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Evolution is like a fly in tube, limited in where it can go but not how quickly it can get there
The Museum’s Professor Anjali Goswami has led her team to developing a model that indicates how we can expect evolution to occur. The findings will be published by the journal Evolution and available online from today.
Evolution is not a random process but one limited by developmental constraints. Professor Goswami explains, 'Very early on in a group's history there are lots of possible directions for evolution, and there is usually a burst of diversification. But as animals continue to develop, limitations arrive and groups are locked into pathways of evolution which dictates how things can and can't evolve.' Prof Goswami argues that rather than there being one optimum way for a predatory mammal to evolve, for example, there are relatively few ways that it can evolve dependent on its species’ developmental programme.
To simulate this model the team used surface and CT scanners to create 3D models of 350 bird skulls from eight international collections, including the Museum’s Collection housed at Tring. Postdoctoral researcher Ryan Felice explains how ‘Computationally-intensive analyses were employed to identify subtle-to-huge changes across the bird skulls, like the way the very tip of the snout has changed over time, allowing us to clearly see which parts are variable and which are less so.'
After mapping different parts of the model skulls, and examining how each part was constrained or facilitated in its evolution, the team found that different parts of a skull can evolve at different rates. For example, parts of the bird skull that have a tight constraint on it – such as the point at which the skull and neck joins together – evolve slowly and with little variation in shape. Whereas the beak seems to be less constrained to an evolutionary pathway and is observed to create new shapes more often.
The study also found that the parts of the skull that are evolving fastest tend to be made of specific types of tissue. Anything made of older, ancestral tissue types evolves more slowly, and bones made up of a mix of tissues evolves the fastest, suggesting that diversity in developmental origin creates diversity in form.
Highlighting the importance of this study, Professor Goswami says ‘With such a large dataset, we can use these findings to make certain predictions about how evolution might occur in birds and other vertebrates. We can also now understand why some forms are common, evolving over and over again in different groups, while other forms that we can imagine have never evolved at all.’
For this research, the team used a new approach to capture the complexity of the skull in far more detail than previously attempted, and will continue to use this approach to study skull evolution across all vertebrates, from salamanders to dinosaurs, using a dataset of several thousand 3D scans.
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