• Question: Why does evolution occur?

    Asked by lolz to Adam, Emily, Thad, Thomas on 12 Mar 2015.
    • Photo: Thomas Clements

      Thomas Clements answered on 12 Mar 2015:

      This is a good question and often people answer with the famous phrase from Darwin: ‘Survival of the fittest’.

      This doesn’t mean which animal can run or swim the furthest but which animal fits in the best to it’s environment.

      Lets take an example to illustrate the point.

      There is a type of moth which is green and blends in to the tree trunks it lives on really well. When it creates a new generation (i.e. has babies) all the green ones survive and go on to have more baby moths. Also in this generation there are a few moths who are born with black wings, so they don’t blend in very well and they are eaten by birds.

      Suddenly, down the road a factory that burns coal is built by humans. The smoke blows through the forest covering the trees in back soot. Suddenly the birds can see all the green moths and start to eat them. But the black ones are now camouflaged and so they can mate much more and lay eggs, meaning that future populations are much more likely to have black wings. Over time this happens over and over again until all the moths in the forest are black because they survive better.

      This is evolution in progress. It sounds far fetched but this has actually been seen occur in the wild and is a really famous example of evolution!

      This is a very simple example but evolution can be broken down in 5 main laws. Check them out and learn about evolution here:
      http://necsi.edu/projects/evolution/evolution/5parts/evolution_5parts.html

    • Photo: Thaddeus Aid

      Thaddeus Aid answered on 12 Mar 2015:

      Hi,

      When DNA copies itself it never does it perfectly, there are always new mutations being added to the population. So in each new generation there are a ton of new mutations all fighting for a place in the population, almost all of these mutations are what we call “neutral”, which means they don’t do anything. But occasionally, a mutation that is helpful enters the population and the individual that has it has a leg up on everyone else and will be more likely to live and have babies, who in turn will be better at surviving and having babies, etc.

      So take for example humans. We all come from Eastern Africa (near Ethiopia) about 70,000 years ago and each baby born since then has added between 75-150 new mutations into the human population. Nearly all of these are neutral and most of them have disappeared, but occasionally something useful appears like the ability to drink milk as an adult. Now this is only useful if you have domestic animals to get milk from and other food sources are scare for part of the year.

      Did you know it is a mutation that some adults can drink milk without farting? There is a sugar in milk called Lactose, babies have a special enzyme in their stomach that breaks lactose in half which allows it to be digested. All mammals are like this, babies drink their mother’s milk when they are born, however since mammals stop drinking milk after being babies the body shuts off the enzyme and the mammal can no longer digest lactose. This causes the lactose to be passed into the rest of the digestive track (the intestines) where bacteria eat the lactose and give off gas as a response giving the adult smelly farts.

      But in Europe, one person 15,000 years ago or so mutated so that they continued to produce the enzyme as an adult and could digest lactose. This gave them an additional source of food during the winter which helped them to survive the cold winters of Europe before there were Tescos to buy food at. So from this one person now 95% of Northern and Western Europe all have this mutation. Pretty crazy, right? Everyone in Europe that can drink milk as an adult is descended from this one person!

      Going into the future other features that help humans will continue to spread through the population just like the ability to drink milk did. I personally think that most of our future evolution will revolve around fighting diseases.

      I hope that answers your question!

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