Fossil evidence for interbreeding between Neanderthals and modern humans

Lower jawbone discovered in 1957 could be from Neanderthal/modern human hybrid.

Although interbreeding between Neanderthals and modern humans has been inferred from genetic data, convincing fossil evidence for hybridisation has hitherto been lacking. Claims that the 24,500-year-old skeleton of a 4-year-old child found at Abrigo do Lagar Velho, Portugal in 1998 is an example of a hybrid (Duarte, et al., 1999) have not been widely accepted. Notably, the burial was typical of the Gravettian, a culture that is firmly associated with modern humans. It is possible that the infant was simply an unusually stocky modern human juvenile, or a ‘chunky child’ as one critic put it (Tattersall & Schwartz, 1999).

A newly-published report has claimed that a better case may be made for a lower jawbone from the Riparo Mezzena rocks helter, northern Italy. The jawbone was found in 1957, along with stone artefacts of the Mousterian tradition. As this tradition is firmly associated with Neanderthals in Europe, the 34,500-year-old jawbone was assumed to be Neanderthal. Mitochondrial DNA extracted from the jawbone confirms it to be Neanderthal. However, the Mezzena lower jawbone shows a number of modern features, including an incipient chin, which contrasts with the chinless jaws of ‘classic’ Neanderthals. The authors of the report claim that these features demonstrate hybridisation between Neanderthals and modern humans (Condemi, et al., 2013).

It is possible that the interbreeding occurred with a modern population thought to have been living at the nearby site of Grotta di Fumane (Longo, et al., 2012).

References:

1. Duarte, C. et al., The Early Upper Paleolithic Human Skeleton from the Abrigo do Lagar Velho (Portugal) and Modern Human Emergence in Iberia. PNAS 96, 7604–7609 (1999).

2. Tattersall, I. & Schwartz, J., Hominids and hybrids: The place of Neanderthals in human evolution. PNAS 96, 7117–7119 (1999).

3. Condemi, S. et al., Possible Interbreeding in Late Italian Neanderthals? New Data from the Mezzena Jaw (Monti Lessini, Verona, Italy). PLoS One 8 (3) (2013).

4. Longo, L. et al., Did Neandertals and anatomically modern humans coexist in northern Italy during the late MIS 3? Quaternary International 259, 102–112 (2012).

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Study highlights differences in brain organisation between Neanderthals and modern humans

Neanderthals focussed on vision at expense of social networking.

A new study has suggested that there were significant differences in the neurological organisation of Neanderthals and modern humans, reflecting physiological differences between the two species. Neanderthals, as has long been known, were larger and more powerfully-built than modern humans. Consequently, it is suggested that they required proportionately more ‘brain power’ to carry out body maintenance ‘housekeeping’ tasks and control functions. In addition, it is suggested that Neanderthals had larger eyes than modern humans, which also used up brain power. They lived at high latitudes in Eurasia, where they experienced lower light levels than people living in the tropics.

Researchers considered the remains of 21 Neanderthals and 38 modern humans dating from between 27 to 200 thousand years ago. They adjusted brain sizes to compensate for the greater Neanderthal body size, and estimated the size of the visual cortex from eye socket measurements. The average size of the Neanderthal eye socket was found to 44 by 36 mm (1.73 by 1.42 in.) compared with 42 by 30 mm (1.65 by 1.18 in.) for the modern humans. This equates to an eyeball volume of 34 cc against 29.5 cc; a 15 percent difference.

With more brain power required for housekeeping and visual functions, less would have been available for social interactions, and it has been suggested the Neanderthal maximum social group size was smaller than the ‘Dunbar Number’ of 150 associated with modern humans. The area covered by extended Neanderthal communities would have been smaller than those of modern humans. Their ability to trade would have been reduced, as would their capacity to learn of distant foraging areas potentially unaffected by local shortages. Furthermore, their ability to acquire and pass on innovations may have been limited in comparison to modern humans.

