Walking upright for 6 million years

National Geographic brings us the news that research indicated that our ancestors might have been walking upright for as long as six million years ago.

6-Million-Year-Old Human Ancestor 1st to Walk Upright?

An analysis of six-million-year-old bones from an early human ancestor that lived in what is now Kenya suggests that the species was the earliest known hominin to walk, a new study says.

The study that the National Geographic article refers to can be found here (behind the paywall at Science), and an Science article about it can be found here (again behind the paywall).

I can't really add anything to this, so please go read the articles.

What caused the changes in the size of shell ornaments?

This is a question being asked in a new paper in PLoS One

Climate Change, Genetics or Human Choice: Why Were the Shells of Mankind's Earliest Ornament Larger in the Pleistocene Than in the Holocene? by Peter R. Teske et al.

Background

The southern African tick shell, Nassarius kraussianus (Dunker, 1846), has been identified as being the earliest known ornamental object used by human beings. Shell beads dated from ~75,000 years ago (Pleistocene era) were found in a cave located on South Africa's south coast. Beads made from N. kraussianus shells have also been found in deposits in this region dating from the beginning of the Holocene era (<10,000 years ago). These younger shells were significantly smaller, a phenomenon that has been attributed to a change in human preference.

Methodology/Principal Findings

We investigated two alternative hypotheses explaining the difference in shell size: a) N. kraussianus comprises at least two genetic lineages that differ in size; b) the difference in shell size is due to phenotypic plasticity and is a function of environmental conditions. To test these hypotheses, we first reconstructed the species' phylogeographic history, and second, we measured the shell sizes of extant individuals throughout South Africa. Although two genetic lineages were identified, the sharing of haplotypes between these suggests that there is no genetic basis for the size differences. Extant individuals from the cool temperate west coast had significantly larger shells than populations in the remainder of the country, suggesting that N. kraussianus grows to a larger size in colder water.

Conclusion/Significance

The decrease in fossil shell size from Pleistocene to Holocene was likely due to increased temperatures as a result of climate change at the beginning of the present interglacial period. We hypothesise that the sizes of N. kraussianus fossil shells can therefore serve as indicators of the climatic conditions that were prevalent in a particular region at the time when they were deposited. Moreover, N. kraussianus could serve as a biomonitor to study the impacts of future climate change on coastal biota in southern Africa.

I will not claim that I think this is an amazing find, but it broadens our knowledge about our early ancestors, and the condition they lived under. On top of that, the findings can be used in other fiels, as the text I quoted above shows.

Go read the article over at PLoS One.

Is walking upright more energy efficient?

ScienceDaily reports on a new study that gives some evidence for the hypothesis that walking on two legs is more energy efficient than than dragging your knuckles while walking.

Study Identifies Energy Efficiency As Reason For Evolution Of Upright Walking

A new study provides support for the hypothesis that walking on two legs, or bipedalism, evolved because it used less energy than quadrupedal knucklewalking.

When I read that last night, while rather tired, my first thought was that that it sounded inplausible - if walking upright is more energy efficient, then why don't most mammals walk on two legs. Rereading it today, I of course realized that walking upright, like a Home Sapiens, is more energy efficient than walking on your legs and knuckles, like our fellow apes does. That doesn't mean that it's necessarily more efficient than walking on four legs, like the majority of mammals do.

Bipedalism marks a critical divergence between humans and other apes and is considered a defining characteristic of human ancestors. It has been hypothesized that the reduced energy cost of walking upright would have provided evolutionary advantages by decreasing the cost of foraging.

"For decades now researchers have debated the role of energetics and the evolution of bipedalism," said Raichlen. "The big problem in the study of bipedalism was that there was little data out there."

The researches collected metabolic, kinematic and kenetic data from five chimpanzees and four adult humans walking on a treadmill. The chimpanzees were trained to walk quadrupedally and bipedally on the treadmill.

Humans walking on two legs only used one-quarter of the energy that chimpanzees who knuckle-walked on four legs did. On average, the chimpanzees used the same amount of energy using two legs as they did when they used four legs. However, there was variability among chimpanzees in how much energy they used, and this difference corresponded to their different gaits and anatomy.

Interesting result, and it certainly explains why bipedalism became the movement of choice for Homo Sapiens and our ancestors. Or at least, it does so, once we moved down from the trees - I would expect that if we looked at movement in trees, the energy use would be somewhat reversed.

The study is published in PNAS, but unfortunately it's behind a pay-wall. The abstract can be found here though.