Editing Directional selection (section)

==Timescale==
Typically directional selection acts strongly for short bursts and is not sustained over long periods of time.<ref>{{cite journal | last1=Hoekstra | first1=H. E. | last2=Hoekstra | first2=J. M. | last3=Berrigan | first3=D. | last4=Vignieri | first4=S. N. | last5=Hoang | first5=A. | last6=Hill | first6=C. E. | last7=Beerli | first7=P. | last8=Kingsolver | first8=J. G. | title=Strength and tempo of directional selection in the wild | journal=Proceedings of the National Academy of Sciences | volume=98 | issue=16 | date=2001-07-24 | issn=0027-8424 | doi=10.1073/pnas.161281098 | pages=9157–9160| pmid=11470913 | pmc=55389| bibcode=2001PNAS...98.9157H | doi-access=free }}</ref> If it was sustained, a population might hit [[biological constraints]] such that it no longer responds to selection. However, it is possible for directional selection to take a very long time to find a [[local optimum]] on a [[fitness landscape]].<ref>{{cite journal |last1=Kaznatcheev |first1=Artem |title=Computational Complexity as an Ultimate Constraint on Evolution |journal=Genetics |date=May 2019 |volume=212 |issue=1 |pages=245–265 |doi=10.1534/genetics.119.302000|pmid=30833289 |pmc=6499524 }}</ref> A possible example of long-term directional selection is the tendency of [[protein]]s to become more [[hydrophobicity scales|hydrophobic]] over time,<ref>{{cite journal |last1=Wilson |first1=Benjamin A. |last2=Foy |first2=Scott G. |last3=Neme |first3=Rafik |last4=Masel |first4=Joanna |title=Young genes are highly disordered as predicted by the preadaptation hypothesis of de novo gene birth |journal=Nature Ecology & Evolution |date=24 April 2017 |volume=1 |issue=6 |pages=0146–146 |doi=10.1038/s41559-017-0146|pmid=28642936 |pmc=5476217 |bibcode=2017NatEE...1..146W |url=https://repository.arizona.edu/bitstream/10150/627822/1/final_ISD_preprint.pdf |hdl=10150/627822 }}</ref> and to have their hydrophobic amino acids more interspersed along the [[protein primary structure|sequence]].<ref>{{cite journal |last1=Foy |first1=Scott G. |last2=Wilson |first2=Benjamin A. |last3=Bertram |first3=Jason |last4=Cordes |first4=Matthew H. J. |last5=Masel |first5=Joanna |title=A Shift in Aggregation Avoidance Strategy Marks a Long-Term Direction to Protein Evolution |journal=Genetics |date=April 2019 |volume=211 |issue=4 |pages=1345–1355 |doi=10.1534/genetics.118.301719|pmid=30692195 |pmc=6456324 }}</ref>