In the high latitudes of Eurasia, far from their African homeland, modern humans were disadvantaged in as much as they lacked the enhanced visual acuity, as well as other Neanderthal adaptations to the colder climate. Unable to adapt their bodies, modern humans adapted their technology, and thus became more reliant on it than were the Neanderthals. However, technological change can greatly outpace evolutionary change. The combination of adaptable technology and enhanced social networks gave the first modern humans in Europe a competitive advantage over the physically-adapted Neanderthals, eventually bringing about the demise of the latter.

References:

1. Pearce, E., Stringer, C. &  Dunbar, R., New insights into differences in brain organization between Neanderthals and anatomically modern humans. Proceedings of the Royal Society B 280 (1758) (2013).

Higher levels of Neanderthal ancestry in East Asians than in Europeans

A new study published in the journal Genetics (Wall et al, 2013) has concluded that East Asians have a higher level of Neanderthal DNA than do Europeans. The result implies that there was more than one episode of interbreeding between modern humans and Neanderthals.  After the ancestors of modern Europeans and East Asians separated, the latter population continued to interbreed with Neanderthals.

Given that the Neanderthals are thought to have been a predominantly Western Eurasian species, this result is unexpected. It is becoming clear that the history of interbreeding between modern humans and Neanderthals was rather more complex than was originally thought.

The paper is available open access – see this link on the Genetics website

References:
Wall, J., Yang, M., Jay, F., Kim, S., Durand, E., Stevison, L., Gignoux, C., Woerner, A., Hammer, M., and Slatkin, M. (2013) Higher levels of Neanderthal ancestry in East Asians than in Europeans, Genetics, Early Online

To Mars in a nutshell

O God, I could be bounded in a nutshell and count myself a king of infinite space…

Hamlet was not alluding to space travel, but he might as well have been. An audacious proposal announced by American millionaire Dennis Tito calls for a man and woman to make a 501-day round trip to Mars in a spacecraft half the size of a camper van. There will be no landing – the spacecraft will simply make a fly-by, skimming past the Red Planet at a minimum altitude of 100 miles. The crew are likely to be a middle-aged married couple.

Dennis Tito first made the headlines in 2001, when over the objections of NASA he paid for a seat on the Russian Soyuz TM-32 mission to the International Space Station. He was subsequently described as the first ‘space tourist’, a rather unfortunate label in my view. Tito, now 72, shares the frustration of all space enthusiasts at the complete lack of progress with the manned exploration of space since Project Apollo. It is now four decades since Cernan and Schmitt blasted off from the surface of the Moon. Nobody has been back; no manned spacecraft has left Earth orbit since.

There have been innumerable proposals for an expedition to Mars, but none have got off the ground even metaphorically. It is of course much harder to mount an expedition to Mars than it is to the Moon. The most obvious problem is that Mars is very much further away than the Moon. The Apollo missions typically lasted under ten days; the duration of Tito’s mission will be fifty times longer. The next problem is that Mars, though small in comparison to Earth, is still much larger than the Moon. Furthermore, unlike the Moon, it has a significant atmosphere. To land on Mars and take off again, you need a craft that is not only built for re-entry, but is also able to escape the higher Martian gravity on take-off. This means a craft that is considerably larger and more complex than the Apollo lunar module. The fuel requirements for the mission are immense. Assuming an Apollo-type lander-orbiter configuration, you need sufficient fuel for 1) the spacecraft to launch and leave Earth orbit, 2) achieve Martian orbit, 3) the lander to land and take-off, 4) the orbiter to leave Martian orbit, 5) make any required mid-course alterations.

The crucial difference between a manned expedition and the innumerable unmanned landers and rovers sent to Mars since the 1970s is that the latter don’t have to return to Earth. To date, no unmanned sample return mission to Mars has ever been attempted, and even attempts to return samples from its moons have failed. To get round the problem, some have suggested a one-way trip to Mars. Unlike the Moon, there are sufficient raw materials on Mars to allow colonists to keep themselves alive indefinitely. 

