Something is said to be symmetrical when the left and right halves match each other as in a mirror image on either side of a central line. Nature is replete with this kind of symmetry. Our tabby cat, Nina, in the photo above, shows off her wonderfully symmetrical structure and facial markings.
For most animal species the body shape is bilaterally structured, akin to mirror symmetry. Although there are animal species, such as jelly fish, corals and anemone, whose structural symmetry is radial rather than bilateral, they are in a minority. The human body too is bilaterally structured – although the internal organs are not necessarily symmetrically distributed.
This southern tree agama (in our garden) displays its bilateral symmetry on either side of an imaginary central line. Although to any observer the right side and the left side are pretty much symmetrical (although not as perfectly so as in a computer-created drawing for instance) it is interesting that in certain aspects animals may be functionally asymmetric. For example, in humans at least, most individuals are right- or left-handed, and the hemispheres of the brain have functional asymmetry.
This elephant (at Addo Elephant Nation Park) shows off its symmetrical structure with the trunk and mouth on the central bisecting line. Interestingly, the majority of female elephants at the Addo park lack tusks.
This general tusklessness is thought to have resulted from the long history of killing of elephants for their tusks. In isolated populations this selective killing resulted in the existence of a higher than normal percentage of tuskless elephants among survivors. With only a small population left before elephants became protected at Addo, the unnatural selection resulted in a genetic preponderance for tuskless elephants. A similar scenario has been observed at Gorongoza National Park in Mozambique. For fascinating background information on this phenomenon see https://www.earthdate.org/tuskless-elephants
One of the most spectacular displays of bilateral symmetry can be seen in the long and elegant horns of male kudu antelope. This one is browsing near the roadside at Addo Elephant National Park.
Iconic in South Africa is the Springbok. Photographed in the Central Kalahari Game Reserve in Botswana, this springbok ram displays his symmetrical horns and facial markings. Springboks once roamed South Africa in vast migratory herds especially in the Highveld and Karoo regions. Sadly though, the last great migration in the Karoo took place at the end of the 1800s. Farming, fencing and hunting were major factors in the dramatic decline in the wild herds of springbok. Nevertheless, to this day trophy hunters include springboks in their list of targets.
One of the stranger -looking antelopes is the red hartebeest. I photographed this one at the Mountain Zebra National Park. Both male and females hartebeests have horns, with the males generally having heavier horns than the females do.
This Cape mountain zebra (at the Mountain Zebra National Park) shows how the complex pattern of stripes tends towards being symmetrical, at least on the rump and forehead. Each zebra has a unique stripe pattern with no two zebras having identical stripes.
Like most creatures, butterflies are structured with bilateral symmetry, but also the patterning on their wings is almost perfectly symmetrical, as can be seen on the open wings of this garden inspector butterfly, which I photographed as it basked in winter sunshine in our garden.
These foam grasshoppers show their obvious symmetry. As they approach through the grass they resemble an advancing army.
Wings spread to dry after a bout of fishing, this white-breasted cormorant displays the almost perfect symmetry of its wings. Obviously symmetry in birds is essential for flying efficiently, as it is for walking and running in mammals and other animals.
It is not only animals that are structured bilaterally as evidenced by this flower of a Mackaya bella. The shape and stripes help guide pollinating insects into the throat of the flower. Additional guiding patterns on these flowers that insects can detect can only be seen by the human eye under ultra-violet light.
Flowers are the fertilization point for plants so they have evolved to attract pollinators, with some flowers adapted to attracting specific species of pollinators. Flowers that display bilateral symmetry are more likely to have specialised signals for specific pollinators than flowers with radial symmetry.
The structure of these gerbera flowers displays radial symmetry – the petals are arranged symmetrically around a central point. More flowers display radial symmetry than bilateral symmetry. Bilateral symmetry in flowers evolved in relation to attracting specific pollinators and developed from earlier radially symmetrical forms (for more see Symmetry in Organismal Biology).
These gazanias (probably hybrids, which I photographed in the Western Cape), are a spectacular example of flowers with radial symmetry.
A more complex variant of radial symmetry is displayed by this wild iris (Dietes grandiflora).
Also displaying radial symmetry are the petals of this Freesia laxa.
The buds and the open flowers of the yellow everlasting (Helichrysum cooperi) also exhibit radial symmetry. In our garden these attractive grassland plants self-seed to reliably produce a new crop of plants that flower during the summer months.
In contrast, here is the bilaterally symmetrical flower of the tropical spiderwort (Commelina benghalensis) attracting a hoverfly, which of course also exhibits bilateral symmetry.
This rather striking flower decorated with rain drops also exhibits bilateral symmetry. I have no idea of the identity of this exotic plant that cropped up in our garden at one time but has since disappeared.
Leaves of plants are also structured with bilateral symmetry, even though the symmetry may not be exact. These are leaves of the wild mulberry (Trimeria grandifolia ), photographed in our garden.
Prominently symmetrical in an unusual set of matching pairs and with each leaf being bilaterally symmetrical too, are freshly sprouted leaves of the toad tree (Tabernaemontana elegans), which is deciduous in our garden.
The fruit of the toad tree (Tabernaemontana elegans) appears in symmetrical pairs. These were the first fruits on this young tree, which we planted only last year. I hoped to see the fruits grow and eventually bear seed, but this was not to be. Something ate the undeveloped fruit the day after this photo was taken!
And I end off with a photo of an African buffalo at Addo Elephant National Park, displaying not only the bilateral symmetry of the curved horns, but also the symmetry of four muddy ‘boots’. The ‘boots’ match the glistening mud on the forehead and crown as the buffalo walks away from a waterhole after an early morning drink.
Posted by Carol