Charles Darwin
Page 29
Furthermore, it has been suggested that dinosaurs, like their non-dinosaur reptilian ‘cousins’, had a heart and circulatory system (though this has not been proved). If so, this would have facilitated the rapid transfer of heat from the core to the periphery, making them even more susceptible to cold.
Were there any active steps which dinosaurs could have taken in order to keep warm? The answer is no, other than by the temporary expedient of involuntary shivering, or actively running around so as to generate heat within the musculature.
The consequences of hypothermia
In the phase of mild hypothermia the dinosaur’s musculature would become uncoordinated, resulting in slow and sluggish movements, and stumbling. And as hypothermia progressed and the creature’s cellular metabolic processes began to fail, it would become confused and disorientated, death being the end result.
Is there evidence of a fall in the Earth’s temperature at about the K-T Boundary?
There is scientific evidence that during the Cretaceous period, Earth experienced episodes of intense cold, and that one of these so-called cold events occurred during the valanginian era – which immediately preceded the K-T Boundary.6 However, it is not known whether these ‘cold events’ were confined to the Arctic region, where the studies were conducted, or if they were worldwide phenomena?
What could have caused a drastic reduction in the Earth’s temperature?
Asteroid collision
In 1977 US geologist Walter Alvarez was studying limestone rocks in the vicinity of Gubbio, a village of northern Italy. Here, sandwiched between rocks representing the end of the Cretaceous and those representing the beginning of the Tertiary layer, was a thin layer of red clay, about 2 to 2.5 centimetres in depth.
When Walter showed samples of this red clay to his father, physicist and inventor Professor Luis Alvarez of the University of California, Berkeley, the latter had the samples analyzed. They were found to contain the chemical element iridium, but in concentrations many times greater than that contained in the surrounding limestone – iridium being one of the rarest elements to be found in the Earth’s crust. This led them to suggest that this iridium was present as the result of the collision of a huge asteroid with the Earth. Asteroids are bodies composed of rock, varying enormously in size, which orbit the Sun. Large numbers are found between the orbits of Mars and Jupiter, though some have more eccentric orbits.7 Asteroids which originate from this so-called asteroid belt are rich in iridium.
The impact would have generated a massive fireball in which the asteroid would have been vaporized into a gas cloud, which would have reached high into the Earth’s atmosphere. The theory is that this would have obscured the Sun, causing the temperature of the Earth to fall drastically. Some indication of the magnitude of the event is indicated by the discovery, at more than 100 locations worldwide, of similarly high concentrations of iridium in clay deposits laid down at the time of the K-T Boundary.8
The search for an asteroid crater, of the size demanded by such a colossal event and created at the relevant time, was now on.
The ‘Chicxulub’ Crater
A possible candidate was discovered in 1978 by geophysicist Glen Penfield, an employee of the Oil Company of Mexico, in that country’s Yucutan Peninsula. The so called Chicxulub Crater (named after a nearby village) was 110-miles or so wide, and partially submerged beneath the ocean. The outcome was that, in September 1991, a scientific paper entitled ‘Chicxulub Crater; a Possible Cretaceous/Tertiary Boundary Impact Crater on the Yucatan Peninsula, Mexico’ was published in the journal Geology, by authors Alan Hildebrand, Penfield, and others. Having given their reasons for believing that the crater had indeed been created by the impact of a meteorite (defined as ‘a meteor that survives its passage through the Earth’s atmosphere such that part of it strikes the ground’, they concluded that ‘The age of the crater is not precisely known, but a K-T Boundary age is indicated’.9
There appeared to be a flaw in this argument, however. In March 2004 Swiss-born US palaeontologist Gerta Keller (Professor of Geosciences at Princeton University, New Jersey, USA) and others published in the Proceedings of the Academy of Sciences of the United States of America an article entitled, ‘Chicxulub Impact predates the KT Boundary Mass Extinction’. In it they declared that the aforementioned impact predated the K-T extinction by about 300,000 years.10 This, however, was not the end of the story.
