The_AT first_MD reliable_JJ analysis_NN1 of_IO cloud_NN1 behavior_NN1 over_II past_JJ decades_NNT2 suggests_VVZ --_JJ but_CCB falls_VVZ short_JJ of_IO proving_VVG --_NN1 that_CST clouds_NN2 are_VBR strongly_RR amplifying_VVG global_JJ warming_NN1 ._. 
If_CS that_DD1 's_VBZ true_JJ ,_, then_RT almost_RR all_DB climate_NN1 models_NN2 have_VH0 got_VVN it_PPH1 wrong_JJ ._. 
On_II page_NN1 460_MC ,_, climate_NN1 researchers_NN2 consider_VV0 the_AT two_MC best_RRT ,_, long-term_JJ records_NN2 of_IO cloud_NN1 behavior_NN1 over_II a_AT1 rectangle_NN1 of_IO ocean_NN1 that_CST nearly_RR spans_VVZ the_AT subtropics_NN1 between_II Hawaii_NP1 and_CC Mexico_NP1 ._. 
In_II a_AT1 warming_JJ episode_NN1 that_CST started_VVD around_RG 1976_MC ,_, ship-based_JJ data_NN showed_VVD that_DD1 cloud_NN1 cover_NN1 --_NN1 especially_RR low-altitude_JJ cloud_NN1 layers_NN2 --_NN1 decreased_VVN in_II the_AT study_NN1 area_NN1 as_CSA ocean_NN1 temperatures_NN2 rose_VVD and_CC atmospheric_JJ pressure_NN1 fell_VVD ._. 
One_MC1 interpretation_NN1 ,_, the_AT researchers_NN2 say_VV0 ,_, is_VBZ that_DD1 the_AT warming_JJ ocean_NN1 was_VBDZ transferring_VVG heat_NN1 to_II the_AT overlying_JJ atmosphere_NN1 ,_, thinning_VVG out_RP the_AT low-lying_JJ clouds_NN2 to_TO let_VVI in_RP more_DAR sunlight_NN1 that_DD1 further_RRR warmed_VVD the_AT ocean_NN1 ._. 
That_DD1 's_VBZ a_AT1 positive_JJ or_CC amplifying_VVG feedback_NN1 ._. 
During_II a_AT1 cooling_JJ event_NN1 in_II the_AT late_JJ 1990s_MC2 ,_, both_RR data_NN sets_NN2 recorded_VVD just_RR the_AT opposite_JJ changes_NN2 --_NN1 exactly_RR what_DDQ would_VM happen_VVI if_CSW the_AT same_DA amplifying_JJ process_NN1 were_VBDR operating_VVG in_II reverse_NN1 ._. 
Yes_UH ,_, the_AT moon_NN1 is_VBZ a_AT1 "_" wetter_JJR "_" place_NN1 than_CSN the_AT Apollo_NP1 astronauts_VVZ ever_RR could_VM have_VHI imagined_VVN ,_, but_CCB do_VD0 n't_XX break_VVI out_RP the_AT beach_NN1 gear_NN1 just_RR yet_RR ._. 
Although_CS three_MC independent_JJ groups_NN2 today_RT announced_VVD the_AT detection_NN1 of_IO water_NN1 on_II the_AT lunar_JJ surface_NN1 ,_, their_APPGE find_NN1 is_VBZ at_RR21 most_RR22 a_AT1 part_NN1 per_II 1000_MC water_NN1 in_II the_AT outermost_JJ millimeter_NN1 or_CC two_MC of_IO still_RR very_RG dry_JJ lunar_JJ rock_NN1 ._. 
The_AT discovery_NN1 has_VHZ potential_JJ ,_, though_RR ._. 
Future_JJ astronauts_NN2 might_VM conceivably_RR wring_VVI enough_DD water_NN1 from_II lunar_JJ "_" soil_NN1 "_" to_TO drink_VVI or_CC even_RR to_II fuel_NN1 their_APPGE rockets_NN2 ._. 
