Evolution happens at a number of scales, from small shifts in population, to the rise and fall of phyla. This lecture focusses on the larger scale patterns.


We're going to cover:

  • Adaptation – Section 1.
  • Macroevolution:
    • Concepts & Clocks – Section 2.
    • Rates – Section 3.
    • Adaptive radiations – Section 4.
    • (Palaeo)EvoDevo; Section 5.

Understanding evolution on these scales is fundamentally fascinating – or at least, I find it so. But it is also really important if we want to see how, for example, life and the planet Earth have interacted over the past several billion years. Evolution, on a large scale, dictates so much about the nature of the world around us, that it's harder to find somewhere where it has no impact, than where it does!

1 – Adaptation

Evolution is driven by adaptation. We've not really covered it in this course yet, so here seems like a great place to start!


  • An adaptation is a trait that:
    • Can be passed between generations.
    • Helps an organism survive and reproduce in its environment.
  • Adaptation is the process by which organisms become adapted.
  • A common process in the evolution of complex traits is exaptation: the change in function of a trait.

Something to think about

Is adaptedness the same thing as fitness? I think this is a really interesting question.

No need to spend more than a couple of minutes thinking about this. I'll put some thoughts at the bottom of this page.

2 – Concepts and clocks

The main topic of this lecture is macroevolution. What is this? Well in order to dig into that, I wanted to quickly get us on the same page with a couple of terms I'll be using a lot. These are:

  • Interspecific: existing or occurring between different species.
  • Intraspecific: existing or occurring within a species or between individuals of a single species.

I will try and pronounce each of these very clearly as they sound kind of similar!


  • Macroevolution is probably best defined a evolution that occurs through sorting of interspecific variation.
  • This is a useful concept assuming processes (e.g. fitness, competition and selection) differ within and between species.
  • The red queen hypothesis emphasises biotic processes, over abiotic ones (=the court jester), as drivers in evolution.
  • By calibrating the rate of molecular evolution with fossil ages, we can estimate clade divergence times, and thus evolutionary rates.

Note: The version of this video where I explained molecular clocks more fully ran on far too long. But, fear not, if you want to learn more, I've put a link in the bonus stuff section to an article I wrote that explains it in a (hopefully) understandable way.

3 – Rates!

Cool cool cool. So we can estimate rates. But what can these tell us? Let's find out!


  • Using molecular and morphological clocks we can investigate rates of evolution.
  • For example, these suggest that the Cambrian explosion may have been a short period of elevated rates of evolution.
  • The idea that evolution is gradual and consistent (phyletic gradualism) held sway for a long time.
  • An alternative – that evolution happens in bursts with stasis in between (punctuated equilibrium) – is quite hard to test.
  • It seems likely that different environments lend themselves to different variation in rates.

4 – Adaptive radiations

Much of the biodiversity in modern ecosystems is thought to stem from things called adaptive radiations. Let's learn about these, then think about how they, and rates, might interact.


  • An adaptive radiation is an event in which a lineage rapidly diversifies from an ancestral one
  • The newly formed lineages evolve different adaptations.
  • Rates of evolutionary are thought to be elevated at the start of these events in many instances.

5 – (Palaeo) Evo Devo

Lets finish by looking how the development of an organism – its ontogeny – can help us understand its evolutionary history. And what we can tell of development in the fossil record.


  • Some elements of ontogeny – especially the genetics of development – can shed light on evolutionary history. Examples include:
    • Showing the homology between different segments of the arthropod head
    • Clarifying the origins of insect wings
  • There is evidence of the ontogeny of complex organisms preserved in the fossil record, but in places this can be challenging to interpret.

Bonus stuff!

Well done, you've reached the end of this website on macroevolution. I hope you have enjoyed learning about it as much as I enjoyed writing it! Here is some bonus material that I hope is also interesting.

In which Russell does his best to explain molecular clocks

As I mentioned above, I didn't the time to explain clocks in the detail I would ideally like – there's too much exciting science to cover, and not enough time. But I have written an explanation of how Bayesian approaches to phylogeny work, in their basic form, that you can find here:

Garwood, R.J. 2020. Patterns in Palaeontology — Deducing the tree of life. Palaeontology [online] 8(12):1-10.

If you want to know more about how they work in terms of clocks, then give me a shout, and I will happily explain!

Is adaptedness the same as fitness?

I asked you above, whether you thought that being highly adapted (showing high levels of adaptedness) was the same as fitness. I think this is a really interesting question (hence me asking).

In brief, within a given environment an adaptation – to that environment – does make an organism fitter. But being highly adapted does not always mean you will have a higher fitness. For example, think about the example I have used previously of the avocado with its giant seed. This adapted to being distributed by a megafauna that is now extinct. While being highly adapted, because that fauna has now gone extinct, the avocado is no longer particularly fit – there is nothing out there left to spread its seeds. This is one example of how these two things can become decoupled.