Have you ever wondered why we are what we are? Perhaps you have thought about all the different species of animals that exist and wondered where they came from? Or maybe you have wondered why some organisms become extinct while some are completely thriving?

Well, during your studies in Biology this year, you will hopefully come up with answers to all these questions. You will venture into the fascinating topic of evolution and understand how different organisms came to be.  

This article will give you a brief overview about what’s to come.

But first – what comes to your mind when you think of evolution? In general terms, evolution means to gradually develop. Some simple examples would be a plant growing from a seed, or a caterpillar developing into a butterfly.

However, the definition of evolution is slightly different when we think of it in terms of biology. Rather than thinking about the growth of an individual organism, we are interested in understanding how different living organisms have developed from earlier ones, during the history of the world.  

Let’s delve into this concept more deeply.

Natural Selection

We can’t talk about Evolution without bringing up the great Charles Darwin. He’s the one that proposed the Theory of Evolution by Natural Selection.  

He described evolution as ‘descent with modification,’ which means that species change over time and give rise to new ones. This was supported by his theory on Natural Selection. The best way to describe this concept is with an example.

Let’s say that we have a population of ladybirds, some are red, and some are blue. These insects live in a habitat that has a lot of red flowers. Birds are the ladybird’s main predators, and since the red ladybirds camouflage into the red flowers, the blue ones are more likely to be eaten by the birds. Therefore, since the red ladybirds are better suited to their environment, they are more likely to survive, and thus, pass their genes onto their offspring. As a result, overtime, the fraction of blue ladybirds living in the area decreases.

It really is about the survival of the fittest.  

These are the four main processes that Natural Selection relies on:

  •      Overproduction of offspring
  •     Variation
  •      Selection
  •      Reproduction of Adaptations

Factors that Drive Evolution

Evolution is not a process that just happens, there’s reasons why it occurs.

An organism’s genetic fitness refers to their ability to survive in their environment long enough reproduce and pass their genes onto the future generation.

A selection pressure is an environmental factor that can influence an organism’s genetic fitness. Thus, the presence or absence of certain selection pressures is what drives evolution.

 There are two categories that selection pressures can fall into.

Biotic – selection pressures that are dependent on other organisms.

  •       Diseases
  •       Predators
  •       Food availability
  •       Pollutants

Abiotic – selection pressures that are related to non-living factors.

  •       Temperature
  •       Sunlight
  •       Water Availability

What type of selection pressure do you think drove the process of natural selection in the example given above?

When you think about selection pressures, it is important that you consider the age of the individual. For example, if there is a factor that only affects older individuals, that are unlikely to reproduce, it doesn’t contribute to their genetic fitness. They’ve likely already passed their genes onto a new generation!

Evidence for Evolution

You might be wondering – is there any proof that evidence has occurred? For all we know, all organisms on earth now may have looked the exact same 100000 years ago!

Well, there’s concrete evidence that tells us that evolution has occurred over the years.

Here’s some pieces of evidence that you need to know about:

The Fossil Record

The fossil record is a documentation of fossils that have been found over time. By comparing fossils to the structure of the organisms that we see nowadays, we can see how creatures have changed over time. It also tells us how different species are related to each other.  

We can tell how old a fossil is by considering how deep underground it was found.

Everything we know about dinosaurs is from the fossil record!

Comparative Embryology

This involves comparing the similarities and differences between the embryos of certain species. By looking at all the stages of embryo development, scientists can better understand how two species are related.

Molecular Homology

This is a method that is used to compare the relatedness of organisms that live nowadays – doing this still helps us get valid information about evolution!

In molecular homology, scientists compare the macromolecules (such as DNA and proteins) that are found in organisms. The tracked macromolecules are usually ones that are extremely important to the organism’s function, such as haemoglobin.

Species Distribution

This refers to the geographical area that a species can be found. The areas that certain species can be found depend on evolution, and the selection pressures that characterised the environment.

For example, Australia is home to a lot of marsupials, but in other parts of the world, mammals are mostly placental. Since Australia is an island, these marsupials were able to evolve without competition from mammals in other parts of the world.

Hopefully you found this article about evolution interesting and will continue to enjoy this topic as you learn it in class! If you need a hand with some definitions for this topic, you can access a free glossary here.