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Descent of Man In this lecture, beginners can familiarize themselves with basic information and terms used to describe the evolution of humanity beginning with the origin of primates through the comings and goings of Genus Homo. |
Growth Study Of Wild Chimpanzees Challenges Assumptions About Early Humans
Posted: Thursday, July 15, 2004
Source: University Of California - Santa Cruz
SANTA CRUZ, CA -- A new study of wild chimpanzee growth rates, published in the Early Edition of the Proceedings of the National Academy of Sciences (http://www.pnas.org/), suggests that early human evolution may have taken a different course than is widely believed.
The results challenge the assumption that human evolution followed a path from a chimplike ancestor to a transitionary Homo erectus and then Homo sapiens, suggesting instead that chimpanzees have more in common developmentally with Homo erectus and that modern humans are the "out-group."
The study was coauthored by Adrienne Zihlman, professor of anthropology at the University of California, Santa Cruz; Debra Bolter, who just earned her doctorate in anthropology at UCSC; and Christophe Boesch, director of primatology at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
The researchers examined skeletal samples from 18 wild chimpanzees of known ages and compared the data to the dentition of captive chimpanzees, which have been used as a baseline for discussion of hominid origins and the transition from ape ancestors to hominids. The eruption of teeth mark other life events, such as completion of brain growth (90 to 95 percent of brain growth is complete when the first permanent molar erupts) and life-history stages like infancy, juvenile, and adulthood.
The team's analysis consistently showed a slower rate of development of all the teeth of wild chimpanzees compared to captive chimpanzees: Among wild chimpanzees, infancy lasted until about four years of age and mature dentition was reached between 12 and 13 years of age, compared to captive animals whose infancy ended around three years of age and who reached mature dentition about 10 years of age.
"These findings challenge a number of assumptions about the growth of hominids," said Zihlman. "Anthropologists and paleoanthropologists have relied heavily on studies of captive chimpanzees to establish a baseline for hominid growth and to generate hypotheses about the life history and behaviors of fossil humans. We now know those scenarios are based on faulty data."
Comparing teeth of wild chimpanzees to previous research on two Homo erectus fossil specimens, the researchers found that the first molars of both wild chimpanzees and Homo erectus emerge at about four years of age, and the second molars emerge at about eight years of age.
"Our data suggest that wild chimpanzees and Homo erectus growth patterns may not have differed from each other as much as previously thought," said Zihlman. "These findings do not support Homo erectus developmentally as an intermediate between chimplike ancestors and modern humans. Our data also call into question the assumption that a larger body size and a big brain require a longer time to grow."
The findings also explain why dental-eruption data derived from captive chimpanzees didn't match the life stages of wild animals observed by researchers in the field, Zihlman noted.
The skeletal samples examined included 12 immature individuals and one young adult from the Tai National Park, Ivory Coast, four immatures from Gombe National Park in Tanzania, and one immature from Bossou, Guinea.
The paper, "Wild Chimpanzee Dentition and its Implications for Assessing Life History in Immature Hominin Fossils," is scheduled to appear in the July 20 print edition of the Proceedings of the National Academy of Science.
www.ucsc.edu/news_events/press_releases/text.asp?pid=526
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Posted: Wednesday, July 7, 2004
Source: European Southern Observatory
Very Large Telescope Unravels New Population of Very Old Massive Galaxies
Summary
Current theories of the formation of galaxies are based on the hierarchical merging of smaller entities into larger and larger structures, starting from about the size of a stellar globular cluster and ending with clusters of galaxies. According to this scenario, it is assumed that no massive galaxies existed in the young universe.
However, this view may now have to be revised. Using the multi-mode FORS2 instrument on the Very Large Telescope at Paranal, a team of Italian astronomers [2] have identified four remote galaxies, several times more massive than the Milky Way galaxy, or as massive as the heaviest galaxies in the present-day universe. Those galaxies must have formed when the Universe was only about 2,000 million years old, that is some 12,000 million years ago.
The newly discovered objects may be members of a population of old massive galaxies undetected until now.
The existence of such systems shows that the build-up of massive elliptical galaxies was much faster in the early Universe than expected from current theory.
Hierarchical merging
Galaxies are like islands in the Universe, made of stars as well as dust and gas clouds. They come in different sizes and shapes. Astronomers generally distinguish between spiral galaxies - like our own Milky Way, NGC 1232 or the famous Andromeda galaxy - and elliptical galaxies, the latter mostly containing old stars and having very little dust or gas. Some galaxies are intermediate between spirals and ellipticals and are referred to as lenticular or spheroidal galaxies.
