RE: Temperatures on Earth
November 27, 2014 at 7:09 pm
(This post was last modified: November 27, 2014 at 7:40 pm by Anomalocaris.)
(November 27, 2014 at 5:25 pm)lifesagift Wrote: Plane and simple really... it's our normal body temperature that determines the conditions in which we operate best.
So that's begs another question.... why 37.2 deg C?
Wouldn't blood run quicker at 53.4 deg C, so making oxygen distribution much quicker, and hence humans much fitter, faster etc?
It's much more complicated. Most metabolic function involve some form of protein reaction. Different protein reactions occurs best at different temperatures. As a result, organisms adapted to different metabolic temperatures uses a different suite of proteins to support their metabolic functions. Even the same metabolic function often uses a different protein in a cold adapted organism than in a hot adapted organism.
The proteins an organism can synthesize and uses are deeply encoded into its genes. For highly complex organisms like mammals many proteins are required to support life. One could not easily change out some proteins and leave others in place without throughly disrupting life critical functions. So once the protein suite, and their coding genes, of a family of highly complex organisms become adapted to a certain metabolic temperature, the hurdle to changing that temperature is very high. A whole suite of genetic changes must all occur more or less at once to successfully change the metabolic temperature of members of that family without killing it.
This is why most placental mammals, including humans, have almost the same metabolic temperatures. Once the first ancester of placental mammals perfected a suite of genes and proteins suited for metabolism at 37C, it became very difficult for any of its descendants to adopt a different metabolic temperature without compromising some life critical function. Birds as a group, whose ancesters probably evolved endothermic independently of mammals, also have mostly similar metabolic temperature of around 40C.
As to why the first ancester to adopt 37C Metobolic temperature adapted that particular temperature and not any of the other possibilities, the specific details of answer is probably hard to determine from about 100 million years later. But we can be fairly certain the general outline of an answer would be something like:
1. There is benefit to maintaining a steady metabolic temperature. This enables an animal metablize efficiently all the time and to remain active and alert when it is cold as when it is hot. So this gives the animal the ability to outcompete another which becomes lethargic when it gets cold due tout diminished metabolic rate and efficiency.
2. But There is a high energy cost to high metablic temperature. A placental mammal with a fixed body temperature of 37c must eat 10 times more calories than a cold blooded reptile of similar size to keep up the body temperature. So an animal would not tend to evolve metablic temperatures higher than necessary to gain from 1.
So the first placental ancester to evolve 37C metablic temperature probably found that temperature to be the best attainable compromise between 1 and 2 in its living environment. Once it's genes and metablism settled into 37C, it became difficult for its descendant to change it. Consequently virtually all subsequent placental mammals kept the 37C metabolic temperature even though their have diversified from the arctic to the tropics.