Why do dogs like jumping into cold ponds, while cats and humans generally do not?
鈥� Your questioner appears to be confusing willingness with enjoyment. Most dogs are prepared to dive into cold water, but they may not like the experience. And in referring to cats, your questioner is almost certainly referring to the domesticated species, which is not necessarily representative of its genus.
Nonetheless, the canine tolerance for cold water, and feline intolerance, lie in their respective evolutionary histories. The dog (Canis lupus familiaris) originated in central Asia during the aftermath of the last ice age, at least 15,000 years ago. It is descended from the grey wolf (Canis lupus), with all the evolutionary baggage that implies. Ice-age wolves preyed on sub-Arctic herd animals such as elk, reindeer and caribou, which would have migrated in search of better grazing, crossing fast-flowing rivers swollen by meltwater when required.
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Any animal 鈥� including the ice-age wolves 鈥� fording or swimming these rivers would have had to develop considerable physical and psychological resistance to low temperatures. Those that weren鈥檛 prepared to get their feet wet wouldn鈥檛 have lasted long enough to pass on their genes. Those that did bequeathed their doggy descendants a tolerance for cold water.
鈥淲olves that wouldn鈥檛 get their feet wet wouldn鈥檛 have lasted long enough to pass on their genes鈥�
Some 5000 years after the big bad wolf began the transition to being man鈥檚 best friend, a group of wild cats (Felis sylvestris) in what is now western Asia apparently attached themselves to the local human population in a semi-symbiotic relationship. Significantly, the closest living relative of the proto-kitties is believed to be the (Felis margarita), a denizen of regions of extreme heat and aridity, such as the Sahara.
This ancestry was never likely to cultivate a hereditary tolerance for getting wet, even if natural selection had not already instilled a wariness of bodies of water, whatever their temperature. Large mammals have no freshwater predators in the sub-Arctic, but animals originating in the tropics have good reasons for not going into the water, most of them possessing very powerful jaws. A prehistoric African water hole was a fast-food outlet for large predators, both in and around the water.
The behavioural heritage of these widely differing ancestries can be most clearly observed when our modern-day pets are drinking. A dog will generally lap up its water enthusiastically, albeit with the occasional sideways glance at any animal that could attack. A cat, on the other hand, displays far more caution, constantly looking around suspiciously and keeping its body as far back as possible from the liquid.
Hadrian Jeffs, Norwich, Norfolk, UK
鈥� Dogs, like humans and cats, exhibit a homeothermic mode of temperature regulation 鈥� their body temperature remains constant in spite of fluctuations in the temperature of their environment.
Dogs are covered with thick hair to conserve internal heat, and regulate their body temperature through panting, an extremely efficient method. On a hot day it is quite common to see a dog with its mouth wide open and tongue hanging out.
鈥淒ogs regulate their body temperature through panting, an extremely efficient method鈥�
Recent research has also indicated the presence of a complex network of blood vessels in the basal part of a dog鈥檚 neck. This region functions as an efficient temperature regulator. In addition, dogs have relatively large spleens. When a dog is active or under stress, the spleen contracts and releases blood into the circulatory system, which provides yet another mechanism for carrying excess heat to the skin.
All this means that dogs are better adapted than humans or cats to withstand cold shocks or hypothermia.
Saikat Basu, Lethbridge, Canada