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Posts Tagged ‘evolution’

Big brains arose twice in higher primates

After taking a fresh look at an old fossil, John Flynn, Frick Curator of Paleontology at the American Museum of Natural History, and colleagues determined that the brains of the ancestors of modern Neotropical primates were as small as those of their early fossil simian counterparts in the Old World. This means one of the hallmarks of primate biology, increased brain size, arose independently in isolated groups—the platyrrhines of the Americas and the catarrhines of Africa and Eurasia.

“Primatologists have long suspected that increased encephalization may have arisen at different points in the primate evolutionary tree, but this is the first clear demonstration of independent brain size increase in New and Old World anthropoids,” says Flynn of the paper that appeared in the Museum’s publication Novitates this June. Encephalization is the increase in brain size relative to body size. Animals with large encephalization quotients (E.Q.’s) are those with bigger brains relative to their body size in comparison to the average for an entire group. Most primates and dolphins have high E.Q.’s relative to other mammals, although some primates (especially apes and humans) have higher E.Q.’s than others. … Continue Reading »

Closing the gap between fish and land animals

New exquisitely preserved fossils from Latvia cast light on a key event in our own evolutionary history, when our ancestors left the water and ventured onto land. Swedish researchers Per Ahlberg and Henning Blom from Uppsala University have reconstructed parts of the animal and explain the transformation in the new issue of Nature.

It has long been known that the first backboned land animals or “tetrapods” – the ancestors of amphibians, reptiles, birds and mammals, including ourselves – evolved from a group of fishes about 370 million years ago during the Devonian period. However, even though scientists had discovered fossils of tetrapod-like fishes and fish-like tetrapods from this period, these were still rather different from each other and did not give a complete picture of the intermediate steps in the transition.

In 2006 the situation changed dramatically with the discovery of an almost perfectly intermediate fish-tetrapod, Tiktaalik, but even so a gap remained between this animal and the earliest true tetrapods (animals with limbs rather than paired fins). Now, new fossils of the extremely primitive tetrapod Ventastega from the Devonian of Latvia cast light on this key phase of the transition.

“Ventastega was first described from fragmentary material in 1994; since then, excavations have produced lots of new superbly preserved fossils, allowing us to reconstruct the whole head, shoulder girdle and part of the pelvis”, says Professor Per Ahlberg at the Department of Physiology and Developmental Biology, Uppsala University.

The recontructions made by Professor Ahlberg and Assistant Professor Henning Blom together with British and Latvian colleagues show that Ventastega was more fish-like than any of its contemporaries, such as Acanthostega. The shape of its skull, and the pattern of teeth in its jaws, are neatly intermediate between those of Tiktaalik and Acanthostega.

“However, the shoulder girdle and pelvis are almost identical to those of Acanthostega, and the shoulder girdle is quite different from that of Tiktaalik (the pelvis of Tiktaalik is unknown), suggesting that the transformation from paired fins to limbs had already occurred. It appears that different parts of the body evolved at different speeds during the transition from water to land”, says Per Ahlberg.

Source: Uppsala University

Ventastega curonica and the origin of tetrapod morphology. Per E. Ahlberg, Jennifer A. Clack, Ervi macrns Luks caronevic carons, Henning Blom & Ivars Zupincedils caron. Nature Volume 453 Number 7199. doi:10.1038/nature06991

Josh says:

It’s too bad DNA doesn’t really get preserved in fossils. While reading this type of thing though, I can’t help but think how this is just another nail in the coffin for the creationists, such when a new “species” of E. coli recently evolved in the lab. However, even in light of such strong evidence, they still just call it fraudulant, even to the author’s face.

New discovery proves ‘selfish gene’ exists

A new discovery by a scientist from The University of Western Ontario provides conclusive evidence which supports decades-old evolutionary doctrines long accepted as fact.

Since renowned British biologist Richard Dawkins (“The God Delusion”) introduced the concept of the ‘selfish gene’ in 1976, scientists the world over have hailed the theory as a natural extension to the work of Charles Darwin.

In studying genomes, the word ‘selfish’ does not refer to the human-describing adjective of self-centered behavior but rather to the blind tendency of genes wanting to continue their existence into the next generation. Ironically, this ‘selfish’ tendency can appear anything but selfish when the gene does move ahead for selfless and even self-sacrificing reasons.

For instance, in the honey bee colony, a complex social breeding system described as a ‘super-organism,’ the female worker bees are sterile. The adult queen bee, selected and developed by the worker bees, is left to mate with the male drones.

Because the ‘selfish’ gene controlling worker sterility has never been isolated by scientists, the understanding of how reproductive altruism can evolve has been entirely theoretical – until now.

