Speciation theory assumes that evolutionary change accumulates over space and time. However,

the role of hybridization in speciation remains a matter of debate. While widely accepted as an

important evolutionary force in plants, its role in animal diversification has been deemphasized as

‘volutionary dead end’until recently. With the dawn of next generation sequencing techniques to

decode genomes, however, evidence accumulates that hybridization between closely-related

species may act as a ‘ega mutation’in animals too - and as such - boost speciation when new trait

combinations become advantageous in novel environments. Introgressive hybridization, the process

whereby genetic material from one lineage becomes fixed in another, has been identified as a key

evolutionary driver in Darwin finches and Victoria Lake cichlids. Yet, its role in adaptation within the

wake of human disturbances remains poorly known, despite the important theoretical and applied

implications thereof. To bridge this knowledge gap, we here study a bird species-complex that is

known for its fast pace of evolution across large parts of the world, in a well-studied ecological

model system in East Africa. By integrating genomic analyses with environmental niche modeling

and phenotypic measurements, we assess the extent at which introgressive hybridization affects

speciation in relation to ecological processes, and which genotype-phenotype and genotypeenvironment

associations may act as main drivers.