The ‘Shiva’ Crater
Mexico’s Chicxulub Crater is dwarfed by the Shiva Crater, approximately 500 kilometres in diameter, which lies largely submerged off the coast of India, west of present-day Mumbai. It was discovered in 2009 by paleontologist Professor Sankar Chatteηee of the Museum of Texas Tech University, Texas, USA, and Dhiraj Kumar Rudra of the Geological Studies Unit, Indian Statistical Institute, Kolkala, India.11 It was given the name, Shiva, after the Hindu god of destruction and renewal. But the unanswered question is, was this crater caused by meteoric impact, and if so, did the impact occur at the time of the K-T extinction?
Deccan volcanism
Another candidate for causing the Earth to cool was volcanic activity in the region of India’s central Deccan Plateau which, according to Professor Gerta Keller and others, ‘can now be positively linked to the K-T mass extinction’.12
Other factors
It may be that the Earth’s cooling was unrelated to the activity of meteorites or volcanoes. For example, an alteration in the trajectory of the planet’s elliptical orbit, which took it farther away from the Sun, might theoretically, produce the same effect.
Were the dinosaurs asphyxiated by poisonous gas?
Could it be that the alleged asteroid collision caused the planet to be enveloped in poisonous, life-extinguishing gases? If so, then why were mammals, birds, and reptiles not annihilated also?
Could the dinosaurs have starved to death?
Was it that the dinosaurs simply ran out of food, perhaps when Earth become covered in ash, following the alleged asteroid impact? This is an unlikely scenario, given the diversity of dinosaur species on the one hand, and the diversity of vegetation on the various continents, on the other. And again, if this was the case, how was it that other species survived?
* * *
Of these various theories, the likeliest one is that dinosaurs became extinct because, during one or more periods of global cooling, they were unable to maintain their body temperatures on account of heat leaching out from their poorly insulated skins. But is this the end of the story?
NOTES
1. Oxford Dictionaries Online.
2. Ibid.
3. Eagle, et al., ‘Dinosaur Body Temperatures Determined from Isotopic (13C-18O) Ordering in Fossil Biominerals’, Science, 23 June 2011.
4. Oxford Dictionaries Online.
5. Brattstrom, ‘Body Temperatures of Reptiles’, American Midland Naturalist. 1965. 73 (2): pp.376–422.
6. Price, Gregory D. and Elizabeth V Nunn, Valanginian Isotope Variation in Glendonites and Belemonites from Arctic Svalvard: Transient Glacial Temperatures during the Cretaceous Greenhouse’, Geology 2010: 38. pp.251–4.
7. Oxford Dictionaries Online.
8. Alvarez, Alvarez, Asaro and Michel, ‘Extraterrestrial Cause for the Cretaceous-Tertiary Extinction: Experiment and Theory’, Science 208, 1980 (4448): 1095–1108.
9. Hildebrand, Penfield, Kring, Pilkington, Camargo, Jacobsen and Boynton, ‘Chicxulub Crater; a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico’, September 1991. Geology 19 (9), pp.867–71.
10. Keller, Gerta, et al., 2004, ‘Multiple impacts at the KT boundary and the death of the dinosaurs. Impact predates the K-T Boundary Mass Extinction’, published in the Proceedings of the Academy of Sciences of the United States of America, 16 March 2004, Volume 101, Number 11, pp.3753–8.
11. Chatterjee, S. 1997, ‘Multiple Impacts at the KT Boundary and the Death of the Dinosaurs’, Proceedings of the 30th International Geological Congress 26: 31–54.<
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12. Keller, Sahni and Bajpai, ‘Deccan Volcanism, the KT Mass Extinction and Dinosaurs’, Journal of Bioscience, 34(5), November 2009.
