Wind chill Re: Guide for anti-AATers

Bill Burnett (bbur@wpo.nerc.ac.uk)
Fri, 10 Nov 1995 15:02:25

(Phillip Bigelow) writes:

> I am not sure this is true. Wet fur actually behaves like a wet suit on a
>SCUBA diver; it provides a layer of body-warmed water between the diver and
>the surrounding water. It's along the same principle as a double pane of
>glass on a window.
> Likewise, when the SCUBA diver comes out of the water, he *still* feels
>warm, because of the insulating nature of the trapped water in his suit.
>The same principle seems to be at work with the polar bear. The
>water-soaked fur acts like an insulating wet-suit when the bear is in the
>water, and as an insulation from the hypothermic affects of wind-chill when
>the bear is out of the water. Fur is actually a *benefit* for aquatic
>mammals,because it allows the animal to dry off SLOWLY, and thus avoid the
>the unpleasant wind-chill effects of being "blasted" dry by the air.

No, I think you are wrong here. There is no benefit in drying
off 'slowly', nor is the 'insulating layer of water' effective once you're out
of the water. On the contrary, the less water you retain on exit the better,
as the evaporating water will rob you of body heat in the same way as sweat
does. In my experience a wet wet suit is a very chilly thing to be in out of
the water. Even thin lycra jumpsuits worn in the tropics for protection from
various stinging beasties can hold enough water to chill you considerably...
It's actually warmer to take the thing off so your skin dries faster
especially if it's at all windy. Come to Scotland and watch the divers
desparately stripping in the lochside car parks some time... Well, the stupid
ones without drysuits anyway (he said smugly...)

The thing to remember with wetsuits is that the layer of warm water inside the
suit represents a loss of body heat (you had to warm it somehow.) Unlike air,
water is a very good conductor of heat, so wetsuits do not function like
double glazing at all. What provides the insulation in a wet suit is 3-7mm of
foam neoprene, the less water inside the better, so you want a tight fit which
firstly reduces the thickness of the water layer and secondly reduces flushing.

The fur of (most?) marine mammals is very dense and oily. Ideally
this fur is almost waterproof and the water does not reach the skin. In such
cases the fur acts like a drysuit rather than a wetsuit, trapping a layer of
air against the skin, not water. This has the advantages of using the
excellent insulative properties of air plus reduced chilling on exit as the
evaporating water is not in contact with the skin. I believe sea otters have
the thickest pelts of all. If you watch one diving you can see a 'silvery'
coating which is the trapped air, and they leave a trail of tiny bubbles. Sea
otters spend hours grooming every day to make sure their fur is in peak
condition, otherwise if it becomes matted it's insulating properties are
severely reduced. Less effective fur functions by reducing the rate of water
flow over the skin.

AAT proponents might well argue that no hair or fur is better than ineffective
hair or fur in a semi-aquatic setting, and they might well be right about that
provided the AA gets out of the water regularly. I would argue that unless
the AA spent rather a lot of time out of the water, or jumped in and out a
lot (to avoid the crocs??? :-)), then it would be better off keeping it's
hair, in fact shortening and thickening it. Now if the AA is spending a lot
of time out of the water, the mooted advantage of bipedalism must come from
elsewhere, mustn't it?

I agree wholeheartedly that the AA is in serious trouble from heat loss, it's
the wrong shape and size and it's supposed to be spending a lot of time in the
water. Without doing any calculations I speculate that it would be a pretty
knife edge existence gathering enough food to 1) cover basic metabolic needs
2) compensate for heat loss 3) have sufficient excess to lay down thick layers
of fat or hair 4) provide nutrition for young whose problems will be
aggravated by small body size and inability to gather food for themselves for
a considerable length of time. Any speculative aquatic 'Lucy' would solve all
her problems by getting OUT OF THE WATER. Climb a tree, eat fruit. Forage on
the shore at low tide. Even catch fish in rock pools. But at all costs stay
dry. So why be bipedal?

Bill