A short article on another factor that we humans take for granted, but we never had the luxury of, when we were running barefoot in the fields hunting large mammals. Don not get hot under your collar man I'm talking about temperature control (it would not be a article without a bad joke). Today, we live in a world where ambient temperature is constant. Rather than tougher the environment we have air conditioned, or heated, buildings, cars and public transport and so on. It is not often we have to face the extremes in temperature unless we are running from the taxi to the building door. We are typically in a very narrow temperature range that suits us. BUT, and there is always a but, this comes at a cost.
There is an ambient thermoneutral zone where energy expenditure is minimized to maintain internal temperature in our bodies. When the temperature is too cold, we expend energy by shivering to try and heat ourselves up. If it is too hot we sweat to cool ourselves down. If it is within this zone then our bodies do not need to spend so much energy to maintain core body temperature (37 deg cel). With modern technologies we are lucky enough to keep ourselves within this zone almost all the time. The byproduct is that our bodies spend far less energy to stay warm than they would have done otherwise. This technique is commonly used to promote weight gain in livestock and I see no reason why it would not occur in us too.
In the year 2000 I was lucky enough to travel to Antarctic continent to do some researches, field work and study fish and penguin populations down there. I was very cold most of the time and I put on 10 kilograms because I was constantly eating. This is a very common phenomenon when people go to the 'ice'. They eat and eat and eat and put on a lot of extra weight. The amount of energy needed to keep warm is huge and typically a person eats double the amount of calories they normally do to keep up. Of course I had free supply of food and made the most of this food. The message from this is that our bodies can spend a HUGE amount of energy keeping warm or cool, and this energy is no longer used in today's world.