The theory of evolution underpins the life sciences, but also impacts many areas of the physical sciences. It really is a foundational concept to much of modern science. We'll cover the basics.

Introductory video


The five sections on this site cover:

  • An introduction to molecular (DNA) and morphological (anatomy) evolution – Section 1.
  • Variation – sources and its heritable nature – Section 2.
  • Competition, and fitness in the context of evolution – Section 3.
  • Natural selection – Section 4.
  • Speciation, and evolutionary (phylogenetic) trees – Section 5

Do bear in mind that evolution is a vast topic: this website scratches the surface. If you find it interesting, the remaining sites on Evolution and Palaeobiology build upon it.

1 – Molecular and morphological evolution

Evolution impacts on both DNA (molecular evolution), and – especially in multicellular organisms – anatomy (morphological evolution). In this video we meet some basic underlying principles, and then look at how these two forms of evolution are linked.


  • There are three fundamental properties of a system that are required for evolution to occur, namely:
    • Variation.
    • Heredity.
    • Selection.
  • In multicellular organisms:
    • Selection acts on organisms, and results in changes to genomes across generations.
    • The genome dictates the phenotype through the process of development.

2 – Sources and heritable nature of variation

Evolution would not be possible without variation that can be passed down between generations. Let's dig a little deeper.


  • The source of variation is mutation. Most mutations are bad for the organism that has them (they are called deleterious mutations).
  • Uneven survival only drives changes across generations because variation can be inherited.

A thought experiment

Given what we've covered so far, have a think about the following.

You have ~infinite time, and your own pack of wolves (!?) How would you go about creating a pack of chihuahuas?


Timber wolves

Timber wolves. Photo by Martin Cathrae (CCBY).


Couldn't find a source for this. Sorry!

Have a think, and when you are done, scroll down past the aristocratic whippets below to learn more about the origin of dogs!

Misse and Turlu, Two Greyhounds Belonging to Louis XV – Jean-Batiste Oudry

Misse and Turlu, Two Greyhounds Belonging to Louis XV – Jean-Batiste Oudry

The answer?

When you have had a chance to think about this, expand the item below for some background regarding the domestication of dogs – which is pretty much what we're looking at, even though I didn't explicitly use the word domestication!

Whence dogs?

The key process at play here is something called artificial selection, a process humans facilitate through selective breeding. Here is a definition for you:

The practice of selecting animals for breeding on the basis of phenotypic characteristics such as their appearance, performance, or production records. This is common in breeding dogs (Caninae) for showing, horses (Equidae) for racing, and farm animals for milk or meat production. Source

Using this process allows humans to control phenotypic development. To domesticate dogs, you might chose to select for:

  • Tameness (i.e. breed those individuals which are least afraid of humans)
  • Smaller size
  • Other physical traits such as smaller jaws, diminished craniofacial development

Here is what we actually know of this:

  • The genetic divergence between dogs and wolves began between 40,000–20,000 years ago
  • There are competing theories to how domestication may have occurred
    • Humans may have captured wolf pups for use in guarding or hunting, resulting in selection for traits of importance for these new roles
    • Alternatively, as humans changed from a nomadic to sedentary lifestyle during the dawn of the agricultural revolution, wolves may themselves have been attracted to dumps near early human settlements to scavenge
  • This is quite an active area of research, and new ideas are coming out all the time. (And of course, some of this assumes you believe Chihuahuas are tame – I understand some people believe they're not that chill).
Bonus info: Domestication syndrome

More broadly, looking at domesticated animals, we can identify a suite of behavioural, physiological, and morphological traits that are associated with domestication. This is referred to as domestication syndrome.

It includes (but is not limited to) docility and tameness, changes in coat colour, reduced tooth size, changes in craniofacial morphology, and alterations in the form of ears and tails form. In addition to these morphological traits, it is also associated with changes to the reproductive cycles and hormones of the animals, shifts in the concentration of a number of neurotransmitters, a longer period of juvenile behavior, and reductions in total brain size, and also of specific brain regions.

Recent research suggests that these may all be linked, and current work is exploring the mechanisms that might underlie this – these could, for example, be developmental.

If you want to read more, this paper is a good place to start: Wilkins, A.S., Wrangham, R.W. and Fitch, W.T., 2014. The “domestication syndrome” in mammals: a unified explanation based on neural crest cell behavior and genetics. Genetics, 197(3), pp.795-808.

So there you have it – now you know a bit more about the origins of dogs... Including Misse and Turlu.

3 – Competition, and fitness

In order to understand natural selection, we must first meet a key concept that underpins this – fitness.


  • In its simplest form, fitness is relative lifetime reproductive success.
  • There are many different factors that, together, ultimately dictate the fitness of an organism.

4 – Natural selection

Now we have fitness down, let's look at a core process in evolution: natural selection.


  • The fitter organisms produce more offspring; over time the frequency of fitter organisms in a population increases. This is natural selection.
  • Responses to selections are seen in the form of adaptations.
  • Selective pressure is the a factor that impacts on the reproductive success of an organism.
  • Behaviour can cause changes beyond simple competition for resources – an example is sexual selection.

5 – Speciation, and evolutionary trees

Evolution occurs on a multitude of scales - in space and time. Let's look at a few considerations/concepts above the level of the individual in evolution.


  • An important concept in the evolution of eukaryotes is the species. This is the lowest in a hierarchical nesting of divisions we can use to categorise life.
  • A species can be defined in a number of ways: one is whether a group of organisms is reproductively isolated or not.
  • Evolutionary trees (phylogenies) can be used to show the relationships between and within groups of organisms.

Let's finish with a quiz

We've now covered the basic of evolution. Let's put it into practice. With a quiz! Below you can see something cool – an ant (left), and a spider (right). What's going on?

An ant in and an ant-mimicking spider in Gorongosa National Park, Mozambique

An ant and an ant-mimicking spider in Gorongosa National Park, Mozambique. Photos by Thomas Shahan.

In its simplest terms, they look alike – and the fact they do is a result of evolution. What we are seeing here is a form of mimicry (this form is actually Batesian mimicry if you're interested). The spiders resemble ants in great detail - both in terms of their morphology (see the narrow "waist", for example), and in terms of behaviour – they wave anterior appendages to look like antennae and walk in a distinctive zig-zag way. In spiders such as this, research suggests that the selective pressure driving this mimicry is the fact that predators such as spider wasps and other, larger, jumping spiders, avoid ants. Cool, huh? Our quiz is going to be about the selective pressure that may be driving a series of adaptations in some multicellular organisms!

In case you're wondering just how deep this spider-ant rabbit hole goes, there is evidence that appearing like an ant can also help these spiders prey on others which are ant averse, some of these spiders mimic different ant species at different points in their development from juvenile to adult, and some resemble one ant carrying another, worker, ant (though just the boys do this in the species in question):

Male Myrmarachne plataleoides from Thailand.

A male Myrmarachne plataleoides from Thailand (Sean Hoyland).

Isn't that just amazingly cool?