Floats like a butterfly, swims like a bee, according to reports in BBC News 18 February 2016, Science Shots 19 February 2016 and Journal of Experimental Biology, doi:10.1242/jeb.129205. The sea butterfly Limacina helicina is a tiny sea snail, with a gelatinous body encased in a calcium carbonate shell, but instead of a foot it has two wing-like appendages projecting from the shell. Rather than crawl along the sea floor, it swims in the water column using the appendages.
A group of scientists from Georgia Institute of Technology and Johns Hopkins University studied the swimming movement of sea butterflies using high speed video recordings and analysed the flow of the water around them as they swam. This was quite a challenge as the creatures are only 4-14mm in length.
The results showed that, rather than using the wings like paddles, as most swimming creatures do, the sea butterflies rotate their wings in a figure of eight pattern, creating vortices in the water, in the same way that insects fly by creating vortices in the air around their wings. Part of the swimming stroke involves a manoeuvre called the ‘clap-and-fling’, where the snail brings the two appendages together and rapidly pulls them apart.
David Murphy, a mechanical engineer at Johns Hopkins University, explained to the BBC: “This sucks fluid into that V-shaped gap as the wings open up, and creates tiny vortices at the tips of each of the wings. Those vortices are useful in generating extra lift”.
Snails and insects are considered to be separated by 550 million years of evolution but because the sea butterfly and small insects have to move in similar environments, the researchers concluded “Limacina helicina and tiny insects thus represent a remarkable evolutionary convergence of locomotion techniques employed by dissimilar animals”.
Editorial Comment: The concept of convergent evolution is the idea that unrelated creatures can evolve similar structures and functions because they inhabit the same environment, or face the same challenges to stay alive. In this case, tiny creatures that have to move through fluids (air or water) have evolved the same wing structure and movement. Air is considered a fluid because it flows, and for a small insect with tiny wings air is quite thick.
However, at the risk of being boring, let us repeat that simply being surrounded by a fluid will not change the genes of a non-flying insect or snail to evolve them into creatures with wings and nervous system control which moves the wings in a way that creates vortices. A fluid environment will simply eliminate any creatures that can’t already fly through air or water.
The concept that unrelated creatures can be similar by convergent evolution is just wishful thinking, and is an admission that all evolutionary trees, which are based on the concept that similar creatures are genetically related, do not explain the diversity of living creatures in the world. It is time to get back to the Biblical principle that created kinds (whether animal or plant) are unique combinations of non-unique structures and functions, well designed to fit the environments they were created to live in. (Ref. molluscs, design, locomotion, swimming, flying)
Evidence News vol. 16, No.4
9 March 2016
Creation Research Australia