Chapter 33
Birds: The Only Surviving Dinosaurs
On 24 October 1867 Darwin’s friend and colleague Thomas H. Huxley was examining, in Oxford University’s Museum, the fossilized ilium (large broad bone forming the upper part of each half of the pelvis)1 of a dinosaur. This, he observed, was avian-like. Furthermore, when the British Museum’s specimen of an Iguanadon was reconstructed as a biped (rather than a quadruped), this led Huxley to remark that there was ‘a considerable touch of a bird about the pelvis & legs’. The following year, at the Royal Institution, Huxley explained that the Ratites (a group of mainly large, flightless birds, such as the ostrich) were the descendants of Compsognathus-like dinosaurs.2 (Compsognathus – a genus of small, bipedal, carnivorous theropod dinosaur.3)
In other words, dinosaurs did not entirely become extinct, since at least one species survived, from which modern-day birds are descended.
Archaeopteryx
It was German palaeontologist Christian E. Hermann von Meyer who first discovered a fossilized feather belonging to this creature in 1860 at Solnhofen, Germany. The following year, when the first complete specimen was unearthed from the Solnhofen Plattenkalk (or Solnhofen limestone) Jurassic beds of Bavaria, he gave it the name Archaeopteryx lithographica (lithographic being the type of fine-grained, yellowish limestone in which the fossil was discovered). The fossil was sold to London’s Natural History Museum where, as already mentioned, it was examined by Professor Owen. Several more such specimens were subsequently discovered in the same beds.
Archaeopteryx lived in the Late Jurassic period, 150 million to 145 million years ago; its name deriving from the Greek words archaīos, meaning ‘ancient’, and ptéryx, meaning ‘feather’ or ‘wing’. Because of the exquisite preservation of the fossils, it has been shown that the skeleton of archaeopteryx is basically that of a small theropod dinosaur (a carnivorous dinosaur of a group whose members are typically bipedal and range from small and delicately built to very large).4 However, attached to each arm was a feathered wing, and the body and tail were also feathered. At the end of each wing and foot were three separate fingers, each tipped with a curved claw.
Archaeopterix was, of course, long extinct by the time of the K-T Boundary and therefore it cannot be considered to be a direct ancestor of modern-day birds. However, it is considered to represent a transitional stage in the evolution of the theropod dinosaur to the biological class of vertebrates, Aves, that comprises the birds.
Since Archaeopterix, many more examples of feathered dinosaurs have been discovered. For example, in September 2009 an article entitled, ‘Fossils Provide “Missing Link” between Dinosaur and Bird’ by Richard Alleyne, Science Correspondent, was published by The Telegraph (online).
Newly discovered fossils of a four-winged dinosaur have been hailed as the ‘missing link’ that finally proves [that] the prehistoric creatures evolved into birds. And five fossils recently unearthed in China show an eagle-sized Jurassic dinosaur that has feathers on its arms, legs, feet and tail. Paleontologists believe that the limbs would have developed into wings and enabled the tiny predators to take to the skies.
The new feathered species were found in two separate rock formations in north east China – the tiaojishan, which would put the fossils at 168 million to 151 million years old, and the daohugou formation, which would make them 164 million to 158 million years old.
The dinosaurs in question were Troodontids, a predominantly small-bodied group of feathered theropods. One of them, which was given the name Anchiornis Huxleyi (Anchiornis – from the Greek anchi, meaning ‘near to’; ornis – ‘a bird’, and Huxleyi – after Thomas Henry Huxley – Darwin’s ‘Bulldog’), was the size of a chicken, and had ‘extensive plumage and profusely feathered feet’. Said Professor Xing Xu of the Institute of Vertebrate Palaeontology and Palaeoanthropology at the Chinese Academy of Sciences, Beijing, China,
This fossil provides confirmation that the bird-dinosaur hypothesis is correct and supports the idea that birds descended from theropod dinosaurs, the group of predatory dinosaurs that include allosaurus and velociraptor.5
The dinosaur/bird precursor
The missing links between theropod dinosaurs and modern-day birds remain largely to be discovered. However, it is interesting to speculate as to what the dinosaur precursor of birds may have looked like, and to ask how did it survive the dinosaur extinction?
The dinosaur/bird which was extant at the time of the K-T Boundary extinction, and survived this catastrophic event, is likely to have been a relatively small creature, in which case its food requirements would have been equally so. It is also likely that it was compact in shape, with no excessively elongated extremities to make it vulnerable to heat loss.
