Speciation?

Question

1. How can disruptive selection lead to speciation in sympatric populations of the same species?

My book isn't helping & I'm looking online but I haven't found anything useful yet. Please don't copy and paste things from wikipedia or anything... that doesn't help me understand, and their examples are confusing. Thank You.

Answer 1

If you have two divergent forces of selection operating on one population, you may get divergence and speciation in sympatry. For a hypothetical example, imagine a population of birds in an environment where there are big seeds that require big beaks to crack them, and small seeds that require long, narrow beaks to crack them. There will be opposing selective pressures imposed by the two kinds of food: one source selects for big beaks, one for small. If there is variation in beak size present in the population to start with, you might get a splitting of the population where birds with different beak sizes split to feed on different seeds.
This could then, hypothetically, lead to behavioral differences between feeding times and locations, which might lead to assortative mating. This in turn could, with the help of mutation and genetic drift, start to lead to genetic divergence.

Hope this helps, sympatric speciation is a very tricky thing to prove and to get a handle on.

If you want to read about it, look up apple hawthorn maggots--they are a type of fly which are believed to have split into two species in sympatry in the United States.

Answer 2

Micro-evolution is defined as the change of allele frequencies within a population over time and can include speciation within the kind. Even a mutation creating a new allele falls within this definition since the organism remains in the same kind. Macro-evolution requires the formation of new genetic information and changes beyond the boundaries of the kind. If you are after Creationist justification for these definitions it is that God created all things to reproduce after their kind. Even Linnaeus recognised that kind did not correspond exactly with his taxonomic divisions. Yes I have looked at the TO list of speciation and they are all within the existing kind and are examples of micro-evolution. Biologists have trouble precisely defining species and creationists have trouble determining the boundaries of kind. That doesn't make either concept unusable. Evolutionists are also adept at changing the definitions of their terms (such as vestigial) so Creationists need not apologise for refining their definitions where necessary as biological knowledge improves.