לוח שנה משולב

The human race has been reading and writing for only 5,000 years, suggesting that the mechanisms for these processes involve both cultural evolution and biological exaptation. Brain mechanisms of reading are hard to discern because skilled reading is so fast and efficient. Use of ambiguous words allows us to slow down some of these processes and explore the interactions of orthographic, phonological, and semantic processes. We took advantage of the characteristics of Hebrew to explore the relative effects of phonological and semantic ambiguity on access to meaning. Twenty-three participants performed a semantic decision talk on pairs of words. Half the pairs were constituted of two unambiguous words, and in half, the first word was either a homophonic homograph (like bank), or a heterophonic homograph (like tear). Our procedure allowed us to separately examine two stages of the access to meaning: the activation of multiple meanings, and then the selection of the appropriate meaning. Previous imaging studies of ambiguity resolution have not made this distinction. In the first stage, we show that different regions of the left hemisphere respond differentially to homophones and to heterophones in both whole brain analysis and in ROI comparisons of sub-regions of both anterior and posterior regions of the left hemisphere. In the second stage, in meaning selection, we again see different effects that are dependent of the phonological status of the ambiguous word, and also similar effects of the interaction between frequency effects and contextual effects in the two hemispheres. We interpret these findings in the context of a brain model of reading.

Viruses and/or virus-like selfish elements are associated with all cellular life forms and are the most abundant biological entities on Earth, with the number of virus particles in many environments exceeding the number of cells by one to two orders of magnitude. The genetic diversity of viruses is commensurately enormous and might substantially exceed the diversity of cellular organisms. Unlike cellular organisms with their uniform replication-expression scheme, viruses possess either RNA or DNA genomes and exploit all conceivable replication-expression strategies. Although viruses extensively exchange genes with their hosts, there exists a set of viral hallmark genes that are shared by extremely diverse groups of viruses to the exclusion of cellular life forms and underlie the cohesiveness and autonomy of the virus world. Multiple evolutionary connections exist between viruses and non-encapsidated selfish genetic elements, such as plasmids and transposons. All these selfish elements intimately interact with cellular hosts, engaged in both cooperation and arms races, and I will argue that this Greater Virus World is a defining factor in the evolution of all life forms.

Giant viruses infecting protists have recently attracted enormous amount of fascinated attention, especially following the discovery of Pandoraviruses with their 2 megabase genomes exceeding in size the genomes of numerous cellular organisms. Speculations have been entertained on the origin of giant viruses (and by inference, possibly, all viruses) from an extinct 4th (and possibly, 5th, 6th etc) domains of cellular life. I will present evidence that the two groups of giant viruses, Pandoraviruses and Mimiviruses, have independently evolved from much smaller viruses via accretion of numerous genes from different sources. These viruses are an integral part of the Virus World not degenerate cells.