Lamarck maybe because the more nutritious leaves
Lamarck and Darwin both believed that giraffes developed long necks because that is what they use to consume the leaves high above trees. Lamarck’s theory is that “because their (giraffes) forebears were continually stretching to reach the higher leaves in trees. The desire to reach higher leaves led to longer necks, and later on, the giraffe’s offspring inherited that physical trait”(Natural History, 2005, p. 46). Darwin disagrees with Lamarck when his theory of natural selection stated that the giraffes with longer necks outlived the ones with shorter necks maybe because the more nutritious leaves were at the higher parts of trees.
However, when Lamarck said that unused organs shrivel until they disappear,(Natural History, 2005, p. 46) Darwin was at a loss since his theory of natural selection cannot explain regressive evolution and he finally succumbed to Lamarck’s use it or lose it principle. Darwin, regardless of how great a scientist he is, is not infallible. Robert Simmons has recently voiced out a contradictory view of both Darwin and Lamarck’s theory of why giraffes have long necks. Simmons believes that competition for mates and not stretching for treetop food is what drove the evolution of necks.
According to his observations, when male giraffes battle for mates, they swing their necks of over 6 feet long and weighs over 200 lbs. The momentum of these swings are often lethal, therefore, it is only natural that the victor is the one who possesses the longest and biggest neck. He goes on to say that if the competition for food is what spurred the elongation, then you would expect giraffes to eat the leaves from tall acacia trees rather than grazing on low shrubs. (Discover, 1997, p. 14)
If Simmons’ theory disproves Lamarck’s conclusion that the stretching of the neck was due to food competition, then it can be said that the principle of “Use it or Lose it” can be disproved. To know if whether this principle is still steadfast, we have to consider both sides of the spectrum. The main proponent of Lamarck’s use it or lose it theory is the neutral-mutation hypothesis. According to this hypothesis, “genes controlling the development of unnecessary structures become effectively neutral.
Once the genes neither enhance nor hinder the organism’s survival, the forces that once maintained those genes in good working order no longer operate. The genes accumulate mutation that impair their function, and so the unnecessary genes degenerate” (Natural History, 2005, p. 47). Careful analysis of the use it or lose it scenario shall lead one to believe that if an organ is not anymore needed, it shall degenerate and sooner or later entirely disappear without any effect on the organism except for the loss of an unnecessary part.
A group of scientists that holds a contrary view believes that the loss of one part is due to regressive evolution and not because it is not used. This group espouses the hypotheses that the loss of one organ enhances other organs, in cave fishes for example – “the loss of eyes somehow enhances the efficiency of neural processing or reshapes the fish’s morphology or physiology to better suit a life of total darkness” (Natural History, 2005, p. 47). The main problem faced by this group of scientists is that they need to account for an advantage for the loss of the organ.
The scientists have come up with an answer to their problem, pleiotropy. Pleiotropic effects are the multiple seemingly unrelated characters caused by a single gene. An example of pleiotropy, and the most documented case at that, is the gene associated with sickle cell diseases. People who have this gene suffer from chronic anemia, extreme pain and organ damage but are more immune to malaria because the parasite that causes malaria cannot thrive in blood cells that carry this gene.
The malaria resistance conferred by the sickle-cell gene is a pleiotropic effect, this gene although harmful persists in African communities where there are high incidences of malaria (Natural History, 2005, p. 47). Pleiotropy is now being used to prove why cave-fish lose their eyes and eventually disprove that if you do not use an organ you will lose it. Scientific evidence is now available that tends to prove that cave-fish lose their eyes not because it is not needed and its loss shall not be advantageous or disadvantageous to the fish but because it is evolving.
Borrowsky and Wilken discovered that a gene that controls metabolic rate is closely related to eye development, such that a genetic mutation to improve metabolism can also harm eye development (Natural History, 2005, p. 48). Another group of scientists that came up with evidence to support pleiotropy discovered that a gene called Hedgehog (Hh) was responsible for the development of the size of the eyes of the fish together with its teeth, tastebuds, anterior part of the brain and other craniofacial structures.
They have determined that the development of the eyes was inversely proportional to the number of taste buds, thus the smaller the eyes the greater the number of taste buds and the better is its sense of taste. Another effect of the eyeless sockets is that the bones of the face fill up the empty spaces causing deformity in the fish’s skull, a closer inspection of this showed that due to this deformity the width of the olfactory pit was increased by 13% which likely results in the fish’s enhanced sense of smell.
Finally, there is also evidence that blind people develop above average abilities in specific tasks related to hearing or to touching which can also be explained by pleiotropy (Natural History, 2005, p. 49). In conclusion, the Use it or Lose it principle seems to have lost its appeal among scientists. Gradually, scientists are now discovering new ways to counter this argument and the results are astounding. Evidence such as those enumerated above have already disproved its application to cave-fish and probably eventually, it shall lose its significance in the field of evolution as well.