The great escape: do parasites break Dollo's law?

Area of Science:

• Evolutionary biology
• Developmental biology
• Parasitology

Background:

• Dollo's law posits that complex traits, once simplified, are unlikely to re-evolve.
• This principle has historically suggested a unidirectional evolutionary path from complex to simple states, especially in parasitism.
• The law implies a qualitative distinction between simple and complex traits, rather than a quantitative one.

Purpose of the Study:

• To challenge the long-held assumption of irreversibility in evolutionary character loss.
• To re-evaluate Dollo's law in the context of evolutionary developmental biology.
• To explore the potential for regaining complex traits from simplified states, particularly in parasitic organisms.

Main Methods:

• Review of recent evolutionary studies on trait regain.
• Analysis of developmental pathways and genetic mechanisms underlying trait simplification and complexification.
• Comparative studies across different taxa, including parasitic lineages.

Main Results:

• Evidence suggests that complex structures can indeed be re-evolved from simpler states.
• The distinction between simple and complex traits is likely quantitative, not qualitative.
• The 'one-way trip' paradigm in parasitology may be an oversimplification.

Conclusions:

• Dollo's law may not be a universal principle, and evolutionary reversibility is more common than previously assumed.
• Complex traits can be regained, challenging the notion of irreversible evolutionary simplification.
• This has significant implications for understanding parasite evolution and adaptation.