Equally_RR enticing_JJ ,_, the_AT water_NN1 seems_VVZ to_TO be_VBI on_II its_APPGE way_NN1 to_II the_AT poles_NN2 ,_, where_CS it_PPH1 could_VM be_VBI pumping_VVG up_RP subsurface_NN1 ice_NN1 deposits_NN2 that_CST would_VM be_VBI a_AT1 real_JJ water_NN1 bonanza_NN1 ._. 
A_AT1 less_RGR dry_JJ moon_NN1 makes_VVZ its_APPGE debut_NN1 courtesy_NN1 of_IO the_AT Moon_NN1 Mineralogy_NP1 Mapper_NP1 (_( M3_FO )_) that_CST has_VHZ been_VBN orbiting_VVG the_AT moon_NN1 onboard_NN1 India_NP1 's_GE now-defunct_JJ Chandrayaan-1_MC1 spacecraft_NN ._. 
A_AT1 spectrometer_NN1 ,_, M3_FO detected_VVD an_AT1 infrared_JJ absorption_NN1 at_II a_AT1 wavelength_NN1 of_IO 3.0_MC micrometers_NN2 that_CST only_JJ water_NN1 or_CC hydroxyl_NN1 --_NN1 a_AT1 hydrogen_NN1 and_CC an_AT1 oxygen_NN1 bound_VVD together_RL --_NN1 could_VM have_VHI created_VVN ._. 
But_CCB spectroscopists_NN2 had_VHD long_RR distrusted_VVN any_DD sign_NN1 of_IO water_NN1 in_II lunar_JJ data_NN because_CS Apollo_NP1 moon_NN1 rocks_NN2 were_VBDR so_RG bone-dry_JJ ._. 
So_RR M3_FO team_NN1 members_NN2 asked_VVD the_AT researchers_NN2 operating_VVG the_AT spectrometer_NN1 on_II NASA_NP1 's_GE EPOXI_JJ spacecraft_NN to_TO take_VVI a_AT1 look_NN1 as_CSA it_PPH1 passed_VVD the_AT moon_NN1 last_MD June_NPM1 on_II its_APPGE way_NN1 to_II comet_NN1 Hartley_NP1 2_MC ._. 
EPOXI_JJ observations_NN2 confirmed_VVD the_AT M3_FO detection_NN1 ,_, as_CSA did_VDD a_AT1 reanalysis_NN1 of_IO Cassini_JJ spectrometer_NN1 data_NN taken_VVN in_II 1999_MC on_II its_APPGE way_NN1 to_II Saturn_NP1 ._. 
The_AT three_MC analyses_NN2 are_VBR reported_VVN in_II separate_JJ papers_NN2 in_II tomorrow_RT 's_GE issue_NN1 of_IO Science_NN1 ._. 
The_AT discovery_NN1 "_" opens_VVZ up_RP a_AT1 whole_JJ different_JJ avenue_NN1 to_II a_AT1 source_NN1 of_IO water_NN1 on_II the_AT moon_NN1 ,_, "_" says_VVZ M3_FO principal_JJ investigator_NN1 Carle_NP1 Pieters_NP2 of_IO Brown_NP1 University_NN1 ._. 
EPOXI_JJ observations_NN2 show_VV0 the_AT water/hydroxyl_NN1 signal_NN1 coming_VVG and_CC going_VVG from_II the_AT surface_NN1 over_II days_NNT2 ,_, notes_VVZ Pieters_NP2 ,_, which_DDQ shows_VVZ that_CST there_EX 's_VBZ water_NN1 loosely_RR bound_VVN to_II surface_NN1 rock_NN1 ,_, not_XX just_RR tightly_RR bound_VVN hydroxyl_NN1 ._. 
The_AT best_JJT estimate_NN1 coming_VVG out_II21 of_II22 the_AT reported_JJ observations_NN2 for_IF water_NN1 's_GE abundance_NN1 is_VBZ 0.2_MC to_II 1_MC1 part_NN1 per_II 1000_MC of_IO water_NN1 ,_, she_PPHS1 says_VVZ ,_, and_CC that_DD1 's_VBZ in_II the_AT upper_JJ millimeter_NN1 or_CC two_MC that_DD1 spectroscopy_NN1 can_VM penetrate_VVI ._. 