Why did the ‘bird-dinosaurs’, alone of all the species of dinosaur, survive?
If it is the case that bird-dinosaurs were endothermic, and obliged, like modern-day birds, to maintain their body temperature at a comparatively high optimum level of between 40 to 42 degrees Centigrade – which was several degrees above that required for the remaining, non-avian dinosaur species – then the fact of their survival is remarkable. Furthermore, the fact that modern-day birds possess a heart and circulatory system, strongly implies that their fellow dinosaurs of the Cretaceous era were similarly endowed, making them even more susceptible to heat loss from the body. Why, therefore, did they not succumb to the alleged ‘cold event’ which allegedly occurred at around the time of the K-T Boundary?
The answer is that fully evolved feathers and down (fluffy plumage) act in the same way as hair and fur in preventing heat being lost from the body – i.e. by retarding movement of air across the surface of the skin and by trapping pockets of air within themselves. (In fact, feathers and down are made of exactly the same material as hair and fur – i.e. keratin). Furthermore, birds (like mammals) are able to increase the insulating capacity of their skins by ‘puffing themselves up’ – i.e. deliberately causing their fur or feathers to stand on end, thus increasing the depth of the insulating layer.
NOTES
1. Oxford Dictionaries Online.
2. Huxley to Phillips, 31 December 1867, Oxford University Museum, 29, and Matthew and Harrison, Oxford Dictionary of National Biography.
3. Oxford Dictionaries Online.
4. Ibid.
5. ‘Fossils Provide “Missing Link” between Dinosaur and Bird’, by Richard Alleyne, Science Correspondent, 25 September 2009. The Telegraph (online).
Chapter 34
The Eugenics Debate
‘Eugenics’, a term coined by Darwin’s half-cousin Francis Galton, is defined as the science of improving a population by controlled breeding to increase the occurrence of desirable heritable characteristics.1 Although many ‘eugenicists’ claimed to have been inspired by the work of Darwin, including Galton himself, the actual word only came into being after Darwin’s death. On a more sinister note, some have blamed Darwin for producing ideas which set off a chain reaction, culminating in one of the greatest crimes against humanity in the history of the world – namely the Nazi Holocaust of the twentieth century. To what extent this is true will be discussed shortly.
Thomas Malthus
In 1798, in An Essay on the Principle of Population, Malthus declared that, by human intervention, ‘The capacity of improvement in plants and animals, to a certain degree, no person can possibly doubt’. In other words, by means of selective cultivation from ‘a wild plant’, a ‘beautiful garden flower may be produced’, and similarly, by selective breeding, the most ‘desirable qualities’ of cattle or sheep. Therefore
It does not … by any means seem impossible that by an attention to breed[ing], a certain degree of improvement, similar to that among animals, might take place among men.2
The real perfectibility of man may be illustrated … by the perfectibility
of plants. The object of the enterprising florist is, as I conceive, is to unite size, symmetry, and beauty of colour.3
[However] As the human race … could not be improved in this way, without condemning all the bad specimens to celibacy, it is not probable that an attention to breed should ever become general …4
Malthus can therefore claim to be one of the very first eugenicists. He foresaw, however, that difficulties and dangers might befall those who attempted to apply the practice of eugenics to human beings, for
an experiment with the human race is not like an experiment upon inanimate objects. The bursting of a flower may be a trifle. Another will soon succeed it. But the bursting of the bonds of society is such a separation of parts as cannot take place without giving the most acute pain to thousands: and a long time may elapse, and much misery may be endured, before the wound grows up [heals] again.5
Erasmus Darwin
Darwin’s grandfather Erasmus, felt that it was important for a person contemplating marriage, to recognize in a potential spouse, the presence of inheritable diseases.
As many families become gradually extinct by hereditary diseases, as by scrofula, consumption, epilepsy, mania, it is often hazardous to marry an heiress, as she is not infrequently the last of a deceased family [i.e. the remainder having succumbed to hereditary disease].6
(In fact, the first two diseases which Erasmus mentions above are of an infectious, rather than of a hereditary nature.)