Evolutionary biology

For Darwin, comparative embryology was important evidence in support of the evolution of descendants from a common ancestor. In 1874, the German biologist Ernst Haeckel followed Darwin’s line of thinking with the notion that ancestral developmental processes are repeated during embryonic development, and are a record of evolutionary ancestry … ‘Ontogeny (development) recapitulates phylogeny (evolutionary history)’ …  the biogenetic law that dominated evolutionary thinking in the late 19th century.  

Often misinterpreted as referring to the recapitulation of adult forms rather than the forms of embryos, Walter Garstang at Leeds University, highlighted the problems of recapitulation theory in 1921, by pointing out that an adult cannot evolve directly into another adult. According to Garstang, embryonic development represents the stages of ancestors to whatever point it was in ontogeny when divergence into new forms occurred. In effect ‘Ontogeny does not recapitulate phylogeny – it drives it’. He realised that the larval stages of adult forms of many animal taxa were, according to Henson (personal communication) precociously hatched embryos. Subject to Darwinian selection, larvae are potentially the nodes for major evolutionary innovation as the result of selection of larval characteristics consequently affecting adult morphology/physiology in subsequent generations.  

Developmental changes that might be the node (starting point) for the evolution of new taxa (descendants different from their ancestors in the sense of new species or higher taxa . . . family, order, class) depend on the:
* position of embryonic presumptive tissues within the developing embryo
* gradients of transcription factors which affect the development of embryonic tissues
* sequence of switching on and off the genes that control development
* timing of gene switching.

These factors are almost certainly not the whole picture but perhaps prompt a re-definition of evolution as:
. . .  a change in the interaction, timing, order and degree of expression of the genes which control developmental processes, or more concisely as:
. . .  a modification of ontogeny (development) as the result of Darwinian synthesis, developed during changes in gene regulation (where/when/how much gene product) and not necessarily as:
. . . a change in gene frequency . . . a central idea in the Neo the 1920s/’30s, and dominant in evolutionary thinking to the 1980s.

Today, investigating the gene interactions controlling development and how these have changed thro ugh time resulting in the evolution of new taxa is now possible using the techniques of molecular genetics. Arkhat Abzhanov at Imperial College, UK et al have unravelled with colleagues the intricacies of the genetic interactions controlling beak development in Darwin’s finches, deepening our understanding of how new finch species/sub-species have evolved from a common ancestor arriving on the islands from South America about two million years ago.

Evolutionary developmental biology (evo-devo) highlights how the interactions between genes might affect the micro evolution (see … Galapagos Tales) and macro evolution of lineages (see … Larval Forms). Today, the emerging discipline reframes the arguments of earlier evolutionary thinking, adding molecular biology to our understanding of how developmental processes influence evolution. The sessions explore a synthesis of these ideas to reassess the nature of evolution in process.

Learning outcomes

The learning outcomes for this course are:

• An ability to integrate the abundant evidence from work in developmental biology and molecular genetics that increases understanding of the processes of micro- and macro-evolution;  
• An appreciation of how the discovery and understanding of DNA have contributed to current evolutionary thinking;  
• An understanding that phylogenetically the genetic regulation of development is highly conserved, constraining the basic body plan of metazoa to a set of components in common (not “… endless forms …”) see Charles Darwin, On the Origin of Species. 

Classes

1. Evolution through Natural Selection: the growth of an idea is the theme that runs through the week’s sessions on Evolutionary Biology. The session begins with a review of evolutionary thinking before Darwin and subsequently.  

2. Development and evolution … beginning in the 19th century, we explore the growth of the idea that embryology and development are important evidences that underpin the evolution of evolutionary theory from Darwinism to the current paradigm of the Integrated Synthesis.  

3. The title Larval Forms identifies the topics of the session’s content. We explore in detail the idea that types of larvae are in effect precociously hatched embryos that ancestrally were nodes of evolution of taxa morphologically very different from the adult stages of the juvenile forms of the life cycles described in the session.

4. Initially the history of Darwin’s finches and their influence on evolutionary theory is discussed in this session entitled Galapagos Tales. Then we take a detailed look at the long-term ecological studies that are informing current ideas about the processes that lead to speciation in the birds that are icons of evolution in action but were an enigma to Charles Darwin.  

5. Entitled The Tales continue … the session covers the developmental origins and molecular genetics of speciation with particular reference to Darwin’s finches. The session finishes with concluding remarks referring to simple field work investigating speciation in a meadowland plant community local to Cambridge compared with what has been learnt about speciation in Darwin’s finches. Finally, we think of Charles Darwin as an undergraduate at Cambridge walking the meadows with his friend and mentor John Stevens Henslow, seemingly unaware of the evidence for speciation at his feet. 

Required reading

Watson, J D (2017) DNA: the story of the genetic revolution. Alfred A. Knopf, New York  

Hardy, A  (1956)  The Open Sea: Part 1 The World of Plankton. Collins, London  

Brakefield, P M (2011) Evo-devo and accounting for Darwin’s endless forms. Phil. Trans. R Soc B; 2069-2075  

Grant P R, Grant B R (2014) 40 years of Evolution: Darwin’s Finches on Daphne Major Island. Princeton University Press, New Jersey  

It would also be to the advantage of students to view the following video resources on YouTube before the sessions indicated. Viewing after each session will help to consolidate the content of each session’s powerpoints. Each video can be accessed by searching YouTube using the titles as listed.  

Session 3: Larval Forms  

> What is a veliger? CollinLabPanama
> Bipinnarias George von Dassow
> Feeding appendicularians (Oikopleura spp.) DTU Aqua Broadcast
> Understanding the behaviour of microscopic marine larvae - University of Plymouth  

Session 4: Galapagos Tales  

> Galapagos Finch evolution HHMI Biointeractive video
> The Evolution of Darwin’s Finches on the Galapagos Islands - Harvard Museum of Natural History 

Typical week: Monday to Friday

For each week of study you select a morning (Am) and an afternoon (Pm) course, each course has five sessions, one each day Monday to Friday. The maximum class size is 25 students. Your weekly courses are complemented by a series of two daily plenary lectures, exploring new ideas in a wide range of disciplines. To add to the learning experience, we are also planning additional evening talks and events.

Evaluation and Academic Credit 

If you are seeking to enhance your own study experience, or earn academic credit from your Cambridge Summer Programme studies at your home institution, you can submit written work for assessment for one or more of your courses. 

Essay questions are set and assessed against the University of Cambridge standard by your Course Director, a list of essay questions can be found in the Course Materials. Essays are submitted two weeks after the end of each course, so those studying for multiple weeks need to plan their time accordingly. There is an evaluation fee of £65 per essay.

For more information about writing essays see Evaluation and Academic Credit.

Certificate of attendance

A certificate of attendance will be sent to you electronically within a week of your courses finishing.