There have been some experiments done where if you put fruit flies in a different environment they will adapt/evolve accordingly to survive in that environment. Almost every species evolves to adapt best according to its environment, right? All I'm wondering, is whether those changes are random, or a result of adaptation to their environment.
Here is a very important point to see whether beneficial mutations are random ors non-random: Make an experiment, take a population of beings, split up the population randomly and then put these isolated groups into areas with the same changed environment.
The expectation is that all of these groups adapt to the changed environment after some time. If you expect that mutations that will cause this change are random, you will expect that different groups will evolve different strategies to deal with the changed environment. If you expect that such mutations are non-random but somehow caused by the environment, you would expect that all of the different groups evolve the same strategy to deal with the changed environment.
A few months ago I read about such an experiment on some bacteria, I think. In that experiment, they could show that different populations evolved different strategies although they were faced with the same environment.
I'm not suggesting that adaptation is intelligent by any means, it can be the result of blind repitition. If a lizard has to repeatedly feed on leaves, it gradually adapts by evolving a digestive system to digest the vegetarian diet, if apes have to walk on open grasslands rather than swing on trees, they adapt by eventually becoming bipolar, etc.. Hardly intelligent but a result of change in environments.
That's how it works. But all the changes are based on random mutation. If you think otherwise, you would have to propose a mechanism by which something you do can influence your genetic code in a way so that your offspring can do it easier. Something would be highly unlikely because the genetic code is quite complex and not a simple plan of your body.
But I think, that if suddenly humans were forced to live inside a tunnel where they had to walk on all fours to get around, eventually, over a long period, their bone structure & genes would change so their offspring would be better suited for walking on all 4s than standing upright, it would result in less backpain as it would do for a present day human being, etc. This would be the result of adaptation imo.
Another possibility is that humans would just be smaller. Because the smaller you are the less problems you have living in a place with a low ceiling, the less likely you are to have more offspring.
People already come in different sizes, so it is easy to imagine how humans would become smaller and smaller because always the smallest ones be the ones with best survival chances.
If a random mutation caused a baby to be born / produced such that its skeleton structure was better suited to walk on all 4s than upright, even in a minor but noticeable way, the experiment would be disproved.
But that is very much likely the case. You forget that you would not be able to easily spot such a situation. When looking around, people's bones do have very small differences. Such differences would be the first step towards evolving towards walking on all fours. You know, there are a lot of people that get problems with their back very early in their lives. I am sadly one of them. Have had back-pain since I was 25. In a world where everyone walks on all fours, it could be that I was better off. I (and people that suffer the same problems) could be the first step towards evolving towards walking on all fours, if such a situation would ever arise.
Topic: Some questions about evolution