Age of Animals

Quaternary Period, 2.588 MYA - present

During this period four Ice Ages, separated by warmer interglacial periods, covered the northern land areas. As the ice slowly advanced and retreated, the climate zones and their mammal faunas moved across the continents via the Bering region and Panama Isthmus. An unexplained feature of this period was the appearance of giant representatives of nearly every order of mammals, from platypus, kangaroo and lemur, to deer, beaver, edentate and unusually large elephant. However between 40,000 and 5,000 years ago many of the world's largest mammals died out as shown in Figure 17a. Most of them weight 90 lbs or more. The smaller animals such as mice and shrews almost all survived. Irrespective to the cause of extinction (there are many speculations such as climate change and slaughtered by humans),

Figure 17a Quaternary Period Extinction [view large image]

large animals have the disadvantages that its smaller size of population is more vulnerable and they have a much slower rate of reproduction taking years to give birth.

Close examination of their genome shows that it was riddled with deletions and an abundance of stop codons (for stopping mRNA transcription). In particular, the mutated genes are related to smell, urinary proteins, and translucent fur (Figure 17b,b). The meltdown was caused by small population, which permits bad mutations to rack up, since there was no competition. Such observation is very important for the preservation of modern species on the brink of extinction.

Figure 17b Death of the Woolly Mammoths [view large image]

(see a BBC documentary on "Woolly Mammoth Died Out", also see the 2017 article on "Dying woolly Mammoths" in Nature).

• There existed two major hominid species about half million years ago - the Homo sapiens neanderthals in Europe and the Levant (see Figure 18), and the Homo sapiens sapiens (see Figure 19) in Africa. The most significant feature of Neanderthal anatomy is the skull. The typical features include a wide, vaulted cranium, heavy 'beetle brow' ridges above the eyes, a big jaw, and large teeth. An adult male is thought to have been around 5'6". Neanderthals may have looked faintly apelike, but their brain capacity was as large as, and in some cases larger than, that of modern human beings. As a whole, Neanderthals seem to have been tough and stocky individuals. The difference

  		in mitochondrial DNA between Neanderthals and modern humans is 25-30 nucleotides, while it is only 8-9 nucleotides in modern individuals. Anatomically Modern humans (AMH), who emigrated from Africa about 65000 years ago, may have slaughtered the Neanderthals. Eventually, around 35000 years ago only one species, Homo sapiens sapiens, was left. We thus find ourselves alone and yet the most numerous and successful primates in history. Such success may be at the expense of the natural environment. All the giant animals disappeared around this time. Since this was not associated with any obvious climatic change, we must therefore suspect that human may very possibly have played a large part in these extinctions2. The earth's mammal faunas have been even more reduced during the last hundred years, until many of the herbivores that once roamed North America and Africa in their thousands are nearly extinct or can be seen only in protected game parks.
  Figure 18 Neanderthals [view large image]	Figure 19 Homo Sapiens [view large image]

		geological past. However, it has been argued that the present rate of extinction is sufficient to create a major mass extinction in less than 100 years. Others dispute this and suggest that the present rate of extinctions could be sustained for many thousands of years before the loss of biodiversity matches the more than 20% losses seen in past global extinction events. Figure 21 is an artist's impression of an idyllic scenery at the dawn of civilization.
Figure 20 Diversity of species [view large image]	Figure 21 Idyllic Scenery before the Mad Rush [view large image]

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