At_II those_DD2 levels_NN2 ,_, an_AT1 astronaut_NN1 would_VM have_VHI to_TO process_VVI the_AT soil_NN1 from_II a_AT1 baseball-diamond-size_JJ plot_NN1 to_TO get_VVI a_AT1 decent_JJ drink_NN1 of_IO water_NN1 ._. 
More_RGR tantalizing_JJ ,_, the_AT water_NN1 becomes_VVZ more_RGR abundant_JJ closer_JJR to_II the_AT poles_NN2 ._. 
That_DD1 and_CC water_NN1 's_GE abundance_NN1 varying_VVG with_IW time_NNT1 suggests_VVZ to_II Pieters_NP2 that_CST water_NN1 is_VBZ being_VBG produced_VVN on_II the_AT moon_NN1 --_NN1 perhaps_RR through_II solar_JJ wind_NN1 hydrogen_NN1 interacting_VVG with_IW surface_NN1 rock_NN1 --_NN1 and_CC then_RT hopscotching_VVG from_II place_NN1 to_II place_NN1 through_II the_AT moon_NN1 's_GE vanishingly_RR thin_JJ atmosphere_NN1 ._. 
Because_CS a_AT1 water_NN1 molecule_NN1 would_VM stick_VVI more_RGR securely_RR to_II colder_JJR rock_NN1 ,_, water_NN1 would_VM tend_VVI to_TO migrate_VVI toward_II the_AT colder_JJR polar_JJ regions_NN2 ._. 
There_RL ,_, it_PPH1 might_VM become_VVI trapped_VVN for_IF eons_NN2 as_CSA subsurface_NN1 ice_NN1 in_II permanently_RR shadowed_JJ craters_NN2 ,_, which_DDQ are_VBR currently_RR thought_VVN to_TO be_VBI among_II the_AT coldest_JJT places_NN2 in_II the_AT solar_JJ system_NN1 ._. 
Come_VV0 9_MC October_NPM1 ,_, NASA_NP1 will_VM crash_VVI its_APPGE LCROSS_NN1 mission_NN1 into_II one_MC1 such_DA crater_NN1 in_II hopes_NN2 of_IO blasting_VVG water_NN1 into_II view_NN1 ._. 
"_" It_PPH1 's_VBZ very_RG exciting_JJ ,_, "_" says_VVZ planetary_JJ scientist_NN1 Dana_NP1 Hurley_NN1 of_IO the_AT Applied_JJ Physics_NN1 Laboratory_NN1 in_II Laurel_NP1 ,_, Maryland_NP1 ._. 
The_AT water_NN1 detection_NN1 "_" is_VBZ one_MC1 piece_NN1 of_IO the_AT puzzle_NN1 ;_; we_PPIS2 still_RR have_VH0 a_AT1 lot_NN1 of_IO pieces_NN2 missing_VVG ._. "_" 
Researchers_NN2 have_VH0 unveiled_VVN the_AT oldest_JJT known_JJ skeleton_NN1 of_IO a_AT1 putative_JJ human_JJ ancestor_NN1 --_NN1 and_CC it_PPH1 is_VBZ full_JJ of_IO surprises_NN2 ._. 
Although_CS the_AT creature_NN1 ,_, named_VVN Ardipithecus_NN1 ramidus_NN1 ,_, had_VHD a_AT1 brain_NN1 and_CC body_NN1 the_AT size_NN1 of_IO a_AT1 chimpanzee_NN1 ,_, it_PPH1 did_VDD not_XX knuckle-walk_JJ or_CC swing_VV0 through_II the_AT trees_NN2 like_II an_AT1 ape_NN1 ._. 
Instead_RR ,_, "_" Ardi_NP1 "_" walked_VVD upright_RL ,_, with_IW a_AT1 big_JJ ,_, stiff_JJ foot_NN1 and_CC short_JJ ,_, wide_JJ pelvis_NN1 ,_, researchers_NN2 report_VV0 in_II Science_NN1 ._. 
