Friday, December 01, 2006
NASA researchers at Johnson Space Center, Houston have found organic materials that formed in the most distant reaches of the early Solar System preserved in a unique meteorite. The study was performed on the Tagish Lake carbonaceous chondrite, a rare type of meteorite that is rich in organic (carbon-bearing) compounds.
Organic matter in meteorites is a subject of intense interest because this material formed at the dawn of the Solar System and may have seeded the early Earth with the building blocks of life. The Tagish Lake meteorite (info) is especially valuable for this work because much of it was collected immediately after its fall over Canada in 2000 and has been maintained in a frozen state, minimizing terrestrial contamination. The collection and curation of the meteorite samples preserved its pristine state.
In a paper published in the December 1 issue of the journal Science, the team, headed by NASA space scientist Keiko Nakamura-Messenger, reports that the Tagish Lake meteorite contains numerous submicrometer hollow organic globules.
'Similar objects have been reported from several meteorites since the 60's. Some scientists believed these were space organisms, but others thought they were just terrestrial contamination,' said Nakamura-Messenger. The same bubble-like organic globules appeared in this freshest meteorite ever received from space. 'But in the past, there was no way to determine for sure where these organic globules came from because they were simply too small. They are only 1/10,000 inch in size or less.'
Continued at "NASA Scientists Find Primordial Organic Matter in Tagish Lake Meteorite"
Based on the Science paper "Organic Globules in the Tagish Lake Meteorite: Remnants of the Protosolar Disk"
Coordinated transmission electron microscopy and isotopic measurements of organic globules in the Tagish Lake meteorite shows that they have elevated ratios of nitrogen-15 to nitrogen-14 (1.2 to 2 times terrestrial) and of deuterium to hydrogen (2.5 to 9 times terrestrial). These isotopic anomalies are indicative of mass fractionation during chemical reactions at extremely low temperatures (10 to 20 kelvin), characteristic of cold molecular clouds and the outer protosolar disk. The globules probably originated as organic ice coatings on preexisting grains that were photochemically processed into refractory organic matter. The globules resemble cometary carbon, hydrogen, oxygen, and nitrogen (CHON) particles, suggesting that such grains were important constituents of the solar system starting materials.
Technorati: nasa, johnson, space, venter, houston, organic, materials, solar system, unique, meteorite, tagish, lake, carbon, compounds, chondrite, earth, life, building, blocks, canada, contamination, journal, science, nakamura, messenger, globules, meteorites, organisms, electron, microscopy, nitrogen, deuterium, hydrogen, isotopic, anomalies, oxygen
Thursday, November 30, 2006
Oslo, Norway, November 30 (UPI): Breaking News - A Norwegian archaeologist has found what might be the African site of mankind's oldest ritual - a discovery said to change our knowledge of human history.
University of Oslo Associate Professor Sheila Coulson* and colleagues say their discovery in northwest Botswana means Homo sapiens began performing advanced rituals in Africa about 70,000 years ago.
The archaeologists made the discovery while searching for artifacts from the Middle Stone Age in the only hills for hundreds of miles in any direction. The group of small peaks within the Kalahari Desert is known as the Tsodilo Hills and is famous for having the largest concentration of rock paintings in the world.
Original (but short) news report at "Major African archaeological find reported"
UPDATE: A fuller news report can be found here
*Info on Sheila Coulson and the Basarwa Project:
For the past six years Sheila Coulson has been actively involved as an archaeologist in the Collaborative Programme for Basarwa Research; a cooperative venture with the University of Botswana. The aim of this long-term project is to address the position of the indigenous population of Botswana , in this case the Basarwa, also know as the San or Bushman. Continued funding from the Norwegian Universities' Committee for Development Research (NUFU - grant NUFU PRO 20/96) has supported the investigations of researchers from diverse backgrounds in sociology, anthropology, history and archaeology, language and law.
