EVO-DEVO: Evolution meets Development

Evo-devo (a.k.a. evolution & development) is a fascinating field of biology that aims to explain the evolution of living beings, by analyzing the differences in their embryonic development.

Vertebrate embryos — courtesy of Encyclopædia Britannica.

It doesn’t matter whether it’s a plant or an animal, the forming of a complex organism always requires a well-executed plan: specific genes must be turned on in particular tissues, at the right time and in a certain amount. It turns out that the genes that regulate the development of complex organisms have been conserved throughout evolution.

The development of all organisms requires that specific genes are turned on in particular regions of the body, at the right time and in the right quantities. Homeotic genes, here expressed in a fruit fly and mouse embryos, are highly conserved genes that orchestrate the development of the body plan of many animals. Image courtesy of macmillanhighered.com

According to evo-devo, it’s the different temporal, spatial and quantitative expression of these genes that allows natural selection to work. This means that developmental genes are able to produce different body shapes and plans, depending on how they’re used in time and space, and depending on how much intensely they’re turned on. If, by chance, a new particular body shape arises, evolution will promote it if it increases the fitness (a.k.a. ability to retrieve food, escape from predators, reproduce etc.) of a species. This could explain the biodiversity we observe today. In the images you can see some examples.

Salamanders have different fingers according to their lifestyle. At the top (courtesy of iNaturalist) you can see a salamander capable of climbing trees, thanks to shorter and curved fingers. Below (courtesy of Wikipedia), you can see a salamander with longer fingers, which are excellent to walk on the ground.

Some salamanders are able to climb trees because their fingers are shorter and stocky: this is achieved by reducing the expression time of the genes that are responsible for the development of the limbs (heterochrony)- the shorter the time, the shorter the fingers.

The cellular proliferation of the sepals allows winter cherries to have a broad inflorescence. Image adapted from Portale del Verde.

Winter cherries have a distinct broad inflorescence, which is achieved by expressing in their sepals genes which are typically only used in leaves to promote cell proliferation (heterotopy).

Abyssal fishes do not need eyes to see as there’s no light. Image adapted from ExtremeTech.

Some abyssal fishes live in deep underwater caves, where there’s no light and eyes are of no use: their absence is achieved by overexpressing the genes which, at lower rates of expression, normally split into two domains the eye field in other fishes (heterometry).

These are only a few simple examples. By studying the differential expression of developmental genes, evo-devo aims at explaining the history of living beings, shedding light on the major evolutionary nodes of complex organisms.