"_" We_PPIS2 thought_VVD Lucy_NP1 was_VBDZ the_AT find_NN1 of_IO the_AT century_NNT1 ,_, "_" says_VVZ paleoanthropologist_NN1 Andrew_NP1 Hill_NNL1 of_IO Yale_NP1 University_NN1 ,_, referring_VVG to_II the_AT famous_JJ 3.2-million-year-old_JJ skeleton_NN1 that_CST revolutionized_VVD thinking_VVG about_II human_JJ origins_NN2 ._. 
"_" But_CCB in_II retrospect_NN1 ,_, it_PPH1 was_VBDZ not_XX ._. "_" 
Researchers_NN2 have_VH0 long_RR argued_VVN about_II whether_CSW our_APPGE early_JJ ancestors_NN2 passed_VVN through_II a_AT1 great-ape_JJ stage_NN1 in_II which_DDQ they_PPHS2 looked_VVD like_II protochimpanzees_NN2 ,_, with_IW short_JJ backs_NN2 ;_; arms_NN2 adapted_VVN for_IF swinging_VVG through_II the_AT trees_NN2 ;_; and_CC a_AT1 pelvis_NN1 and_CC limbs_NN2 adapted_VVN for_IF knuckle-walking_NN1 (_( Science_NN1 ,_, 21_MC November_NPM1 1969_MC ,_, p._NN1 953_MC )_) ._. 
This_DD1 "_" troglodytian_NN1 ,_, "_" or_CC chimpanzee_NN1 ,_, model_NN1 for_IF early_JJ human_JJ behavior_NN1 (_( named_VVN for_IF the_AT common_JJ chimpanzee_NN1 ,_, Pan_NP1 troglodytes_NN2 )_) suggests_VVZ that_CST our_APPGE ancestors_NN2 lost_VVD many_DA2 of_IO the_AT key_JJ adaptations_NN2 still_RR found_VVN in_II chimpanzees_NN2 ,_, bonobos_NN2 ,_, and_CC gorillas_NN2 ,_, such_II21 as_II22 daggerlike_JJ canines_NN2 and_CC knuckle-walking_NN1 ,_, which_DDQ those_DD2 apes_NN2 were_VBDR thought_VVN to_TO have_VHI inherited_VVN from_II a_AT1 common_JJ ancestor_NN1 ._. 
Evidence_NN1 has_VHZ been_VBN hard_JJ to_TO come_VVI by_II ,_, however_RR ,_, because_CS there_EX are_VBR almost_RR no_AT fossils_NN2 of_IO early_JJ chimpanzees_NN2 and_CC gorillas_NN2 ._. 
Until_II now_RT ,_, the_AT oldest_JJT known_JJ skeleton_NN1 of_IO a_AT1 human_JJ ancestor_NN1 was_VBDZ Lucy_NP1 ,_, who_PNQS proved_VVD in_II one_MC1 stroke_NN1 that_CST our_APPGE ancestors_NN2 walked_VVD upright_RL before_CS they_PPHS2 evolved_VVD big_JJ brains_NN2 ._. 
But_CCB at_II 3.2_MC million_NNO years_NNT2 old_JJ ,_, she_PPHS1 was_VBDZ too_RG recent_JJ and_CC already_RR too_RG much_DA1 like_II a_AT1 human_JJ to_TO reveal_VVI much_RR about_II her_APPGE primitive_JJ origins_NN2 ._. 
As_II a_AT1 result_NN1 ,_, researchers_NN2 have_VH0 wondered_VVN since_CS her_APPGE discovery_NN1 in_II 1974_MC ,_, what_DDQ came_VVD before_II her_APPGE --_NN1 what_DDQ did_VDD the_AT early_JJ members_NN2 of_IO the_AT human_JJ family_NN1 look_VV0 like_II ?_? 
The_AT footprints_NN2 they_PPHS2 left_VVD behind_RL ,_, the_AT second_MD oldest_JJT ever_RR found_VVN ,_, reveal_VV0 that_CST these_DD2 early_JJ humans_NN2 had_VHD evolved_VVN big_JJ ,_, modern_JJ feet_NN2 --_NN1 and_CC that_CST they_PPHS2 walked_VVD just_RR like_VV0 we_PPIS2 do_VD0 ,_, according_II21 to_II22 a_AT1 new_JJ study_NN1 ._. 
