SUMMARY / RELATED TOPICS

Evolutionary developmental biology

Evolutionary developmental biology is a field of biological research that compares the developmental processes of different organisms to infer the ancestral relationships between them and how developmental processes evolved. The field grew from 19th-century beginnings, where embryology faced a mystery: zoologists did not know how embryonic development was controlled at the molecular level. Charles Darwin noted that having similar embryos implied common ancestry, but little progress was made until the 1970s. Recombinant DNA technology at last brought embryology together with molecular genetics. A key early discovery was of homeotic genes; the field is characterised by some key concepts. One is deep homology, the finding that dissimilar organs such as the eyes of insects and cephalopod molluscs, long thought to have evolved separately, are controlled by similar genes such as pax-6, from the evo-devo gene toolkit; these genes are ancient, being conserved among phyla. Another is that species do not differ much in their structural genes, such as those coding for enzymes.

These genes are reused, many times in different parts of the embryo and at different stages of development, forming a complex cascade of control, switching other regulatory genes as well as structural genes on and off in a precise pattern. This multiple pleiotropic reuse explains why these genes are conserved, as any change would have many adverse consequences which natural selection would oppose. New morphological features and new species are produced by variations in the toolkit, either when genes are expressed in a new pattern, or when toolkit genes acquire additional functions. Another possibility is the Neo-Lamarckian theory that epigenetic changes are consolidated at gene level, something that may have been important early in the history of multicellular life. A recapitulation theory of evolutionary development was proposed by Étienne Serres in 1824–26, echoing the 1808 ideas of Johann Friedrich Meckel, they argued that the embryos of'higher' animals went through or recapitulated a series of stages, each of which resembled an animal lower down the great chain of being.

For example, the brain of a human embryo looked first like that of a fish in turn like that of a reptile and mammal before becoming human. The embryologist Karl Ernst von Baer opposed this, arguing in 1828 that there was no linear sequence as in the great chain of being, based on a single body plan, but a process of epigenesis in which structures differentiate. Von Baer instead recognised four distinct animal body plans: radiate, like starfish. Zoologists largely abandoned recapitulation, though Ernst Haeckel revived it in 1866. From the early 19th century through most of the 20th century, embryology faced a mystery. Animals were seen to develop into adults of differing body plan through similar stages, from the egg, but zoologists knew nothing about how embryonic development was controlled at the molecular level, therefore little about how developmental processes had evolved. Charles Darwin argued; as an example of this, Darwin cited in his 1859 book On the Origin of Species the shrimp-like larva of the barnacle, whose sessile adults looked nothing like other arthropods.

Darwin noted Alexander Kowalevsky's finding that the tunicate, was not a mollusc, but in its larval stage had a notochord and pharyngeal slits which developed from the same germ layers as the equivalent structures in vertebrates, should therefore be grouped with them as chordates. 19th century zoology thus converted embryology into an evolutionary science, connecting phylogeny with homologies between the germ layers of embryos. Zoologists including Fritz Müller proposed the use of embryology to discover phylogenetic relationships between taxa. Müller demonstrated that crustaceans shared the Nauplius larva, identifying several parasitic species that had not been recognised as crustaceans. Müller recognised that natural selection must act on larvae, just as it does on adults, giving the lie to recapitulation, which would require larval forms to be shielded from natural selection. Two of Haeckel's other ideas about the evolution of development have fared better than recapitulation: he argued in the 1870s that changes in the timing and changes in the positioning within the body of aspects of embryonic development would drive evolution by changing the shape of a descendant's body compared to an ancestor's.

It took a century. In 1917, D'Arcy Thompson wrote a book on the shapes of animals, showing with simple mathematics how small changes to parameters, such as the angles of a gastropod's spiral shell, can radically alter an animal's form, though he preferred mechanical to evolutionary explanation, but for the next century, without molecular evidence, progress stalled. In the so-called modern synthesis of the early 20th century, Ronald Fisher brought together Darwin's theory of evolution, with its insistence on natural selection and variation, Gregor Mendel's laws of genetics into a coherent structure for evolutionary biology. Biologists assumed that an organism was a straightforward reflection of its component genes: the genes coded for proteins, which built t

Erik Ralske

Erik Ralske is an American classical horn player. He has been principal horn of the Metropolitan Opera Orchestra since 2010, following seventeen seasons as third horn of the New York Philharmonic, he was featured horn soloist of the MET's production of Wagner's Ring Cycle, was a soloist on several occasions with the New York Philharmonic. He is a member of the orchestra's Philharmonic Quintet of New York. Ralske, a native of Long Island, New York, studied at the Juilliard School where he received his Bachelor of Music Degree in 1980 and his Master of Music in 1982. Prior to joining the New York Philharmonic in 1993, he was associate principal of the Houston Symphony as well as principal of the Vancouver Symphony, Florida Symphony, Tulsa Philharmonic. In July 2010 he was offered two principal horn positions in the same week—with the Metropolitan Opera Orchestra and the Los Angeles Philharmonic, he opted to remain in New York and took up his appointment with the Met at the start of the 2010/2011 season.

He has been a member of the faculty at the Juilliard School since 2012 and teaches at Mannes College The New School for Music, the Manhattan School of Music. Ralske's recordings as solo or principal horn include: Moravec: Cool Fire. Naxos Records 8559393 Take 9. MSR Classics 1089 Audra McDonald: Build A Bridge. Nonesuch Records 79862

Collins Bridge

The Collins Bridge was a bridge that crossed Biscayne Bay between Miami and Miami Beach, Florida. At the time it was completed, it was the longest wooden bridge in the world, it was built by farmer and developer John S. Collins with financial assistance from automotive parts and racing pioneer Carl G. Fisher. Fisher, an auto parts magnate, loaned Collins $50,000 in 1911 to complete the bridge when Collins' money ran out. Collins 75 years old, traded Fisher 200 acres of land on Miami Beach for the loan; the 2.5-mile wooden toll bridge opened on June 12, 1913, providing a critical link to the newly established Miami Beach accessible only by a ferry service. The middle of the bridge had a steel lattice truss design, while the ends were wooden, as well as the deck being wooden for the entire length; the original wooden causeway was replaced in 1925 by a series of arch drawbridges and renamed the Venetian Causeway. Historical information