Excerpt from chapter 5

Genesis and Genes is now available in Israel, the UK and the USA. It is expected in South Africa in January 2013. In the meantime, I intend to post a number of sample passages. Here is an excerpt from chapter 5.

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Edward Tyson was born in Somerset in 1650, and was educated first at Oxford and later at Cambridge, where he received his medical degree in 1677. Tyson moved to London where he practised as a doctor and also performed anatomical observations and dissections, publishing much of his work in the Philosophical Transactions of the Royal Society, having been elected as a fellow in 1679. As one of the leading physicians of the time (he became a Fellow of the Royal College of Physicians), Tyson was appointed physician and governor of the Bethlehem Hospital in London in 1684. This was an institution for the insane whose character at the time of Tyson’s appointment gave us the word bedlam as a synonym for pandemonium, from the common pronunciation of its name. This was the first asylum for the insane in Britain (the first European institution was founded in Granada, Spain). Asylum, with its connotations of protection and care, is a misleading term. The inmates were abused and were treated as a source of entertainment, with Bedlam becoming a place of amusement for fashionable people to visit, rather like a zoo. Tyson changed this state of affairs, introducing reforms such as employing women nurses instead of the male nurses who were little more than jailers. He also established a fund to provide clothing for the poorer inmates.

Tyson is regarded as the founder of modern comparative anatomy, which looks at the similarities and differences of physique of different organisms. His most important dissection, in the context of our discussion, took place in 1680, when a hapless porpoise swam up the Thames and ended up with a fishmonger who sold it to Tyson for seven shillings and sixpence (a sum recouped by Tyson from the Royal Society). Tyson dissected the “fish” at Gresham College, with Robert Hooke in attendance to make drawings as the dissection proceeded, and was astonished to discover that the animal was in fact a mammal, with an internal structure very similar to that of the quadrupeds (animals with four feet) that lived on land. In his book Anatomy of a Porpess, published later that year, he presented his discovery:

“The structure of the viscera and inward parts have so great an Analogy and resemblance to those of Quadrupeds, that we find them here almost the same. The greatest difference from them seems to be in the external shape, and wanting [i.e. lacking] feet. But here too we observed that when the skin and flesh was taken off, the fore-fins did very well represent an Arm, there being the Scapula, an os Humeri, the Ulna, and Radius, and bone of the Carpus, the Metacarp, and 5 digity curiously jointed…”

Tyson performed many other famous dissections, including that of a young chimpanzee (mistakenly described as an orang-utan) which was brought to London as a pet by a sailor in 1698. The young ape was ailing. Tyson studied its appearance and behaviour while it remained alive, and dissected it as soon as it died, this time with William Cowper assisting with the drawings. They published their findings in the splendidly-titled Orang-Outang, sive Homo Sylvestris: or, the Anatomy of a Pygmie Compared with that of a Monkey, an Ape, and a Man. The 165-page, heavily-illustrated volume showed that human beings and chimpanzees were built to a very similar body-plan. At the end of the book, Tyson listed the most significant features of the chimp’s anatomy, noting that 48 of them resembled the equivalent human features more than they did those of a monkey, while 27 more closely resembled those of a monkey than those of a human. He concluded that a chimpanzee resembles a human more than it resembles a monkey. This was a turning point in the quest to classify the relationships between organisms on the basis of anatomical resemblance.

Since Tyson’s time, numerous examples of similarities in bone structure in different organisms have been discovered. The classic example – presented in biology textbooks, television documentaries, magazine articles and museum displays – is the forelimbs of vertebrates. [Vertebrates are creatures that possess a spinal column. It is a category that includes mammals, birds, reptiles, amphibians, and fish.] Thus, although a bat has wings for flying, a porpoise has flippers for swimming, a horse has legs for running, and a human has hands for grasping, the bone patterns in their forelimbs are similar. Take, for example, a human hand and a dog’s forepaw. There is one bone in your upper arm, between your shoulder and elbow: the humerus. Between the elbow and your wrist, there are two bones: the radius and the ulna. Then come the carpals of your wrist, the metacarpals (tubular bones between the wrist bones and each of the forelimb digits) and the phalanges (the skeletal parts of the fingers). A very similar arrangement exists in the dog’s forepaw.

In time, the similarity between the bone arrangement in the flipper of the porpoise and land-dwelling animals described by Edward Tyson came to be known as homology. The term was coined by Richard Owen (1804-1892), one of the leading biologists of the nineteenth century. He is best remembered for coining the word dinosaurian (meaning terrible reptiles) and as the driving force behind the establishment of the British Museum of Natural History in London. He is also remembered as an outspoken opponent of Charles Darwin’s theory of evolution by natural selection. In the late 1840s, Owen coined the term analogy to describe functional similarity and homology to describe structural similarity. Let’s take a moment to appreciate the difference between the two. In biology, similar features come in two varieties: functional and structural. For instance, bird wings and insect wings are both used for flying. Both types of wing function in the same way: the wing is shaped like an aerofoil, producing lower air-pressure on its upper side and higher air-pressure on the underside, thus creating lift. Flapping the wings provides forward thrust. But the internal structure of birds’ wings is very different to that of insects. A bird wing consists of flesh, supplied with nourishment and oxygen by a network of blood vessels. Structural stability comes from bones in the wing. Insect wings contain no bones or blood vessels. They consist of a thin membrane stretched tightly around a network of wiry structures, like a kite. So bird wings and insect wings serve the same function but have a different structure. This concept works in reverse too. As we mentioned earlier, the structure of the flipper of a porpoise is very similar to the structure of a bat’s wing i.e. the arrangement of bones is similar. But these appendages have very different functions. The porpoise uses its flipper to swim, while the bat uses its wing to fly. The similarity is structural, not functional. In the case of the forelimbs of humans and dogs, we saw that the arrangement of the bones is similar. But although the bone pattern is the same, the individual bones are quite different in shape, function and other respects. Dogs cannot grasp objects with their digits or oppose their thumb to the rest of the toes. Human hands are not made to walk on for any length of time. The similarity is one of homology (structure or pattern), not analogy (function).

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