Should they be considered the same species or separate species? Hooded crows and carrion crows look different, and largely mate within their own groups - but in some areas, they hybridize. The definition of a species as a group of interbreeding individuals cannot be easily applied to organisms that reproduce only or mainly asexually.Īlso, many plants, and some animals, form hybrids in nature. The bacterium shown at right is reproducing asexually, by binary fission. For example, many bacteria reproduce mainly asexually. That definition of a species might seem cut and dried, but it is not - in nature, there are lots of places where it is difficult to apply this definition. Happy face spider photos courtesy of Rosemary Gillespie, UC Berkeley. In this sense, a species is the biggest gene pool possible under natural conditions.įor example, these happy face spiders look different, but since they can interbreed, they are considered the same species: Theridion grallator.
The big issues – Pacing, diversity, complexity, and trends.
Macroevolution – Evolution above the species level.
Microevolution – Evolution within a population.Mechanisms: the processes of evolution – Selection, mutation, migration, and more.The history of life: looking at the patterns – Change over time and shared ancestors.An introduction to evolution: what is evolution and how does it work?.
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