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

Popular Posts

Indian shot (Canna indica)

Puspa midra or Indian shot ( Canna indica ) is is plant species in Cannaceae, annual, shrub 0.5-2.5 meters high, depending on variety, erect stems, unbranched and leaf midrib arranged overlapping to form pseudostems and hermaphrodite flowers. C. indica forms a branched rhizome, 60 cm long which is divided into rounded segments and is covered in two stripes by pale green or purple scaly leaves. The rhizome has tubers that contain very large starch grains. The surface has transverse furrows, the underside appears white roots and numerous shoots. The leaves sit alternate and spiral or arranged in two rows, very large and divided into a leaf midrib, short stalk and blade. The strands are 30-60 cm long, 10-20 cm wide and have linear veins, green or purple-green, the base blunt or narrowly pointed and the apex immediately tapering or sharp. Hermaphrodite flowers, pedicels 0.2-1 cm long and red or yellow-orange, except in some cultivars 4.5-7.5 cm long. The sepals are triangular in shape a...

Guinea grass (Panicum maximum)

Guinea grass or buffalo grass or green panic ( Panicum maximum ) is a plant species in Poaceae, annual grasses, growing upright to form clumps, strong, cultivated in all tropical and subtropical regions for very high value as fodder. P. maximum reproduces in very large pols, fibrous roots penetrate into the soil, upright stems, green, 1-1.5 m tall and have smooth cavities for diameters up to 2.5 mm. Propagation is done vegetatively and generatively. Ribbon-shaped leaves with a pointed tip, very many, built in lines, green, 40-105 cm long, 10-30 mm wide, erect, branched, a white linear bone, often covered with a layer of white wax, rough surface by hair short, dense and spread. The flower grows at the end of a long and upright stalk, open with the main axis length to more than 25 cm and the length of the bunches down to 20 cm. Grains have a size of 3x4 mm and oval. Seeds have a length of 2.25-2.50 mm and each 1 kg contains 1.2 - 1.5 million seeds. Guinea grass has two varieties. P...

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,...