For the archaeologists this program has provided a unique opportunity to work directly with colleagues from the University of Botswana on issues related to the Basarwa, one of the most famous but little known hunter/gatherer groups in the world. The research field area is centred around the Okavango Delta, a vast inland water system located in northern Botswana . Initial archaeological enquiries were linked with the anthropological investigations: these focused on the present Basarwa inhabitants. But in the 2000 and 2001 field seasons the archaeological section shifted their prime area of attention from the dynamic and rapidly changing wetlands of the Okavango Delta to the more stable environment of the outer lying Greater Okavango. The numbers of archaeological sites located due to this change of focus immediately demonstrated the wisdom of this decision. [More] [Europe, Science]
Technorati: oslo, norway, norwegian, archaeologist, african, site, oldest, ritual, discovery, knowledge, human, history, rituals, europe, botswana, homo sapiens, africa, news, university, artifacts, middle, stone age, kalahari, desert, rock, paintings, sheila, coulson, research, basarwa, bushman, san, sociology, anthropology, history, language, law
Chicago, Illinois - It could bite a shark in two. It might have been the first "king of the beasts." And it could teach scientists a lot about humans, because it is in the sister group of all jawed vertebrates.
Dunkleosteus terrelli (info) lived 400 million years ago, grew up to 33 feet long and weighed up to four tons. Scientist have known for years that it was a dominant predator, but new embargoed research to be published in the Royal Society journal Biology Letters on November 29 reveals that the force of this predator's bite was remarkably powerful: 11,000 pounds. The bladed dentition focused the bite force into a small area, the fang tip, at an incredible force of 80,000 pounds per square inch.
Even more surprising is the fact that this fish could also open its mouth very quickly - in just one fiftieth of a second - which created a strong suction force, pulling fast prey into its mouth. Usually a fish has either a powerful bite or a fast bite, but not both.
"The most interesting part of this work for me was discovering that this heavily armored fish was both fast during jaw opening and quite powerful during jaw closing," said Mark Westneat (homepage), Curator of Fishes at The Field Museum and co-author of the paper. "This is possible due to the unique engineering design of its skull and different muscles used for opening and closing. And it made this fish into one of the first true apex predators seen in the vertebrate fossil record." This formidable fish was a placoderms, a diverse group of armored fishes that dominated aquatic ecosystems during the Devonian, from 415 million to 360 million years ago. Dunkleosteus' bladed jaws suggest that it was among the first vertebrates to use rapid mouth opening and a powerful bite to capture and fragment evasive prey prior to ingestion.
Based on "Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator"
(link not working yet:
Placoderms are a diverse group of armoured fishes that dominated the aquatic ecosystems of the Devonian Period, 415-360million years ago. The bladed jaws of predators such as Dunkleosteus suggest that these animals were the first vertebrates to use rapid mouth opening and a powerful bite to capture and fragment evasive prey items prior to ingestion. Here, we develop a biomechanical model of force and motion during feeding in Dunkleosteus terrelli that reveals a highly kinetic skull driven by a unique four-bar linkage mechanism. The linkage system has a high-speed transmission for jaw opening, producing a rapid expansion phase similar to modern fishes that use suction during prey capture. Jaw closing muscles power an extraordinarily strong bite, with an estimated maximal bite force of over 4400N at the jaw tip and more than 5300N at the rear dental plates, for a large individual (6m in total length). This bite force capability is the greatest of all living or fossil fishes and is among the most powerful bites in animals.
Technorati: Dunkleosteus terrelli, chicago, illinois, bite, shark, jawed, vertebrates, dominant, predator, king, beasts, research, royal, society, journal, biology, letters, force, powerful, fish, prey, armored, jaw, fishes, field, museum, skull, ecosystems, devonian, ancient, t. rex, period, ingestion, kinetic, mechanism, coelacanth, fossil, book
Wednesday, November 29, 2006
Scientists have identified a group of genes that control the formation of shapes and colour patterns on the shell of the tropical marine mollusc referred to as 'abalone' (info). A study published in the open access journal BMC Biology reveals that the shape and colour patterns on the shell of the mollusc mirror the localised expression of specific genes in the mantle, a layer of skin situated just below the shell. The authors of the study identify one gene in particular that controls the formation of blue dots on the shell of the mollusc.
Daniel Jackson, Bernard Degnan and colleagues from the University of Queensland, Australia, collaborated with colleagues from the Department of Geobiology at the University of Gottingen, Germany to analyse gene expression in the tropical abalone Haliotis asinina (Images). They sequenced 530 randomly-selected genes expressed in the mantle tissue of the young abalone.
