Positive sexual selection is the most important and obvious type. It is positive because it involves the promotion and support of a characteristic, be it good looks or ambition, sense of humour or colour. Positive sexual selection is the driving force that results in variety of organisms, as well as the variety of what those organisms make, for example chocolate corn flakes or oats and fruit. This type of sexual selection is found in so many things, a popular example of which is teenage behaviour when teenagers feel the urge to pick things to support, be it a music genre, a sexual orientation, a fashion, a sport, or a club. Positive sexual selection is what fan clubs are made of.
Know when you see something on facebook and you MUST LIKE it? You absolutely must click like? The drive behind that urge is positive sexual selection. You like that and everyone must know. Not because you want them to like you, but because you want them to like that thing. This urge might seem superficial, but in fact it is very primal.
With positive sexual selection, comes negative sexual selection. I suppose this is easy to guess. Negative sexual selection can be exampled by hate groups, protests, and all the rants about how disgusting Marmite is. A very popular form of negative sexual selection is found in politics and religion. You're on a forum, and someone has said something you disagree with. You get a really hot unstoppable urge to argue with them; you don't even know them, but it doesn't matter because you think what they said is so unacceptable it must be challenged. Studies have shown that in fact negative sexual selection is stronger than positive sexual selection. For example, saying "STOP WAR" has more impact than saying "KEEP PEACE". This may be explained by the potential danger of not acting when faced when something threatening. That is, people see it more dangerous if the wrong party gets the vote, than beneficial if the right one does.
Neutral sexual selection is just that, neutral. Nothing good or bad will happen as a result of it. You don't care about your partner being taller or shorter than you because you don't see a benefit or downside to either. Shopping at ASDA or Sainsbury's makes no difference to you, and you don't think it makes a difference to anything else. Maybe even the parties make no difference to you, so voting is pointless.
And finally, why does Facebook not have a dislike button? As mentioned above, negative s.s. is stronger than positive s.s., so in the event of facebook adopting a dislike button, people would get more bothered about topics, posts and comments, which would spur arguments and hard feelings between members, potentially making the facebook experience worse, and leading to real life events facebook may be sued for. Imagine "Boy hangs himself after tens classmates "dislike" photo". To keep things light and... positive, facebook ensures that positive sexual selection (which people generally find enjoyable) dominates the experience, through the like button.
Check back next time for a new topic on alien life, Alien Life II, in which we're going to look at some of the evolutionary principles that sci-fi films such as Resident Evil and the Alien series have used in order to create their characters/monsters.