A scientifically imperfect but easy to understand definition is that evolution is the changing of the gene set of a species over generations. It’s evident that this change is inherent to every species where the progeny is not an exact copy of it’s progenitor. A child does not have the exact same DNA set as either of his/her parents, thus s/he is “the next step in evolution”. This can be a bit misleading since the word “evolution” sounds like it’s development, advancement, but it not necessarily is in the biological sense. It simply means change.
A little “side note”… The whole argument of evolution vs. creation is meaningless because of two things:
- Evolution exists and it’s a fact. Even if we are god’s creation, evolution is in a sense just another word for “change” and thus it can not not exist.
- Evolution is not an explanation of how life came to be. Evolution presumes that life already exists. Material without life can’t “evolve” itself to live. So the theory of evolution is not an “opponent” of the theory of creation – the two are dealing with entirely different things.
The thing which made sure that evolution meant improvement in the biological sense is natural selection. The difference between these two can be understood if we realize that we as an advanced civilization “stopped” natural selection but not evolution. Our DNA set as a species is changing by the minute, only now it’s not necessarily improving (see Idiocracy) – but I digress.
Natural selection means two things: those who can’t adapt to the dangers of their surroundings (predators, etc.) die with more probability before leaving progeny behind, and those who have more progeny reaching the age of their fertility will have a better chance at their sets of DNA surviving in the long run. The survival of the fittest and the “prolification of the busiest”, respectively.
It’s very easy to make thought experiments with natural selection. Start with a wide range of features and properties and most of the times it’s easy to realize who survives and who doesn’t.
Example 1: There is a human population with 500 men and 500 women. The DNA of the men vary a lot. Some like sex a lot while others are not interested. Those who doesn’t want to have sex most probably won’t have children and so will have their genes removed from the common gene pool immediately or within 1 or 2 generations at most. Those who are obsessed with sex will have more children and thus their DNA has a better chance of surviving. Conclusion: we are all the descendants of people who liked f*cking very much.
Example 2: Same premises. The age of women these imaginary men desire varies from 1 to 100. Those who desire women too young or too old to bear children will obviously have their genes removed from the pool. Conclusion: we are all the descendants of men who desired the most fertile women. We have it in our DNA to desire those women who exhibit signs of fertility even if we don’t recognise these things consciously.
The long-term effects of millions of years of natural selection are ingrained into us. It’s not something conscious; it “hides” in our desires and instincts. Those can’t be changed by social pressure. They can only be suppressed with more or less success but this “going against our very nature” almost always results in emotional stress and of course it will often result in dying without offspring, ie. an evolutionary dead end. Yes, instincts might change slowly over many generations as our environment and social norms change, but a handful of human generations cannot change what is “set in stone” by millions of years of natural selection. (The Stone Age lasted for 2.5 million years and is roughly the 99% of human history.)
By now it should be evident that knowledge about evolution and natural selection might be used to understand the instincts and desires of us humans. This knowledge can be vital today when birth rates are dropping and more and more people die without children. If you want to have children – or if you just want to have sex – this knowledge can give you a decisive advantage over others.