Continued at "Patterns On Tropical Marine Mollusk Shell Mirror Gene Expression Patterns"
Based on the open access BMC Biology paper "A rapidly evolving secretome builds and patterns a sea shell"
Instructions to fabricate mineralized structures with distinct nanoscale architectures, such as seashells and coral and vertebrate skeletons are encoded in the genomes of a wide variety of animals. In mollusks, the mantle is responsible for the extra-cellular production of the shell, directing the ordered biomineralization of CaCO3 and the deposition of architectural and color patterns. The evolutionary origins of the ability to synthesize calcified structures across various metazoan taxa remain obscure, with only a small number of protein families identified from molluskan shells. The recent sequencing of a wide range of metazoan genomes coupled with the analysis of gene expression in non-model animals has allowed us to investigate the evolution and process of biomineralization in gastropod mollusks.
Here we show that over 25% of the genes expressed in the mantle of the vetigastropod Haliotis asinina encode secreted proteins, indicating that hundreds of proteins are likely to be contributing to shell fabrication and patterning. Almost 85% of the secretome encodes novel proteins; remarkably only 19% of these have identifiable homologues in the full genome of the patellogastropod Lottia scutum. The spatial expression profiles of mantle genes that belong to the secretome is restricted to discrete mantle zones, with each zone responsible for the fabrication of one of the structural layers of the shell. Patterned expression of a subset of genes along the length of the mantle is indicative of roles in shell ornamentation. For example, Has-sometsuke maps precisely to pigmentation patterns in the shell, providing the first case of a gene product to be involved in molluskan shell pigmentation. We also describe the expression of 2 novel genes involved in nacre (mother of pearl) deposition.
The unexpected complexity and evolvability of this secretome, and the modular design of the molluskan mantle enables diversification of shell strength and design, and as such must contribute to the variety of adaptive architectures and colors found in mollusk shells. The composition of this novel mantle-specific secretome suggests that there are significant molecular differences in the ways in which gastropods synthesize the shell.
* "The complete article is available as a provisional PDF. The fully formatted PDF and HTML versions are in production."
Technorati: genes, control, formation, shapes, patterns, colour, patterns, shell, tropical, marine, mollusc, study, open access, bmc, biology, mantle, skin, gene, university, queensland, australia, geobiology, gottingen, germany, abolone, tissue, expression, sea, seashells, coral, vertebrate, skeletons, genome, evolutionary, origins, gastropods, complexity
The dinosaurs, along with the majority of all other animal species on Earth, went extinct approximately 65 million years ago. Some scientists have said that the impact of a large meteorite in the Yucatan Peninsula, in what is today Mexico, caused the mass extinction, while others argue that there must have been additional meteorite impacts or other stresses around the same time.
A new study provides compelling evidence that 'one and only one impact' caused the mass extinction, according to a University of Missouri-Columbia researcher.
'The samples we found strongly support the single impact hypothesis,' said Ken MacLeod (homepage), associate professor of geological sciences at MU and lead investigator of the study. 'Our samples come from very complete, expanded sections without deposits related to large, direct effects of the impact - for example, landslides - that can shuffle the record, so we can resolve the sequence of events well. What we see is a unique layer composed of impact-related material precisely at the level of the disappearance of many species of marine plankton that were contemporaries of the youngest dinosaurs. We do not find any sedimentological or geochemical evidence for additional impacts above or below this level, as proposed in multiple impact scenarios.'
MacLeod and his co-investigators studied sediment recovered from the Demerara Rise in the Atlantic Ocean northeast of South America, about 4,500 km (approximately 2,800 miles) from the impact site on the Yucatan Peninsula. Sites closer to and farther from the impact site have been studied, but few intermediary sites such as this have been explored. [Evolution, Dinosaur, Science]
Continued at "New Study Finds that Single Impact Killed Dinosaurs"
Related Geological Society of America Bulletin (GSA) paper:
Impact and extinction in remarkably complete Cretaceous-Tertiary boundary sections from Demerara Rise, tropical western North Atlantic
Kenneth G. MacLeod, Donna I. Whitney, Brian T. Huber, Christian Koeberl
Ocean Drilling Program (ODP) Leg 207, on the Demerara Rise in the western tropical North Atlantic, recovered multiple Cretaceous-Paleogene boundary sections containing an ejecta layer. Sedimentological, geochemical, and paleontological changes across the boundary closely match patterns expected for a mass extinction caused by a single impact. A normally graded, ~2-cm-thick bed of spherules that is interpreted as a primary air-fall deposit of impact ejecta occurs between sediments of the highest Cretaceous Plummerita hantkeninoides foraminiferal zone and the lowest Paleogene P0 foraminiferal zone. There are no other spherule layers in the section. In addition to extinction of Cretaceous taxa, foraminiferal abundance drops from abundant to rare across the boundary. Ir concentrations reach a maximum of ~1.5 ppb at the top of the spherule bed, and the Ir anomaly is associated with enrichment in other siderophile elements. We attribute the unusually well-preserved and relatively simple stratigraphy to the fact that Demerara Rise was close enough (~4500 km) to the Chicxulub impact site to receive ~2 cm of ejecta, yet was far enough away (and perhaps sheltered by the curve of northern South America) to have been relatively unaffected by impact-induced waves.