Galaxies are not only distinct in shape, they also vary in size: some may be as "light" as a stellar globular cluster in our Milky Way (i.e. they contain about the equivalent of a few million Suns) while others may be more massive than a million million Suns. Presently, more than half of the stars in the Universe are located in massive spheroidal galaxies.
One of the main open questions of modern astrophysics and cosmology is how and when galaxies formed and evolved starting from the primordial gas that filled the early Universe. In the most popular current theory, galaxies in the local Universe are the result of a relatively slow process where small and less massive galaxies merge to gradually build up bigger and more massive galaxies. In this scenario, dubbed "hierarchical merging", the young Universe was populated by small galaxies with little mass, whereas the present Universe contains large, old and massive galaxies - the very last to form in the final stage of a slow assembling process.
If this scenario were true, then one should not be able to find massive elliptical galaxies in the young universe. Or, in other words, due to the finite speed of light, there should be no such massive galaxies very far from us. And indeed, until now no old elliptical galaxy was known beyond a radio-galaxy at redshift 1.55 [3] that was discovered almost ten years ago.
The K20 survey
In order to better understand the formation process of galaxies and to verify if the hierarchical merging scenario is valid, a team of Italian and ESO astronomers [2] used ESO's Very Large Telescope as a "time machine" to do a search for very remote elliptical galaxies. However, this is not trivial. Distant elliptical galaxies, with their content of old and red stars, must be very faint objects indeed at optical wavelengths as the bulk of their light is redshifted into the infrared part of the spectrum. Remote elliptical galaxies are thus among the most difficult observational targets even for the largest telescopes; this is also why the 1.55 redshift record has persisted for so long.
But this challenge did not stop the researchers. They obtained deep optical spectroscopy with the multi-mode FORS2 instrument on the VLT for a sample of 546 faint objects found in a sky area of 52 arcmin2 (or about one tenth of the area of the Full Moon) known as the K20 field, and which partly overlaps with the GOODS-South area. Their perseverance paid off and they were rewarded by the discovery of four old, massive galaxies with redshifts between 1.6 and 1.9. These galaxies are seen when the Universe was only about 25% of its present age of 13,700 million years.
For one of the galaxies, the K20 team benefited also from the database of publicly available spectra in the GOODS-South area taken by the ESO/GOODS team.
A new population of galaxies
The newly discovered galaxies are thus seen when the Universe was about 3,500 million years old, i.e. 10,000 million years ago. But from the spectra taken, it appears that these galaxies contain stars with ages between 1,000 and 2,000 million years. This implies that the galaxies must have formed accordingly earlier, and that they must have essentially completed their assembly at a moment when the Universe was only 1,500 to 2,500 million years old.
The galaxies appear to have masses in excess of one hundred thousand million solar masses and they are therefore of sizes similar to the most massive galaxies in the present-day Universe. Complementary images taken within the GOODS ("The Great Observatories Origins Deep Survey") survey by the Hubble Space Telescope show that these galaxies have structures and shapes more or less identical to those of the present-day massive elliptical galaxies.
The new observations have therefore revealed a new population of very old and massive galaxies.
The existence of such massive and old spheroidal galaxies in the early Universe shows that the assembly of the present-day massive elliptical galaxies started much earlier and was much faster than predicted by the hierarchical merging theory. Says Andrea Cimatti (INAF, Firenze, Italy), leader of the team: "Our new study now raises fundamental questions about our understanding and knowledge of the processes that regulated the genesis and the evolutionary history of the Universe and its structures."
More information
The research presented in this Press Release appears in the July 8 issue of the research journal Nature ("Old galaxies in the young Universe" by A. Cimatti et al.).
The full text of ESO PR 17/04, with two photos and all weblinks, is available at: http://www.eso.org/outreach/press-rel/pr-2004/pr-17-04.html (after expiry of the embargo period).
Notes
[1] This press release is coordinated with the Istituto Nazionale di Astrofisica (INAF). The Italian version is available at www.inaf.it.
