Skip to main content

Temporal evidence shows Australopithecus sediba is unlikely to be the ancestor of Homo

Statistical analysis of fossil data shows that it is unlikely that Australopithecus sediba, a nearly two million year old, apelike fossil from South Africa, is the direct ancestor of Homo, the genus to which modern-day humans belong.

The research by Andrew Du and Zeresenay Alemseged from the University of Chicago, published in Science Advances, concludes by suggesting that Australopithecus afarensis, of the famous "Lucy" skeleton, is still the most likely ancestor to the genus Homo.

Dlium Temporal evidence shows Australopithecus sediba is unlikely to be the ancestor of Homo

The first A. sediba fossils were unearthed near Johannesburg in 2008. Hundreds of fragments of the species have since been discovered, all dating to roughly two million years ago. The oldest known Homofossil, the jawbone of an as yet unnamed species found in Ethiopia, is 2.8 million years old, predating A. sediba by 800,000 years.

Despite this timeline, the researchers who discovered A. sediba have claimed that it is an ancestral species to Homo. While it is possible that A. sediba (the hypothesized ancestor) could have postdated earliest Homo (the hypothesized descendant) by 800,000 years, the new analysis indicates that the probability of finding this chronological pattern is highly unlikely.

"It is definitely possible for an ancestor's fossil to postdate a descendant's by a large amount of time. We thought we would take it one step further to ask how likely it is to happen, and our models show that the probability is next to zero," said Du.

Du and Alemseged also reviewed the scientific literature for other hypothesized ancestor-descendant relationships between two hominin species. Of the 28 instances they found, only one first-discovered fossil of a descendant was older than its proposed ancestor, a pair of Homo species separated by 100,000 years, far less than the 800,000 years separating A. sediba and earliest Homo. For context, the average lifespan of any hominin species is about one million years.

"Again, we see that it's possible for an ancestor's fossil to postdate its descendant's. But 800,000 years is quite a long time," Du said.

Alemseged and Du maintain that Australopithecus afarensisis a better candidate for the direct ancestor of Homofor a number of reasons. A. afarensis fossils have been dated up to three million years old, nearing the age of the first Homo jaw.

"Given the timing, geography and morphology, these three pieces of evidence make us think afarensisis a better candidate than sediba," Alemseged said.

Lucy and her counterparts, including Selam, the fossil of an A. afarensischild that Alemseged discovered in 2000, were found in Ethiopia, just miles from where the Homo jaw was discovered. The jaw's features also resemble those of A. afarensis closely enough that one could make the case it was a direct descendant.

"One can disagree about morphology and the different features of a fossil, but the level of confidence we can put in the mathematical and statistical analyses of the chronological data in this paper makes our argument a very strong one," said Alemseged.

Journal : Andrew Du and Zeresenay Alemseged. Temporal evidence shows Australopithecus sediba is unlikely to be the ancestor of Homo, Science Advances, 08 May 2019, DOI:10.1126/sciadv.aav9038

Comments

Popular

Indian rosewood (Dalbergia latifolia)

Sonokeling or Java palisandre or Indian rosewood ( Dalbergia latifolia ) is a species of plant in the Fabaceae, a large tree producing hardwood, medium weight and high quality, rounded leaves, thin and broad pods, highly adaptive, grows in dry and rocky landscapes with lots of sunlight. D. latifolia has medium to large size, cylindrical stems, up to 40 m high with a ring of up to 2 m, the bark is brownish gray and slightly cracked longitudinally. The crown is dense, dome-shaped and sheds leaves. The leaves are compound and pinnate oddly with 5-7 strands that have different sizes and appear alternately on the shaft. The leaves are round or elongated in width or heart, the upper surface is green and the surface is pale green. The flowers are small, 0.5-1 cm long and clustered in panicles. The pods are green to brown when ripe and are elongated lanceolate, pointed at the base and tip. The pods have 1-4 seeds which are soft and brownish. Indian rosewood grows at elevations below 600 m,

Elephant bell gourd (Trichosanthes tricuspidata)

Elephant bell gourd ( Trichosanthes tricuspidata ) is a plant species in the Cucurbitaceae, stems grow elongated to propagate or climb, many branches, cylindrical in shape and green in color. T. cochinchinensis has stem tips or branches that twist to attach themselves to a support or other plant. It grows to climb to cover a support, usually on another plant, up to several meters and creeps along the ground to reach another support. Arrow-shaped leaves, split base, sharp apex and two wings at an acute angle, have many veins ending at a sharp edge, green and have a long petiole. Single flower is white. The fruit is round to oval, ends with a tail, young green and turns red with maturity, thin skin, thick flesh and reddish yellow, has a short stalk and hangs. The seeds are in the middle of the fruit. Seeds are white, oval and flat. Black coated seeds. Elephant bell gourd grows wild in primary and secondary forests, agricultural land, roadsides, watersheds, especially on slopes, damp a

Redflower ragleaf (Crassocephalum crepidioides)

Sintrong or ebolo or thickhead or redflower ragleaf ( Crassocephalum crepidioides ) are plant species in Asteraceae, terma height 25-100 cm, white fibrous roots, generally grow wild on the roadside, yard gardens or abandoned lands at altitude 200- 2500 m. C. crepidioides has erect or horizontal stems along the soil surface, vascular, soft, non-woody, shallow grooves, green, rough surface and short white hair, aromatic fragrance when squeezed. Petiole is spread on stems, tubular and eared. Single leaf, spread out, green, 8-20 cm long, 3-6 cm wide, longitudinal or round inverted eggshell with a narrow base along the stalk. Pointed tip, flat-edged or curved to pinnate, jagged rough and pointed. The top leaves are smaller and often sit. Compound flowers grow throughout the year in humps that are arranged in terminal flat panicles and androgynous. Green cuffs with orange-brown to brick-red tips, cylindrical for 13-16 mm long and 5-6 mm wide. The crown is yellow with a brownish red