A recent related post:
A new theory on just what causes Earth's worst mass extinctions may help settle the endless scientific dust-up on the matter. Whether you favor meteor impacts, volcanic eruptions, cosmic rays, epidemics, or some other cause for the worst mass extinction events in Earth's history, no single cause has ever satisfied all scientists all the time for any extinction event. That may be because big extinctions aren't simple events. [More..]
Technorati: dinosaurs, animal, species, earth, extinct, impact, large, meteorite, yucatan, peninsular, mexico, mass extinction, missouri, columbia, macleod, geological, sciences, mu, landslides, record, sediment, demerara, rise, atlantic, ocean, south, america, site, society, odp, cretaceous, taxa, theory, mass, extinctions, dinosaur, evolution, science
Tuesday, November 28, 2006
An international team led by scientists from the United States and New Zealand have observed, for the first time, the bizarre deep-sea communities living around methane seeps off New Zealand's east coast.
'This is the first time cold seeps have been viewed and sampled in the southwest Pacific, and will greatly contribute to our knowledge of these intriguing ecosystems,' says Dr Amy Baco-Taylor (info), from the Woods Hole Oceanographic Institution (WHOI) in Massachusetts, who co-led the voyage with Dr Ashley Rowden (info) from New Zealand's National Institute of Water and Atmospheric Research (NIWA).
The 21-member expedition - led by scientists from WHOI, NIWA, the Scripps Institution of Oceanography, and the University of Hawaii at Manoa (UH) - has spent the last two weeks exploring cold water seeps and other 'chemosynthetic' ecosystems around New Zealand's east coast onboard NIWA's deepwater research vessel Tangaroa.
Cold seeps are areas of the seafloor where methane gas or hydrogen sulphide escapes from large stores deep below. Like hydrothermal vents, cold seeps support unique communities of animals living in symbiosis with microbes that can convert these energy-rich chemicals to living matter (a form of 'chemosynthesis') in the absence of sunlight.
New Zealand is one of the few places in the world where at least four types of chemosynthetic habitats occur in close proximity, allowing scientists to address key questions about the patterns of biological distribution that cannot be addressed elsewhere.
The team visited eight cold seep sites on the continental slope to the east of the North Island, lying at depths of 750 - 1050 m.
'We discovered that one of these sites, "The Builder's Pencil", covers about 180 000 square metres (0.18 square kilometre), making it one of the largest seep sites in the world', says Dr Rowden.
Continued at "Voyage reveals bizarre life around deep-sea gas seeps (Video)"
There are three videos at "Videos of bizarre life around deep-sea gas vents"
Technorati: international, team, united states, new zealand, bizarre, deep-sea, methane, seeps, cold, pacific, knowledge, ecosystems, woods, hole, oceanographic, institute, whoi, massachusetts, national, water, atmospheric, research, niwa, scripps, institution, oceanography, university, hawaii, gas, sulphide, hydrogen, symbiosis, microbes, builders, pencil, video, videos
Scientists from the United Kingdom, France and Italy have studied teeth from Neanderthals (info) with X-rays from the European Synchrotron Radiation Facility (ESRF). They found that the dental development of Neanderthals is very similar to modern humans. Their results are published in the journal Nature this week.
Neanderthals first appeared in Europe approximately 200,000 years ago and became extinct about 25,000 years ago. These predecessors of modern humans have always been considered genetically closer to us than any other members of the genus Homo. It has even been suggested that Neanderthals achieved adulthood faster than modern humans do today.