Working with Peter Oxley of the University of Sydney in Australia, Western biology professor Graham Thompson has, for the first time-ever, isolated a region on the honey bee genome that houses this ‘selfish’ gene in female workers bees.

This means that the ‘selfish’ gene does exist, not just in theory but in reality. “We don’t know exactly which gene it is, but we’re getting close.”

“This basically provides a validation for a huge body of socio-biology,” says Thompson, who adds the completion of Honey Bee Genome Project in 2006 was crucial to this discovery.

Source: University of Western Ontario

Researchers find an evolutionarily preserved signature in the primate brain

Researchers from Uppsala University, Karolinska Institute, and the University of Chicago, have determined that there are hundreds of biological differences between the sexes when it comes to gene expression in the cerebral cortex of humans and other primates. These findings, published June 20th in the open-access journal PLoS Genetics, indicate that some of these differences arose a very long time ago and have been preserved through the evolution of primates. These conserved differences constitute a signature of sex differences in the brain.

More obvious gender differences have been preserved throughout primate evolution; examples include average body size and weight, and genitalia design. This novel study focuses on gene expression within the cerebral cortex – that area of the brain that is involved in such complex functions in humans and other primates as memory, attentiveness, thought processes, and language.

The researchers measured gene expression in the brains of male and female primates from three species: humans, macaques, and marmosets. To measure activity of specific genes, the products of genes (RNA) obtained from the brain of each animal were hybridized to microarrays containing thousands of DNA clones coding for thousands of genes. The authors also investigated DNA sequence differences among primates for genes showing different levels of expression between the sexes.

“Knowledge about gender differences is important for many reasons. For example, this information may be used in the future to calculate medical dosages, as well as for other treatments of diseases or damage to the brain,” says Professor Elena Jazin of Uppsala University.

Lead author Björn Reinius notes that the study does not determine whether these differences in gene expression are in any way functionally significant. Such questions remain to be answered by future studies.

Source: Public Library of Science

Reinius B, Saetre P, Leonard JA, Blekhman R, Merino-Martinez R, et al. (2008) An Evolutionarily Conserved Sexual Signature in the Primate Brain. PLoS Genet 4(6): e1000100. doi:10.1371/journal.pgen.1000100

Josh says:

I’d be curious to see how these differences compare to the expression levels in homosexual males and females.

Genetic mutations in human brain linked to walking on all 4s

What are the genes implicated in upright walking of humans? The discovery of four families in which some members only walk on all fours (quadrupedality) may help us understand how humans, unlike other primates, are able to walk for long periods on only two legs, a scientist will tell the annual conference of the European Society of Human Genetics tomorrow (Monday 2 June).

The quadrupedal families in Turkey previously attracted attention in 2005, when they were discovered. Now the Turkish team reports that they have found the first gene implicated in quadrupedal locomotion in these families.

Professor Tayfun Ozcelik, of Bilkent University, Ankara, Turkey, and colleagues, studied four unrelated families where some members were affected by the rare quadrupedic condition, Unertan syndrome, which is also associated with imperfect articulation of speech, mental retardation, and defects in the cerebellum, a part of the brain involved in motor control. They found that the affected individuals in two families had mutations in the gene responsible for the expression of very low density lipoprotein receptor (VLDLR), a protein which is known to be critical to the proper functioning of the cerebellum during development.

Although the families lived in isolated villages 200-300 km apart and reported no ancestral relationships, the scientists expected to find a single genetic mutation implicated in the condition. They were surprised to find that this was not the case.

“We carried out genome-wide screening on these families”, said Professor Ozcelik, “and found regions of DNA that were shared by all those family members who walk on all fours. However, we were surprised to find that genes on three different chromosomes are responsible for the condition in four different families.

“In families A and D there were mutations in VLDLR on chromosome 9, and in family B the phenotype maps to chromosome 17 to a region that contains at least 157 genes, and we are still looking for the precise mutation. Neither region appears to be implicated for family C.”

In all cases, the affected individuals were the offspring of consanguineous marriages, which suggests that if they had married outside the family they would not have had the condition. All of them had significant developmental delay in infancy. “Whereas normal infants make the transition to walking on two legs in a relatively short period”, said Professor Ozcelik, “these individuals continued to move on their palms and feet and never walked upright. Although they can stand from a sitting position and maintain this upright position with flexed hips and knees, they virtually never initiate bipedal walking on their own.”

It has been suggested in the past that lack of access to medical care exacerbated the effects of an under-developed cerebellum, and that this led to quadrupedality. “Although it may be true that family B lacked proper medical care, families A and D had consistent access to good medical attention, and both families sought a correction of quadrupedality in their affected children”, said Professor Ozcelik. “Indeed, an unaffected member of family A is a physician, who has been actively involved in the medical interventions. In addition, the parents in family A also discouraged their affected children from walking on all fours, to no avail. We think that social factors are unlikely to be involved in the development of quadrupedal locomotion.”