[2] The team is composed of Andrea Cimatti (INAF, Firenze), Emanuele Daddi and Alvio Renzini (ESO, Germany), Paolo Cassata, Eros Vanzella and Giulia Rodighiero (Universita di Padova, Italy), Lucia Pozzetti, Marco Mignoli and Giovanni Zamorani (INAF, Bologna), Stefano Cristiani (INAF, Trieste), and Adriano Fontana (INAF, Roma).
[3] In astronomy, the redshift denotes the fraction by which the lines in the spectrum of an object are shifted towards longer wavelengths. The observed redshift of a remote galaxy provides an estimate of its distance.
Contacts
Andrea Cimatti
INAF - Osservatorio Astrofisico di Arcetri
Firenze, Italy
Phone: +39-055-2752-297
Mobile: +39-347-4686338
Email: cimatti@arcetri.astro.it
Alvio Renzini
European Southern Observatory
Garching, Germany
Phone: +49 89 3200 6413
Email: arenzini@eso.org
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Sunspots reaching 1,000-year high Posted: Wednesday, July 7, 2004
By Dr David Whitehouse
BBC News Online science editor
A new analysis shows that the Sun is more active now than it has been at anytime in the previous 1,000 years.
Scientists based at the Institute for Astronomy in Zurich used ice cores from Greenland to construct a picture of our star's activity in the past.
They say that over the last century the number of sunspots rose at the same time that the Earth's climate became steadily warmer.
This trend is being amplified by gases from fossil fuel burning, they argue.
Full Article : news.bbc.co.uk
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Longevity Evolved Late For Humans Posted: Tuesday, July 6, 2004
Old Is Young, Study Finds: Longevity Evolved Late For Humans
Source: University Of Michigan
ANN ARBOR, Mich. -- Researchers at the University of Michigan and the University of California at Riverside have discovered a dramatic increase in human longevity that took place during the early Upper Paleolithic Period, around 30,000 B.C.
In their study of more than 750 fossils to be published July 5 in the Proceedings of the National Academy of Sciences, anthropologists Rachel Caspari and Sang-Hee Lee found a dramatic increase in longevity among modern humans during that time: the number of people surviving to an older age more than quadrupled.
Caspari, an assistant research scientist at the U-M Anthropology Museum, said this increase in the number of relatively old people likely had a major impact, giving modern humans a competitive edge that ensured their evolutionary success.
For the study, the researchers analyzed the ratio of older to younger adults in hominid dental samples from successive time periods: later australopithecines, Early and Middle Pleistocene Homo, Neandertals from Europe and Western Asia and post-Neandertal Early Upper Paleolithic Europeans. They used a new analytical resampling technique allowing them to assess the significance of differences in rates of molar wear.
In the study, they defined "old" to be at least double the age of reproductive maturation, which is also the time when the third molars typically erupt. "While the age of reproductive maturation may have varied in early human groups, if it were 15, then age 30 would be the age at which one could theoretically first become a grandmother," Caspari noted.
Other scientists have argued that the presence of grandmothers confers an important evolutionary advantage since they heavily invest their knowledge and other resources in their reproductive-age daughters and their daughters' offspring.
By calculating the ratio of old-to-young individuals in the samples from each time period, the researchers found a trend of increased survivorship of older adults throughout human evolution. It's not just how long people live that's important for evolution, but the number of people who live to be old, Caspari and Lee pointed out.
The increase in longevity that occurred during the Upper Paleolithic period among modern humans was dramatically larger than the increase identified during earlier periods, they found. "We believe this trend contributed importantly to population expansions and cultural innovations that are associated with modernity," they wrote.
A large number of older people allowed early modern humans to accumulate more information and to transmit specialized knowledge from one generation to another, they speculated. Increased adult survivorship also strengthened social relationships and kinship bonds, as grandparents survived to educate and contribute to extended families and others. Increased survivorship also promoted population growth, the authors explain, since people living longer are likely to have more children themselves, and since they also make major contributions to the reproductive success of their offspring.
"Significant longevity came late in human evolution and its advantages must have compensated somehow for the disabilities and diseases of older age, when gene expressions uncommon in younger adults become more frequent," the authors noted.
"There has been a lot of speculation about what gave modern humans their evolutionary advantage," Caspari said. "This research provides a simple explanation for which there is now concrete evidence: modern humans were older and wiser."
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For more information on the U-M Anthropology Museum, visit: http://www.umma.lsa.umich.edu/
For the Proceedings of the National Academy of Sciences, visit: http://www.pnas.org
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