Human_JJ ancestors_NN2 began_VVD walking_VVG upright_RL at_RR21 least_RR22 6_MC million_NNO years_NNT2 ago_RA ,_, according_II21 to_II22 analysis_NN1 of_IO hominid_JJ leg_NN1 and_CC pelvic_JJ bones_NN2 ._. 
But_CCB researchers_NN2 have_VH0 debated_VVN when_CS they_PPHS2 evolved_VVD the_AT ability_NN1 to_TO walk_VVI upright_RL in_II a_AT1 modern_JJ manner_NN1 ,_, rather_CS21 than_CS22 with_IW a_AT1 more_RGR primitive_JJ gait_NN1 ,_, possibly_RR like_II the_AT bent-kneed_JJ waddle_NN1 of_IO chimpanzees_NN2 ._. 
Footprints_NN2 found_VVN in_II Laetoli_NP1 ,_, Tanzania_NP1 ,_, show_VV0 that_CST the_AT australopithecines_NN2 that_CST made_VVD them_PPHO2 3.75_MC million_NNO years_NNT2 ago_RA had_VHD longer_JJR toes_NN2 ,_, a_AT1 shallower_JJR arch_NN1 ,_, and_CC a_AT1 more_RGR apelike_JJ big_JJ toe_NN1 that_CST jutted_VVD slightly_RR away_II21 from_II22 the_AT other_JJ toes_NN2 ._. 
This_DD1 suggested_VVD to_II some_DD that_CST they_PPHS2 had_VHD a_AT1 more_RGR primitive_JJ gait_NN1 and_CC that_CST the_AT transition_NN1 to_II fully_RR modern_JJ walking_NN1 did_VDD n't_XX happen_VVI until_CS our_APPGE direct_JJ ancestor_NN1 ,_, Homo_NP1 erectus_NN1 ,_, emerged_VVD about_RG 1.9_MC million_NNO years_NNT2 ago_RA ._. 
However_RR ,_, researchers_NN2 had_VHD few_DA2 fossils_NN2 of_IO the_AT foot_NN1 of_IO H._NP1 erectus_NN1 to_TO prove_VVI it_PPH1 walked_VVD just_RR like_VV0 we_PPIS2 do_VD0 ._. 
Now_RT ,_, with_IW the_AT discovery_NN1 of_IO the_AT footprints_NN2 ,_, which_DDQ were_VBDR probably_RR made_VVN by_II H._NP1 erectus_NN1 ,_, at_II Ileret_NP1 ,_, they_PPHS2 have_VH0 direct_JJ evidence_NN1 of_IO how_RRQ it_PPH1 walked_VVD ._. 
To_TO find_VVI out_RP ,_, a_AT1 team_NN1 led_VVN by_II Matthew_NP1 Bennett_NP1 of_IO Bournemouth_NP1 University_NN1 in_II the_AT United_NP1 Kingdom_NP1 scanned_VVD and_CC digitized_VVD at_RR21 least_RR22 four_MC trails_NN2 of_IO footprints_NN2 laid_VVN down_RP over_II several_DA2 thousand_NNO years_NNT2 at_II Ileret_NP1 ._. 
The_AT researchers_NN2 were_VBDR able_JK to_TO use_VVI the_AT size_NN1 ,_, spacing_VVG ,_, and_CC depth_NN1 of_IO the_AT impressions_NN2 to_TO estimate_VVI the_AT weight_NN1 ,_, stride_VV0 length_NN1 ,_, and_CC gait_NN1 of_IO the_AT ancient_JJ walkers_NN2 ._. 
As_II the_AT researchers_NN2 report_VV0 in_RP tomorrow_RT 's_GE issue_NN1 of_IO Science_NN1 ,_, the_AT new_JJ footprints_NN2 show_VV0 that_CST these_DD2 early_JJ humans_NN2 were_VBDR pushing_VVG off_II the_AT ground_NN1 with_IW their_APPGE big_JJ toes_NN2 --_NN1 or_CC toeing_VVG off_II --_NN1 and_CC shifting_VVG their_APPGE weight_NN1 over_II these_DD2 digits_NN2 in_II the_AT same_DA way_NN1 as_CSA modern_JJ humans_NN2 ._. 
