Here's why:
* Shared Ancestry: Both hedgehogs and echidnas belong to the mammal class, but they diverged from a common ancestor millions of years ago.
* Different Evolutionary Paths: Over time, they evolved along different evolutionary paths, adapting to different environments and ecological niches. This led to significant differences in their physical characteristics, behavior, and physiology.
* Convergent Features: Despite their divergent evolution, both hedgehogs and echidnas have developed spines as a defensive mechanism. This is an example of convergent evolution, where unrelated species develop similar traits due to similar environmental pressures.
Key Differences:
* Geography: Hedgehogs are found in Europe, Asia, and Africa, while echidnas are native to Australia and New Guinea.
* Reproductive System: Hedgehogs are placental mammals, while echidnas are monotremes, laying eggs.
* Diet: Hedgehogs are primarily insectivores, while echidnas are omnivores with a wider range of diet.
In conclusion, hedgehogs and echidnas demonstrate divergent evolution due to their shared ancestry and subsequent adaptations to different environments. Their convergent evolution of spines highlights how similar pressures can lead to similar traits, even in distantly related species.