So, Rob has already covered the fact that evolution happens at a number of scales. This lecture focusses on the larger scales that he mentioned. This video give a quick overview of what we'll be covering (and highlights a slight change of approach for this lecture – that I'd love your feedback on).

Introductory video


We're going to cover:

  • Adaptation – Section 6.1.
  • Macroevolution:
    • Concepts & Clocks – Section 6.2.
    • Rates – Section 6.3.
    • Adaptive radiations – Section 6.4.
    • Zoom - (Palaeo)EvoDevo

As I mentioned in this video, you'll find a slight shift to how I'm delivering the content this time around. I would love your feedback. You can find a feedback form at the bottom of this page.

6.1 – Adaptation

Evolution is driven my 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.

Associated task

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.

6.2 – 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. Or just drop me an email if you'd like me to go over it in our Zoom session.

6.3 – Rates!

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

6.4 – 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 ancetstral 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.

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.


I outlined in the introductory video, that this time I've changed slightly how I am delivering the course content, with the last video being delivered through, and the basis of, discussion on zoom. Shorter asynchronous elements at the expense of discussion time face to face. Any feedback you have would be very much appreciated (it's all anonymous too, FYI).

Many thanks for your thoughts.