H._NP1 erectus_NN1 's_GE feet_NN2 had_VHD clearly_RR evolved_VVN a_AT1 modern_JJ shape_NN1 ,_, with_IW the_AT big_JJ toe_NN1 parallel_NN1 to_II the_AT other_JJ toes_NN2 and_CC a_AT1 pronounced_JJ arch_NN1 ,_, says_VVZ paleoanthroologist_NN1 Brian_NP1 Richmond_NP1 of_IO George_NP1 Washington_NP1 University_NN1 in_II Washington_NP1 ,_, D.C._NP1 In_II31 addition_II32 to_II33 finding_VVG the_AT human_JJ footprints_NN2 ,_, the_AT researchers_NN2 also_RR found_VVN tracks_NN2 of_IO ancient_JJ animals_NN2 ,_, from_II birds_NN2 to_II lions_NN2 ,_, that_CST provide_VV0 a_AT1 "_" snapshot_NN1 in_II time_NNT1 of_IO what_DDQ animals_NN2 were_VBDR on_II the_AT landscape_NN1 ,_, "_" says_VVZ paleoanthropologist_NN1 and_CC co-author_NN1 John_NP1 Harris_NP1 of_IO Rutgers_NP1 University_NN1 ,_, New_NP1 Brunswick_NP1 ._. 
The_AT new_JJ glimpse_NN1 of_IO the_AT footpaths_NN2 of_IO animals_NN2 and_CC humans_NN2 complement_VV0 earlier_JJR studies_NN2 that_CST reveal_VV0 the_AT anatomy_NN1 and_CC behavior_NN1 of_IO H._NP1 erectus_NN1 ,_, suggesting_VVG that_CST as_CSA it_PPH1 evolved_VVD modern_JJ body_NN1 proportions_NN2 ,_, it_PPH1 also_RR increased_VVD its_APPGE home_NN1 range_NN1 and_CC began_VVD competing_VVG with_IW carnivores_NN2 for_IF carcasses_NN2 on_II the_AT savanna_NN1 ,_, says_VVZ Harris_NP1 ._. 
Other_JJ scientists_NN2 agree_VV0 that_CST the_AT prints_NN2 expose_VV0 the_AT steps_NN2 our_APPGE ancestors_NN2 took_VVD on_RP the_AT way_NN1 to_II becoming_VVG modern_JJ ._. 
"_" Fossil_NN1 footprints_NN2 are_VBR literally_RR frozen_JJ behavior_NN1 ,_, "_" says_VVZ anatomist_NN1 William_NP1 Jungers_NP1 of_IO Stony_JJ Brook_NN1 University_NN1 Medical_JJ Center_NN1 in_II New_NP1 York_NP1 state_NN1 ._. 
"_" They_PPHS2 confirm_VV0 that_CST a_AT1 modern_JJ ,_, humanlike_JJ ,_, bipedal_JJ gait_NN1 is_VBZ present_JJ by_II at_RR21 least_RR22 1.5_MC million_NNO years_NNT2 ago_RA ,_, with_IW all_DB the_AT biomechanical_JJ nuances_NN2 we_PPIS2 associate_VV0 with_IW our_APPGE own_DA way_NN1 of_IO walking_NN1 ._. "_" 
But_CCB the_AT shoulder_NN1 and_CC pelvis_NN1 of_IO H._NP1 erectus_NN1 were_VBDR still_RR primitive_JJ ,_, says_VVZ Jungers_NP1 ,_, so_CS the_AT footprints_NN2 also_RR show_VV0 that_CST on_II the_AT path_NN1 to_II modernity_NN1 ,_, "_" the_AT foot_NN1 led_VVD the_AT way_NN1 ._. "_" 
Although_CS humans_NN2 come_VV0 in_II many_DA2 shapes_NN2 and_CC sizes_NN2 ,_, from_II the_AT compact_JJ Inuit_NN1 of_IO the_AT Arctic_JJ to_II the_AT willowy_JJ Masai_NP1 warriors_NN2 of_IO Africa_NP1 ,_, any_DD two_MC people_NN are_VBR a_RR21 lot_RR22 more_RGR alike_RR genetically_RR than_CSN any_DD pair_NN of_IO chimpanzees_NN2 or_CC gorillas_NN2 ._. 
