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People walked like us 1.5 million years ago, study finds

Feb. 27, 2009
Courtesy Rutgers University
and World Science staff

New­found foot­prints show that early hu­mans walked like us, on an­a­tom­ic­ally mod­ern feet, 1.5 mil­lion years ago, sci­en­tists say.

Re­search­ers in­clud­ing an­thro­po­lo­g­ist W.K. Har­ris of Rut­gers, The State Uni­ver­s­ity of New Jer­sey, re­ported the find­ings in the in the Feb. 27 is­sue of the jour­nal Sci­ence.

A foot­print from Ile­ret, Ken­ya, dated as 1.5 mil­lion years old. (Im­age cour­te­sy Prof. Mat­thew Ben­nett, Bourne­mouth Uni­ver­si­ty, via Sc­ience/AAAS)

Har­ris di­rects a field school that the uni­ver­s­ity op­er­ates in col­la­bora­t­ion with the Na­tional Mu­se­ums of Ken­ya. From 2006 to 2008, the field school group of un­der­grad­u­ate stu­dents ex­ca­vat­ed the site yield­ing the foot­prints. 

The prints turned up in two 1.5 mil­lion-year-old rock lay­ers near Il­eret in north­ern Ken­ya. The rare im­pres­sions yielded in­forma­t­ion about soft tis­sue form and struc­ture not nor­mally ac­ces­si­ble in fos­sil­ized bones, ac­cord­ing to the re­search group, and are the old­est ev­i­dence of es­sen­tially mod­ern human-like foot anat­o­my. 

In the prints, the big toe is par­al­lel to the oth­er toes, un­like that of apes where it is sep­a­rat­ed in a grasp­ing con­figura­t­ion use­ful in trees, the in­ves­ti­ga­tors said. 

The foot­prints show a pro­nounced human-like arch and short toes, typ­ic­ally as­so­ci­at­ed with an up­right bi­pe­dal stance, they added. The size, spac­ing and depth of the im­pres­sions were the ba­sis of es­ti­mates of weight, stride and gait, all found to be with­in the range of mod­ern hu­mans.

The au­thors at­trib­ute the prints to the hom­i­nid spe­cies Ho­mo er­gas­ter, or early Ho­mo erec­tus as it’s more gen­er­ally known. This was the first hom­i­nid to have had the same body pro­por­tions as our spe­cies, mod­ern Ho­mo sapi­ens. Var­i­ous H. er­gas­ter or H. erec­tus re­mains have been found in Tan­za­nia, Ethi­o­pia, Ken­ya and South Af­ri­ca, with dates con­sist­ent with the Il­eret foot­prints.

Hominids are a family of pri­mate species that includes ours along with ex­tinct, hu­man­like crea­tures.

Oth­er hom­i­nid fos­sil foot­prints dat­ing to 3.6 mil­lion years ago had been dis­cov­ered in 1978 by Mary Lea­key at Lae­toli, Tan­za­nia. These are at­trib­uted to the less ad­vanced Aus­tra­lo­pith­e­cus afaren­sis, a pos­si­ble an­ces­tral hom­i­nid. The smaller, old­er Lae­toli prints show in­dica­t­ions of up­right pos­ture but pos­sess a shal­lower arch and a more ape-like, di­ver­gent big toe.

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Newfound footprints show that early humans walked like us, on anatomically modern feet, 1.5 million years ago, scientists say. Researchers including anthropologist W.K. Harris of Rutgers, The State University of New Jersey, reported the findings in the in the Feb. 27 issue of the journal Science. Harris directs a field school that the university operates in collaboration with the National Museums of Kenya. From 2006 to 2008, the field school group of undergraduate students excavated the site yielding the footprints. The prints turned up in two 1.5 million-year-old rock layers near Ileret in northern Kenya. The rare impressions yielded information about soft tissue form and structure not normally accessible in fossilized bones, according to the research group, and are the oldest evidence of essentially modern human-like foot anatomy. In the prints, the big toe is parallel to the other toes, unlike that of apes where it is separated in a grasping configuration useful in trees, the investigators said. The footprints also show a pronounced human-like arch and short toes, typically associated with an upright bipedal stance. The size, spacing and depth of the impressions were the basis of estimates of weight, stride and gait, all found to be within the range of modern humans. The authors attribute the prints to the hominid species Homo ergaster, or early Homo erectus as it is more generally known. This was the first hominid to have had the same body proportions as our species, modern Homo sapiens. Various H. ergaster or H. erectus remains have been found in Tanzania, Ethiopia, Kenya and South Africa, with dates consistent with the Ileret footprints. Other hominid fossil footprints dating to 3.6 million years ago had been discovered in 1978 by Mary Leakey at Laetoli, Tanzania. These are attributed to the less advanced Australopithecus afarensis, a possible ancestral hominid. The smaller, older Laetoli prints show indications of upright bipedal posture but possess a shallower arch and a more ape-like, divergent big toe.