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Below are some science stories you may be interested in following this week. If you have any questions or feedback, please contact us at: info@sciencemedia.ca.
indicates Canadian contributors.

 Universal free fall leaves Einstein’s theory standing 
Nature
Embargoed until July 04, 2018 13:00 EDT (News release from Nature Research Press)
The principle that all objects accelerate identically, regardless of their own gravity, when falling in an external gravitational field has passed the most stringent test to date. Scientists observed the motions of a binary star system containing a neutron star closely orbited by a white dwarf, which are, in turn, both orbited by another, distant white dwarf. This triple-star system allowed investigation of how the pull of the outer white dwarf influences both the inner dwarf and its companion neutron star, which has strong self-gravity. The findings improve on previous tests of the equivalence principle of Einstein’s general theory of relativity by a factor of a thousand.
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Canadian co-author: Ingrid Stairs, University of British Columbia - stairs@astro.ubc.ca
 
Reproductive strategies linked to disease resistance in white-throated sparrows

Biology Letters
Embargoed until July 04, 2018 17:01 EDT (Brief from the Royal Society)
Disease resistance often comes at a cost to other functions, meaning that even within the same species, immune activity can differ between the sexes or even between different life-history strategies within a sex. White-throated sparrows are unusual in having two colour morphs, white and tan. Within each sex, white birds are more aggressive and tan birds provide more parental care. When researchers tested disease resistance in the two morphs, they found that – contrary to expectations – parasite loads were higher in tan birds, indicating that morph-associated immunity differences in sparrows could reflect fundamental differences in life history, not sex differences.
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Corresponding author: Elizabeth MacDougall-Shackleton, University of Western Ontario - emacdoug@uwo.ca
 
HPV testing detects cervical pre-cancer earlier, more accurately than Pap smear
JAMA
Embargoed until July 03, 2018 11:00 EDT (News release from JAMA)
Nearly all cervical cancers are associated with persistent cervical infection from cancer-related human papillomavirus (HPV) strains. Results from a randomized clinical trial of about 19,000 women that compared primary HPV testing alone versus Pap test for cervical screening show that primary HPV testing detects precancerous lesions earlier and more accurately than the Pap test. Moreover, women who were HPV negative were less likely than women screened by Pap tests to have cervical pre-cancer after four years.
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Corresponding author: Gina Suzanne Ogilvie, BC Women’s Hospital and Health Centre, Vancouver - gina.ogilvie@cw.bc.ca