The_AT reason_NN1 may_VM be_VBI our_APPGE advanced_JJ culture_NN1 ,_, according_II21 to_II22 a_AT1 new_JJ study_NN1 ._. 
Our_APPGE ancestors_NN2 '_GE different_JJ tools_NN2 ,_, eating_NN1 habits_NN2 ,_, and_CC even_RR body_NN1 decorations_NN2 limited_VVN their_APPGE mate_NN1 choices_NN2 to_II individuals_NN2 of_IO a_AT1 similar_JJ culture_NN1 ,_, the_AT work_NN1 suggests_VVZ ,_, reducing_VVG the_AT spread_NN1 of_IO new_JJ mutations_NN2 across_II many_DA2 groups_NN2 ._. 
Because_CS only_RR a_AT1 few_DA2 of_IO these_DD2 ancient_JJ groups_NN2 survived_VVD ,_, humans_NN2 are_VBR much_RR less_RGR genetically_RR diverse_JJ than_CSN other_JJ primates_NN2 ,_, even_CS21 though_CS22 there_EX are_VBR many_DA2 more_DAR of_IO us_PPIO2 on_II the_AT planet_NN1 ._. 
Ever_RR since_CS researchers_NN2 discovered_VVD in_II the_AT 1970s_MC2 that_CST humans_NN2 lacked_VVD the_AT genetic_JJ variation_NN1 expected_VVN of_IO our_APPGE population_NN1 size_NN1 ,_, they_PPHS2 have_VH0 proposed_VVN that_CST our_APPGE ancestors_NN2 went_VVD through_II a_AT1 big_JJ squeeze_NN1 :_: Volcanic_JJ eruptions_NN2 ,_, disease_NN1 ,_, or_CC climate_NN1 change_NN1 created_VVD a_AT1 population_NN1 "_" bottleneck_NN1 "_" that_CST reduced_VVD the_AT number_NN1 of_IO breeding_NN1 adults_NN2 to_II about_RG 10,000_MC sometime_JJ in_II the_AT past_JJ 100,000_MC years_NNT2 ._. 
But_CCB new_JJ genetic_JJ studies_NN2 of_IO ancient_JJ DNA_NN1 from_II Neandertals_NP1 have_VH0 found_VVN that_CST they_PPHS2 and_CC the_AT last_MD ancestor_NN1 they_PPHS2 shared_VVD with_IW humans_NN2 ,_, about_RG 600,000_MC years_NNT2 ago_RA ,_, also_RR lacked_VVD much_RR genetic_JJ variation_NN1 ,_, which_DDQ would_VM require_VVI at_RR21 least_RR22 three_MC dramatic_JJ bottlenecks_NN2 --_NN1 an_AT1 improbable_JJ scenario_NN1 ._. 
Meanwhile_RR ,_, other_JJ studies_NN2 have_VH0 found_VVN that_DD1 language_NN1 differences_NN2 restricted_JJ gene_NN1 flow_NN1 in_II recent_JJ times_NNT2 in_II Europe_NP1 ,_, suggesting_VVG that_DD1 cultural_JJ barriers_NN2 might_VM have_VHI limited_VVN genetic_JJ diversity_NN1 more_RGR consistently_RR than_CSN occasional_JJ local_JJ bottlenecks_NN2 ._. 
Paleoanthropologists_NP1 Jean-Jacques_NP1 Hublin_NP1 and_CC Luke_NP1 Premo_NN1 of_IO the_AT Max_NP1 Planck_NP1 Institute_NN1 for_IF Evolutionary_JJ Anthropology_NN1 in_II Leipzig_NP1 ,_, Germany_NP1 ,_, tested_VVD this_DD1 hypothesis_NN1 by_II simulating_VVG how_RGQ mating_JJ preferences_NN2 alter_VV0 gene_NN1 flow_NN1 between_II individuals_NN2 in_II different_JJ groups_NN2 ._. 
