Wool and Woolens Wool denotes soft, curly fleece fibers from domesticated sheep. It differs fromhair in that its scales are more numerous, smaller, and pointy. Curliness makes wool very resilient. This high tensile strength and elasticity help wool fabrics to retain their shape. These properties, wool's lightness, and its fine insulating ability make wool fabrics desirable. Wild sheep have sparse, woolly undercoats and coarse hair, useless in fabrics. The hair has been bred out in domestic breeds. Sheep fleeces are usually shorn annually, from late spring to early summer. The wool is cut off very close to the skin and removed in one piece, weighing nine to eleven pounds.Wool from different fleece parts varies in its fiber length, fineness, and structure. The shoulder and sides yield the best fibers. Merino sheep yield the best overall wool. It makes up 40 percent of all wool produced commercially. Crossbreeds of merino sheep and strains that produce longer, coarser wool yield most of the rest. Some apparel wool comes from alpacas, goats, and llamas. Woolen cloth manufacture begins by pulling fleeces apart and choosing the best fibers for given uses. Next, fibers are cleaned to remove lanolin and dried-on sweat. The clean fibers are disentangled and drawn straight by carding, which entails passing them between rotating cylinders to yield a thin film or web. Web processing varies, depending on whether it will be used in tweed or worsted yarn. Tweeds, woven from bulky yarn made of short, randomly arranged fibers, are thick and fuzzy.Worsted fabrics such as gabardines are woven from web made of longer, thinner fibers, tightly twisted for smoothness.
Adaptation to Environment Natural selection leading to a new species may be accelerated when members of the original species move to a new environment, whether voluntarily or driven by the elements. Separated populations may develop different traits as they adapt to their new condition. Eventually, they will become sufficiently different to be unable to produce offspring with members of their original population. This process has repeated itself many times, over millions of years, and accounts for the large diversity in the animal world, not to mention the additional diversity consequent on artificial breeding by humans, widely observed among domesticated animals such as horses, cattle, and dogs. Animals occupied new environments as species living in water moved to the land or later to the air. Thus, the step from fish to amphibian was essentially one from living in water for the whole life to living on land for the adult stage of the life cycle. The step from amphibian to reptile was one of increasingly proficient adaptation to land life at all stages of the life cycle. Birds and mammals evolved in different directions from the reptiles, the first in adaptation to an arboreal and finally a flying life and the second as a further advance in the maintenance of an even and high body temperature-homeothermy-by combining an insulating external layer such as hair with a variety of physiological thermostats. Events in geology, climate, and flora also determined the geographic distribution of species. Thus, marsupials are currently found almost entirely in Australasia and South America. The tiger exists only in India and Southeast Asia. The lion is restricted mainly to Africa. This pattern reflects the way in which these groups have evolved in relation to the physical world. Newanimal groups evolve into many different forms, especially when they become dominant. For instance, when mammals came to occupy the dominant position, some became meat-eaters while others became vegetarians; some became smaller while others became larger; some became runners while others ended up as burrowers or flyers; still others returned to the water. This trend allowed the descendants of the original type to exploit a much greater range of environments and resources. Essentially, those species whose sense organs or brain morphology and functions improved the most ended up being dominant- primates in general and humans in particular.