The Tito proposal involves a fly-by rather than a one-way trip. There’s no landing, but the crew don’t have to spend the rest of their lives on Mars. The spacecraft will be launched on a so-called free return trajectory, which will return it to Earth without the expenditure of fuel. Very little fuel will be needed after leaving Earth orbit. The result is a far simpler mission profile, though this term is relative. Unlike the International Space Station, which is periodically resupplied from Earth, the spacecraft will need to carry oxygen and supplies for the whole of the 501 day round trip. Even items such as toilet paper will amount to 28kg (62 lb.) in the supplies manifest. A major complication is that the spacecraft will be travelling at 51,000 km per hour (32,000 mph) when it returns to Earth. No manned spacecraft has ever attempted re-entry at such speed. It is likely that the spacecraft will have to slow down by aerobraking in the Earth’s outer atmosphere. The technique has been used for twenty years to slow unmanned space probes, but has never been attempted with a manned craft.

Another factor is radiation from the Sun and from interstellar space. A vehicle in Low Earth Orbit, such as the International Space Station or a shuttle, is largely protected by the Earth’s magnetic field. On a short-duration mission beyond Earth orbit – such as Apollo – the dosage is not large enough to be a problem. The possible effects of exposure on a long-duration mission include sterility and an elevated risk of developing cancer in later life. That is the reason for selecting a middle-aged crew. It is further assumed that a married couple could better endure the psychological stresses of long-term confinement.

There is also the risk of a coronal mass ejection from the Sun – a massive burst of radiation occurring during a solar flare. The proposed mission will take place during a period of low solar activity, but the risk isn’t entirely absent. The radiation could seriously harm or even kill the crew. Unfortunately, there is very little that can be done with present-day technology to shield a spacecraft against radiation. Finally, there is the stark reality that if something goes wrong with the spacecraft or if there is a medical emergency on-board, there will be absolutely nothing that can be done to abort the mission.

No concrete proposals yet exist for the mission. A possible configuration would involve a Dragon spacecraft from the private US space company Space X. The Dragon is a re-usable capsule-type craft that has already carried out an unmanned resupply mission to the International Space Station. The Dragon would be coupled to an inflatable habitat module of the type under development by Bigelow Aerospace, another private US space company. The mission would be launched with a Space X Falcon heavy-lift launch vehicle. First launch of the Falcon Heavy is expected either late this year or early next year.

The next launch window for the 501-day flight occurs in January 2018. After that, Mars will not be in the right position again until 2031. This gives Tito 5 years to get his mission off the ground. At the glacial speeds which NASA has operated since Apollo, this might not seem possible. However, it should be remembered that little over eight years passed from Alan Shepard’s sub-orbital spaceflight in 1961 to the late Neil Armstrong’s ‘giant leap for mankind’. The entire history of powered flight from Kittyhawk to the Sea of Tranquillity took place within the lifetime of many, including my grandparents.

The cost of the mission has been estimated at between $1 to 2 billion (£660 – 1200 million). This might sound like a lot of money, but it is actually less than Russian oligarch Roman Abramovich is alleged to have spent on Chelsea FC over the last decade. In space terms, it’s peanuts. In terms of actual Mars science, the value of the mission will be far less than can be achieved with unmanned orbiters and rovers. The scientific value of the mission will be in terms of what can be learned about the physiological and psychological effects of long-term spaceflight beyond Earth orbit.

The real worth of the mission, however, will be in its inspirational rather than scientific value. Nobody much under the age of 50 can remember the Moon landings. The current President of the United States was a few days short of his eighth birthday when Armstrong and Aldrin landed on the Moon; UK Prime Minister David Cameron was a 2 ½ year-old toddler. I think we’ve been waiting long enough for mankind’s next giant leap.

© Christopher Seddon 2013