A research team from the United Kingdom, France and Italy has recently shed new light on this theory by studying this species' teeth. Teeth express genetic differences found between individuals and different populations more efficiently than any other tissues preserved in the fossil record. Studies with teeth can identify a timescale on the entire period of dental development that occurs from before birth until adulthood.
Continued at "Synchrotron Reveals How Neanderthal Teeth Grew"
Based on the Letter to Nature "How Neanderthal molar teeth grew" by Macchiarelli* et al.
Growth and development are both fundamental components of demographic structure and life history strategy. Together with information about developmental timing they ultimately contribute to a better understanding of Neanderthal extinction. Primate molar tooth development tracks the pace of life history evolution most closely and tooth histology reveals a record of birth as well as the timing of crown and root growth. High-resolution micro-computed tomography now allows us to image complex structures and uncover subtle differences in adult tooth morphology that are determined early in embryonic development. Here we show that the timing of molar crown and root completion in Neanderthals matches those known for modern humans but that a more complex enamel-dentine junction morphology and a late peak in root extension rate sets them apart. Previous predictions about Neanderthal growth, based only on anterior tooth surfaces were necessarily speculative. These data are the first on internal molar microstructure; they firmly place key Neanderthal life history variables within those known for modern humans.
*See the Nature interview "Roberto Macchiarelli: The whole tooth" (25 September 2003):
Roberto Macchiarelli is a palaeoanthropologist. Until recently at the National Museum of Prehistory and Ethnography in Rome, he is currently professor of human palaeontology at the University of Poitiers, France.
What was your first experiment as a child?
I grew a colony of bacteria. I remember my father's embarrassed expression as he asked fruitlessly for agar-agar in all the pharmacies of the district.
Whose graduate student would you most like to have been?
Albert Dahlberg at the anthropology department of the University of Chicago in the early 1970s.
What scientific paper changed your career path?
Loring Brace's papers on dental size reduction in hominid evolution... [More]
Image Credits: Luca Bondiolli and Arnaud Mazurier.
Technorati: united kingdom, france, italy, teeth, neanderthals, x-rays, european, synchroton, radiation, facility, esrf, dental, modern, humans, journal, nature, europe, extinct, genus, research, theory, teeth, genetic, fossil, record, neanderthal, history, extinction, primate, molar, teeth, histology, morphology, enamel, dentine, life, books, rome
Monday, November 27, 2006
Science teaching materials deemed 'not appropriate' by the government should be allowed in class, Education Secretary Alan Johnson has been urged.
Chemistry teacher at Liverpool's Blue Coat School, Nick Cowan, says the packs promoting intelligent design are useful in debating Darwinist evolution.
Education officials insist intelligent design is not recognised as science.
It argues that evolution cannot explain some things so the universe must have had an intelligent creator.
The packs were sent out to 5,000 secondary schools by a group of academics and clerics known as Truth in Science.
The Department for Education and Skills said they were inappropriate and not supportive of the science curriculum.
Continued at "Let us test Darwin, teacher says"
See last week's (Monday, November 20, 2006) "Government department rejects creationist infiltration of science teaching" post:
"The Christian think-tank Ekklesia and the British Humanist Association (BHA) have welcomed a statement from the British government's Department for Education and Skills (DfES) clarifying that 'creationism' - an ideology which uses discredited readings of scriptural texts to deny fundamental scientific discoveries - can have no legitimate place in UK school science classrooms.
The issue arose after a creationist group calling itself Truth in Science, the majority of whose key supporters believe that the world is only 8-10,000 years old, sent out a pack to secondary science heads encouraging them to include creationism and its cousin 'intelligent design' in their teaching.
Ekklesia and the BHA teamed up to emphasise that this is not an issue which should divide religious and non-religious people. They wrote together to the Department for Education and Skills on 29 September 2006, asking for clear guidelines."
Technorati: science, teaching, government, class, education, secretary, alan, johnson, chemistry, teacher, liverpool, blue, coat, school, intelligent design, darwinist, evolution, universe, creator, academics, clerics, truth, curriculum, darwin, ekklesia, bha, creationism, ideology, uk, secondary, schools, religious, introduction, eugenie, c, scott
Sunday, November 26, 2006
The evolution of intelligence, and why our brains have shrunk
They say nice guys finish last, and according to a new model that attempts to understand why humans evolved distinctively large brains, that was never more true than 100,000 years ago.
