SURFACE AREA TO VOLUME RATIO:

from: http://a1604.g.akamai.net/7/1604/940/20000516/images.egreetings.com/e-products/m_main/cgi/../card_jpg/epgi1631.gif

As temperature increases, we can increase our surface area (S.A.) by stretching out which increases heat loss. Body volume, however, stays the same. As a result the total S.A. to Volume ratio increases. Humans use a similar behavioral mechanism as the cat shown above. During winter, if a person is cold they are likely to have a hunched appearance with arms held close to the body. As a result, surface area is decreased and we retain heat better.