This is why we can learn from nature, which has obtained the optimal solutions in many cases via natural evolution over millions of years.”

I’m not entirely sure if Bicyclus anynana would want to be violet instead of brown, but one of the reasons the researchers chose Bicyclus anynana is because its cousin species have made the transition twice independently.

There are various mechanisms that produce colour in nature. In the case of the Bicyclus genus of butterfly it is the structure of the scales on the wing that refract light. By producing thicker scales through selective breeding in such a short time, the Yale team showed butterfly populations harbour high levels of genetic variation regulating scale thickness that allow them to react very quickly to changing selective pressures.

Another great example of this is the urban peppered moth. Before the industrial revolution 98 per cent of the species Biston betularia had a light, mottled colouring that provided good camouflage against predators, namely birds. The remainder of the population had uniform dark colouring. By the end of the industrial revolution the population distribution was reversed with only five per cent retaining the original light, mottled look.

It has been posited that as the light surfaces the moths tended to rest on became darkened by soot and the death of light coloured lichens due to acid rain, the dark ones gained the advantage of camouflage the light ones had originally enjoyed.

Evolution “skeptics” tried to discredit this classic example of evolution in action back in the late 1990s, mainly by attacking bird predation as the selective pressure for the shift in colour. The example stands up to scrutiny, however, both through observation of population distribution in more and less polluted woods as well as experimental data.

In any event evolution never stops teaching us, both about the world in general and how we can harness its awesome diversity in our human endeavours.



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