Scientists have called humans the "uniquely unique species" due in large part to the size of our brains in relation to our bodies and our complex social interactions.
What science has had trouble explaining is why, 100,000 years ago, over a relatively short period in biological evolution, we developed such large brains at a time when the functions made possible by a large brain would seem unnecessary.
Gavrilets, a professor of ecology and evolutionary biology and mathematics, developed a mathematical model to test the theory that humans' large brains are a result of the most clever males using increasingly sophisticated strategies to outmaneuver other males in the quest to reproduce as much as possible.
Some evolutionary biologists have theorized about the idea of Machiavellian intelligence - namely, that there is a distinct advantage to the types of trickery and deception espoused by the 14th century Italian noble Niccolo Machiavelli in his pamphlet entitled "The Prince." They theorize that the advantage is seen most strongly in the task of reproduction.
"Mating success is a powerful determinant in genetic selection," said Gavrilets. "This research indicates that the most successful males were those who beat out other males in their quest to reproduce."
A somewhat more modern example of this concept is Genghis Khan. The 12th century warrior, famed for building the largest empire in world history and for his unusually high amount of reproductive activity, left a striking genetic mark on the Eastern world that can still be seen today. Eight percent of all Asian males carry a chromosome which appears to be directly linked to Genghis Khan, said Gavrilets.
Gavrilets admits that his results do not reflect the moral values shown by modern humans, and that they could be seen as controversial.
"The idea of competition for reproductive success as the main driver of our evolutionary leap is not what you would call politically correct," said Gavrilets.
In fact, the results of Gavrilets' mathematical model show that after a burst of growth in brain size resulting from a spike in Machiavellian intelligence, there should be a leveling off of both Machiavellian behavior and brain size, apparently corresponding to our current stage of development.
The model, developed with the help of UT computer science undergraduate Aaron Vose, looks at genetic factors in the increase of brain size as well as society's influence through the spread of "memes." They define a meme as an idea or strategy that can be learned from other members of the group and that can be used to subvert others as people look to gain social power.
Vose and Gavrilets used powerful computer clusters to test their model over thousands of "generations" of humans, and found that the evolution of brain size happened in three stages.
First, there is an extended waiting period during which there is little sign of the evolution to come; second, a "cerebral explosion" during which the learning ability, brain size, number of memes and overall Machiavellian fitness grow very rapidly; and finally, a saturation phase in which these qualities cease to grow and in some cases slightly decline.
Gavrilets notes that his research does not advocate for Machiavellian behavior as a way for humans to further evolve.
"It is important to point out that there's a difference between how you acquire a tool like a large brain, and how you use it once you have it," said Gavrilets.
Source (adapted): University of Tennessee PR "UT Researcher Creates 'Machiavellian' Model of Evolution of Human Intelligence" October 31 2006
 Based on the Proceedings of the National Academy of Sciences paper:
The dynamics of Machiavellian intelligence
Sergey Gavrilets, and Aaron Vose
Published online before print October 30, 2006, 10.1073/pnas.0601428103
PNAS | November 7, 2006 | vol. 103 | no. 45 | 16823-16828
The "Machiavellian intelligence" hypothesis (or the "social brain" hypothesis) posits that large brains and distinctive cognitive abilities of humans have evolved via intense social competition in which social competitors developed increasingly sophisticated "Machiavellian" strategies as a means to achieve higher social and reproductive success. Here we build a mathematical model aiming to explore this hypothesis. In the model, genes control brains which invent and learn strategies (memes) which are used by males to gain advantage in competition for mates. We show that the dynamics of intelligence has three distinct phases. During the dormant phase only newly invented memes are present in the population. During the cognitive explosion phase the population's meme count and the learning ability, cerebral capacity (controlling the number of different memes that the brain can learn and use), and Machiavellian fitness of individuals increase in a runaway fashion. During the saturation phase natural selection resulting from the costs of having large brains checks further increases in cognitive abilities. Overall, our results suggest that the mechanisms underlying the "Machiavellian intelligence" hypothesis can indeed result in the evolution of significant cognitive abilities on the time scale of 10 to 20 thousand generations. We show that cerebral capacity evolves faster and to a larger degree than learning ability. Our model suggests that there may be a tendency toward a reduction in cognitive abilities (driven by the costs of having a large brain) as the reproductive advantage of having a large brain decreases and the exposure to memes increases in modern societies.