Genetic_JJ variability_NN1 plunged_VVD when_RRQ individuals_NN2 required_JJ mates_NN2 with_IW the_AT highest_JJT degree_NN1 of_IO cultural_JJ similarity_NN1 ,_, the_AT team_NN1 reports_VVZ this_DD1 week_NNT1 in_II The_AT Proceedings_NN2 of_IO the_AT National_JJ Academy_NN1 of_IO Sciences_NN2 ._. 
Conversely_RR ,_, genetic_JJ diversity_NN1 increased_VVN when_CS individuals_NN2 were_VBDR less_RGR selective_JJ about_II their_APPGE mates_NN2 --_JJ as_CSA is_VBZ the_AT case_NN1 in_II chimpanzees_NN2 or_CC gorillas_NN2 ,_, which_DDQ mate_NN1 whenever_RRQV possible_JJ with_IW individuals_NN2 from_II other_JJ groups_NN2 ._. 
Hublin_NN1 and_CC Premo_NP1 propose_VV0 that_CST if_CS human_JJ ancestors_NN2 selected_JJ mates_NN2 from_II similar_JJ backgrounds_NN2 ,_, there_EX would_VM have_VHI been_VBN a_AT1 lot_NN1 of_IO inbreeding_NN1 within_II different_JJ populations_NN2 ,_, restricting_VVG the_AT flow_NN1 of_IO new_JJ mutations_NN2 to_II other_JJ groups_NN2 ._. 
"_" If_CS these_DD2 guys_NN2 on_II the_AT other_JJ side_NN1 of_IO the_AT river_NN1 spoke_VVD a_AT1 different_JJ language_NN1 and_CC had_VHD different_JJ weapons_NN2 ,_, you_PPY would_VM not_XX try_VVI to_TO mate_VVI with_IW them_PPHO2 or_CC they_PPHS2 might_VM kill_VVI you_PPY ,_, "_" says_VVZ Hublin_NP1 ._. 
Over_II time_NNT1 ,_, most_DAT populations_NN2 went_VVD extinct_JJ ,_, allowing_VVG the_AT genes_NN2 of_IO only_RR a_AT1 few_DA2 groups_NN2 to_TO proliferate_VVI ,_, further_RRR erasing_VVG genetic_JJ diversity_NN1 ._. 
Researchers_NN2 who_PNQS have_VH0 long_RR worked_VVN on_II this_DD1 problem_NN1 are_VBR eager_JJ to_TO test_VVI the_AT new_JJ hypothesis_NN1 in_II living_JJ hunter-gatherers_NN2 ._. 
Paleoanthropologist_NP1 John_NP1 Hawks_NN2 of_IO the_AT University_NN1 of_IO Wisconsin_NP1 ,_, Madison_NP1 ,_, for_REX21 example_REX22 ,_, plans_VVZ to_TO ask_VVI his_APPGE students_NN2 to_TO determine_VVI whether_CSW there_EX 's_VBZ more_DAR intermarriage_NN1 between_II hunter-gatherer_JJ groups_NN2 that_CST live_VV0 close_VV0 together_RL and_CC ,_, therefore_RR ,_, are_VBR likely_JJ to_TO have_VHI similar_JJ cultures_NN2 ._. 
Biological_JJ anthropologist_NN1 Henry_NP1 Harpending_NP1 of_IO the_AT University_NN1 of_IO Utah_NP1 in_II Salt_NP1 Lake_NP1 City_NN1 also_RR likes_VVZ the_AT new_JJ explanation_NN1 for_IF the_AT missing_JJ mutations_NN2 :_: "_" It_PPH1 is_VBZ time_NNT1 that_CST human_JJ population_NN1 geneticists_NN2 recover_VV0 from_II waving_VVG the_AT magic_JJ wand_NN1 of_IO 'bottleneck'_JJ to_TO try_VVI to_TO explain_VVI everything_PN1 ._. "_" 
