Skip to main content

Directional, stabilising and disruptive natural selection


Natural selection leaves a certain gene pool’s allele make-up quite different depending on selection pressures. The results are quite easy to understand. Take a population of toads. Directional selection would happen if smaller toads avoided predators better, hence larger toads would be gobbled up more frequently. The average toad size in the following generations would shift in the DIRECTION of the smaller extreme.


Stabilising selection, on the other hand, shifts extremes towards the middle values. Say small toads have less reproductive success, and large toads are more appealing to predators. Average-sized toads will be best adapted to that situation (of course, unless they too happen to have some “issue”, in which case, bad news for the toad empire). 


Finally, perhaps the most bizarre of these is disruptive selection. It occurs as a result of extreme phenotypes (noticeable traits) being better adapted to the environment than mid-range values. Say smaller toads survive better due to weather conditions during a certain period of time, while larger toads survive better during other times, but average-sized toads have no advantage at any given time.


This stuff becomes so much more interesting when applied to humans. Where you live, which type of selection do you think is taking place?

…if any.

Comments

Post a Comment

Comment...

Popular posts from this blog

4 Reasons Google's Calico Won't "Solve Death"

The on-line world has been taken ablaze by Calico's bid to end ageing, and thus death itself, but is this what they will actually focus on, and will they achieve it? The fact is ageing will be reversed, and death by "natural causes" will go with it. The questions are "When?" and "By whom?". Until recently, not a lot was known about the approach Calico would take in this venture dubbed "moonshot thinking" - a term touted by Google as the source of all considerable human progress throughout history. This we don't doubt, but is this what Calico is all about? CNN's Dan Primack has revealed details about Calico's plan , which hint at a less-than-moonshot thinking approach, and cast a serious question mark on its ability to deliver the punchy TIME headline. Here is why: 1. The man with the idea, Bill Maris, arrived at the conclusion that the root of all death-causing disease is simply ageing itself. Not only is this widely ...
11 comments
Read more

Principles of Evolution - Sexual Selection

If it weren't for sexual selection, evolution itself would be a passive process. Natural selection isn't sufficient in the evolution of life, because it does not deal with predictions of future selection pressures. For example, if a massive natural disaster were to wipe out every single collared pigeon on Earth, then there would be no process in place to bring the collared pigeon back to life. Since the development of the pigeon from its ancestor must have taken a very long period of time, it is a really inefficient idea to just let the pigeon's fate hang by chance. Admittedly, if all members of that species were to be wiped out, the chances of it being reintroduced would be very close to zero. So, how does sexual selection work to avoid such fates of death of a species? Firstly, let's establish that sexual selection is not the process of reproduction, or self-propagation, but the process by which certain properties are chosen over others to deal with potential future...
3 comments
Read more

Alien Life

Alien life, what an exciting topic! Let's investigate some principles of life which might help illuminate what life forms there are on other planets. One of these principles states that "not all life that can exist does, but all life that cannot exist does not". What this means is that, just because we have discovered certain chemical and physical environments that suggest a life form (for example an earth worm), doesn't mean that an earth worm exists there, or that it will ever exist. However, if the environmental properties are analysed accurately, then it is possible to make an assumption that it is likely for a certain life form to have existed there, or for it to be likely to sometime develop there. The reason why "all life that cannot exist does not" is fairly obvious, either because life will not develop in unfavourable conditions, or because life in unfavourable conditions dies. Another result of that principle is that evolution never reaches a dea...
2 comments
Read more