Reduction of gene flow. However, speciation might also happen in a population with no specific extrinsic barrier to gene flow. Imagine a situation in which a population extends over a broad geographic range, and mating throughout the population is not random.
The Internal Revenue Service places restrictions on how far back you can amend your tax return, regardless of whether you owed tax or received a refund. Filers must use Form 1040X to amend a return and should only file an amendment to report certain changes. You have three years from the due date of the original return or two years from when you paid tax owing to submit an amended return. A pen next to an income tax form.
The statute of limitations on how far back the IRS can audit (called the Assessment Statute Expiration Date or ASED) varies depending upon the circumstances of the tax return. In most cases the IRS will not go back more than 3 years unless there is something very wrong with the tax return that was filed.