SPECIATION
- Minor genetic changes occurring in a population are called microevolution. They change the common characteristics of a species but cannot explain the formation of new species.
- Speciation is an evolutionary process of forming new species.
- If a population splits into two such that they cannot reproduce with each other, they are called two species. This can be explained using a beetle population.
- Consider a huge beetle population spread over a mountain range. Here, each beetle feeds mostly on nearby bushes. They do not travel far, so there will be sub-populations in neighborhoods.
- Most reproduction occurs within these sub-populations.
- In rare cases, some beetles might go from one site to another, or a crow picks up a beetle from one site to another. As a result, the genes of the migrant beetle enter the new population by reproduction and cause genetic drift (accidental genetic variation in a small population).
- If a large river comes between two sub-populations, they will be isolated. Thus, gene flow between them decreases.
- Over generations, genetic drift accumulates many changes in each sub-population. Also, natural selection operates in these different geographic locations. For example, in one sub-population, crows are eliminated by eagles, so the green beetle variation will not be selected. But in another sub-population, the number of crows is very high, so the green variation will be strongly selected.
- Genetic drift and natural selection together make isolated sub-populations more and more different. Eventually, members of these two groups will be incapable of reproducing with each other, even if they happen to meet. This can happen in many ways:
- If the DNA changes are significant (e.g., a change in the number of chromosomes), the germ cells of the two groups cannot fuse.
- A new variation may emerge in which green females will not mate with red males, but only with green males (natural selection for greenness). Thus, new species of beetles are generated.
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1. Accumulation of Variation, Heredity 2. Evolution 3. Speciation 4. Evolution & Classification