~ By Raiyaan Bhombal
In 1973, the noted geneticist Theodosius Dobzhansky penned the bold statement in his essay:
“Nothing in Biology makes sense except in the light of evolution”
But sometimes, when the questions being explored are at the cutting edge of scientific research, the light of evolution casts shadows that are hard to decipher! However, before we delve into these questions, lets grasp an elementary understanding of the subject at hand.
For several millenniums, the belief of creationism, wherein the genesis of the universe and life is credited to supernatural acts by a divine entity, was shared amongst most scientists; that is until Charles Darwin challenged this thought in his book “The Origin of Species” published in 1985. Different living beings within a species have slightly different traits from each other. Some of these traits may make an organism better suited for survival in their environment than other traits. Because resources are limited in nature, organism with favourable heritable traits will survive longer and hence their chances of reproducing to leave more offspring is higher. These offspring have slight variation too, and the survival-of-the-fittest mechanism continues. Over time, sufficient variation results in a generation with indistinguishable characteristics from their ancestors, giving rise to new species of organisms. This is Charles Darwin’s Theory of Evolution by Natural Selection and is a fundamental concept in our study of the natural world, supported with a fair amount of evidence. Despite this, it is widely disputed and innumerable opposing articles and notions have risen since 1985.
As fundamental as this theory sounds, the challenge of evolutionary biology is to explain the origin and function of certain unique traits in organisms, and this often gives rise to a myriad of questions.
Q) Why do giraffes have such long necks?
It may appear obvious that the giraffe’s neck, which can grow up to 2 metres in length, is a result of natural selection that gives the animal exclusive access to the higher branches of a tree, avoiding competition for food with other animals that cannot reach up to these heights. However, in the 1990s, some biologists observed that giraffes did not use their long necks to browse at heights. In fact, when competition was most fierce, the females spent up to half their time with their necks held horizontally rather than exploiting their height advantage. These biologists then suggested that the long neck is used as a weapon primarily by males; Male giraffes have an extremely thick skull that can break a vertebral column when used for fighting, helping the male assert dominance over other males in “neck-fights” to gain access to the females. To corroborate this idea, it has also been found that the males that reproduce most tend to be the ones with the longest, strongest necks. But why do female giraffes have long necks too? Although this can be a result of genetic correlation between the sexes, the original ideology also comes into play: the long neck size is indeed used to raze at heights when the lower branches are fully grazed. Fortunately, one explanation does not exclude the other. Some biologists have also suggested that it helps the animals spot predators and that its increase surface area assists the regulation of body temperature. However, it is difficult to say which of these suggestions has had a greater influence on this evolutionary trait and this uncertainty looks set to keep researches busy for a while.
Q) How did zebras get their stripes?
Whether you’re watching them in the Madagascar movies or National Geographic, the most salient feature on zebras are the contrasting stripes on their coats. However ostentatious these stripes may be, they actually have a purpose, but putting a finger on what exactly lead to the zebras having stripes on them is where the conundrum lies. One of the most fascinating theories amongst the many is that these stripes are used to disrupt the predator’s perception. Not only do striped animals appear larger than they actually are, which can confuse the predator about when and where to attack, but they also disrupt the predator’s perception of the speed and direction of its prey. Simulations have shown that the stripes of a zebra can produce two optical illusions, both of which reverse the perceived direction of movement. The first illusion is the stroboscopic effect, like the one seen in rapidly revolving objects such as a fan. In certain natural light conditions, these objects can give the impression of turning slowly, standing still or even of turning in the opposite direction! The second is the barber-pole effect, in which the diagonal stripes seem to drift upward as the pole rotates. When zebras are in motion, both these illusions coupled together disrupt the predator, who are thus inclined to misinterpret the movement of the zebra and launch their attacks inaccurately. Some other theories about these stripes are: they enable individual members of the group to recognize each other, they offer camouflage in tall grass, they offer camouflage at night, they serve to dissipate heat, they deter flies from landing on the animals, etc.
Q) Why do men have nipples?
It is a common fact that the teats on a woman are used by infants during lactation (the suckling of an infant for breast milk), however, their function in men isn’t as clear as they do not breastfeed. One school of thought suggests that all human embryos start out as female; the female sex is the basic form from which the male sex will differentiate itself. In simpler words, during the first several weeks of pregnancy, male and female embryos follow the same blueprint, which includes the development of nipples. The first male hormones only appear seven to eight weeks into pregnancy, whereas the nipples are usually present by the sixth week. On the seventh/eighth week of gestation, the Y chromosome (the male chromosome) begins to induce changes, such as the development of the testes, which marks the beginning of the fetus’ differentiation into a male. We know that natural selection is responsible for eliminating less favourable traits in species, then why has natural selection not eliminated nipples from men? The reason for this is because the nipples do not impose any disadvantage on men, and hence it is not a priority for evolution to select against it. These traits are called vestigial and other examples of it are wisdom teeth and the appendix.
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