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

First Blog, Ever.

Before we start to explore evolution, let me outline what this blog is about, and what approaches it will take. Most people are aware of the theory of evolution. However, the predominant context of it has been restricted to the animal kingdom, and the most obvious animal of all has been ommitted: you, the human. Us, Homo sapiens. Articles of so-called "evolutionary psychology" may jump up in your head right now. Something about the colours women wear, or the jobs men want. Something about sex, something about money. Something silly. This blog aims to explore the fundamental principles of life and evolution, and apply them to the surrounding world, with an emphasis on humans. This blog aims to challenge evolutionary psychology with evolutionary biology. This blog aims to cast light on many dark areas such as: What is the cause, course and effect of life? Are there principles which apply to all forms of life, on Earth and other places in the Universe? Can we predict life fo...
4 comments
Read more

The "Purpose" of the Female Orgasm

I read on Wikipedia today that the female orgasm has no reproductive use, whereas the male orgasm does. Who the hell comes up with this bollo**s? Firstly, orgasms by themselves cannot be directly related to reproduction, since the vast, vast, vast majority of living things reproduce just fine without them. Secondly, there is no such thing as purpose in evolution. Our idea of purpose is something preconceived to serve a function. For example, a chair is made to be sat on. A typewriter is made to be typed with. A blog post is written to be read and shared. Evolution does not work that way. Nothing is ever made to serve any function because nothing is made according to a function, before that function exists. The concept of function itself is tightly dependent on the environment. A function is the relationship between two things which are connected to each other by cause, effect and time. The only reason most things have a function in living things is because those that did...
5 comments
Read more