Mutations causing VLDLR deficiency are also found in Hutterites, a group of Anabaptists who live in colonies of North America. There, however, most of the affected individuals cannot walk at all. The neurological characteristics of the affected members of the Turkish families and the Hutterites seem similar, with the most striking difference being that the Turkish individuals are able to walk on all fours, said the scientists. They hypothesize that the Hutterites may be more profoundly affected due to the deficiency in VLDLR and a neighbouring gene, and therefore lack the motor skills even for quadrupedal locomotion.

Along with brain enlargement, speech, and the ability to make tools, upright walking has long been regarded as one of the key traits that have led to modern humans. Professor Ozcelik’s team have opened a window on how mutations in VLDLR affect brain development and influence gait in humans.

“It will be interesting to see if the VLDLR gene is involved in other types of cerebellar ataxias. In addition, we hope to identify the defective genes associated with quadrupedal locomotion in families B and C”, he says.

Source: European Society of Human Genetics

Josh says:

While not really practical immediately, it’s an interesting study. I think the title and content are a bit misleading, as there are mutations that disrupt neurological development and a side effect of some of these is quadrupedality. It would almost seem to me that perhaps the brain reverts to a more “primitive” setup and just defaulted to quadrupedality.

Andrew says:

I think that this is misleading, too, so I changed the title a bit. (original title was “genetic mutation linked to walking on all 4s,” which implied some “missing link” gene.

The mutations are various flaws in a lipoprotein receptor which impairs cerebellum development, not all the complex skeletal, muscular, and neurological mutations (and more) plausibly necessary to produce a viable quadruped human. The link-bait here is the “mutation of the missing link,” and that’s an irritating and fundamental misunderstanding about how evolution works that doesn’t need to be perpetuated here.

But what I do think is significant is that this suggests that an advanced cerebellum evolved first, and then the relevant skeletal-muscular changes gradually accumulated to make modern bipedal humans from an already somewhat transitory bipedal/quadrupedal evolutionary state (like primates). Mutations which favor bipedality at the expense of quadrupedality are only an evolutionary advantage once the brain can process the locomotion, something that an advanced cerebellum apparently can do. But, an advanced cerebellum is probably a net advantage (or at least, not a disadvantage) before bipedality. This supports contemporary evolutionary theory.

Clues to ancestral origin of placenta emerge in Stanford study

Researchers at the Stanford University School of Medicine have uncovered the first clues about the ancient origins of a mother’s intricate lifeline to her unborn baby, the placenta, which delivers oxygen and nutrients critical to the baby’s health.

The evidence suggests the placenta of humans and other mammals evolved from the much simpler tissue that attached to the inside of eggshells and enabled the embryos of our distant ancestors, the birds and reptiles, to get oxygen. … Continue Reading »

Evolution on the table top

Evolution has taken another step away from being dismissed as “a theory” in the classroom, thanks to a new paper published this week in the online open-access journal PLoS Biology. The research article, by Brian Paegel and Gerald Joyce of The Scripps Research Institute, California, documents the automation of evolution: they have produced a computer-controlled system that can drive the evolution of improved RNA enzymes—biological catalysts—without human input. In the future, this “evolution-machine” could feature in the classroom as well as the lab, allowing students to watch evolution happen in their biology lessons.

The evolution of molecules via scientific experiment is not new. The first RNA enzymes to be “evolved” in the lab were generated in the 1990s. But what is exciting about this work is that the process has been made automatic. Thus evolution is directed by a machine without requiring human intervention-other then providing the initial ingredients and switching the machine on. … Continue Reading »

International team of scientists discover clue to delay of life on Earth

Scientists from around the world have reconstructed changes in Earth’s ancient ocean chemistry during a broad sweep of geological time, from about 2.5 to 0.5 billion years ago. They have discovered that a deficiency of oxygen and the heavy metal molybdenum in the ancient deep ocean may have delayed the evolution of animal life on Earth for nearly 2 billion years.

The findings, which appear in the March 27 issue of Nature, come as no surprise to Ariel Anbar, one of the authors of the study and an associate professor at Arizona State University with joint appointments in the Department of Chemistry and Biochemistry and the School of Earth and Space Exploration in the College of Liberal Arts and Sciences. The study was led by Clint Scott, a graduate student at University of California Riverside. Scott works with Timothy Lyons, a professor of biogeochemistry at UCR who is a long-time collaborator of Anbar’s and also an author of the paper. … Continue Reading »