Dawkins explains that DNA must be thought of as the most sophisticated information system imaginable: 'Life is just bytes and bytes of information,' he writes. Using this perspective, he describes the mechanisms by which evolution has taken place, gradually but inexorably, over a period of three thousand million years.
It is the story of how evolution happens, rather than a narrative of what has actually happened in evolution. He discusses current views on the process of human evolution, including the idea that we all trace back to a comparatively recent African 'Eve', and speculates that the 'information explosion' that was unleashed on Earth when DNA came into being has almost certainly happened in other places in the universe.
A Devil's Chaplain: Selected Writings. Dawkins has an enviable gift. Richard Dawkins is an evolutionary biologist renowned throughout the world. He was educated at Oxford and taught zoology before becoming the first holder of the Charles Simonyi Chair of the Public Understanding of Science at Oxford University, in His previous books rank among the most influential intellectual works of our time.
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The making of a metaphor
Price : Add me. Luke Hohmann Innovation Games Price In a world where most organisms die before they can procreate, descendants are common but ancestors are rare.
But we can all claim an unbroken chain of successful ancestors, right back to the first single-celled organism. If the success of an organism is measured by its ability to survive and reproduce, then all living organisms can be said to have inherited "good genes " from successful ancestors. Each generation of organisms is a sieve against which replicated and mutated genes are tested. Good genes fall through the sieve into the next generation while bad genes are removed. This explains why organisms become better and better at whatever it takes to succeed, and is in stark contrast to Lamarckism , which would require successful organisms to refine their genes during their lifetime.
Following this gene-centered view of evolution , it can be argued that an organism is no more than a temporary body in which a set of companion genes actually alleles co-operate toward a common goal: to grow the organism into adulthood, before they go their separate ways in bodies of the organism's progeny. Bodies are created and discarded, but good genes live on as replicas of themselves, a result of a high-fidelity copy process typical of digital encoding.
River Out Of Eden: A Darwinian View Of Life (Science Masters Series)
Through meiosis sexual reproduction , genes share bodies with different companion genes in successive generations. Thus genes can be said to flow in a river through geological time. Even though genes are selfish , over the long run every gene needs to be compatible with all other genes in the gene pool of a population of organisms, to produce successful organisms. A river of genes may fork, mostly due to the geographical separation between two populations of organisms.
Because genes in the two branches never share the same bodies, they may drift apart until genes from the two branches become incompatible. Organisms created by these two branches form separate, non- interbreeding species , completing the process of speciation. When tracing human lineage back in time, most people look at parents, grandparents, great-grandparents and so on.
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The same approach is often taken when tracing descendants via children and grandchildren. Dawkins shows that this approach is misguided, as the numbers of ancestors and descendants seem to grow exponentially as generations are added to the lineage tree. In just 80 generations, the number of ancestors can exceed a trillion trillion.
River Out of Eden: A Darwinian View of Life - Richard Dawkins - Google книги
This simple calculation does not take into account the fact that every marriage is really a marriage between distant cousins which include second cousins, fourth cousins, sixteenth cousins and so on. The ancestry tree is not really a tree , but a graph. Dawkins prefers to model ancestry in terms of genes flowing through a river of time. An ancestor gene flows down the river either as perfect replicas of itself or as slightly mutated descendant genes.
Dawkins fails to explicitly contrast ancestor organism and descendant organisms against ancestor genes and descendant genes in this chapter. But the first half of the chapter is really about differences between these two models of lineage. While organisms have ancestry graphs and progeny graphs via sexual reproduction , a gene has a single chain of ancestors and a tree of descendants.
Given any gene in the body of an organism, we can trace a single chain of ancestor organisms back in time, following the lineage of this one gene, as stated in the coalescent theory. Because a typical organism is built from tens of thousands of genes, there are numerous ways to trace the ancestry of organisms using this mechanism. But all these inheritance pathways share one common feature. If we start with all humans alive in and trace their ancestry by one particular gene actually a locus , we find that the farther we move back in time, the smaller the number of ancestors become.
The pool of ancestors continues to shrink until we find the most recent common ancestor MRCA of all humans alive in via this particular gene pathway.
tellibacheti.tk In theory, one can also trace human ancestry via a single chromosome, as a chromosome contains a set of genes and is passed down from parents to children via independent assortment from only one of the two parents. But genetic recombination chromosomal crossover mixes genes from non-sister chromatids from both parents during meiosis , thus muddling the ancestry path.
Mitochondrial DNA, therefore, can be used to trace matrilineal inheritance and to find the Mitochondrial Eve also known as the African Eve , the most recent common ancestor of all humans via the mitochondrial DNA pathway. The main themes of the third chapter are borrowed from Dawkins' own book, The Blind Watchmaker. This chapter shows how the gradual, continuous and cumulative enhancement to organisms via natural selection is the only mechanism which can explain the complexity we observe all around us in nature.
Dawkins adamantly refutes the "I cannot believe so and so could have evolved by natural selection" argument of Creationists , calling it the Argument from Personal Incredulity.
Creationists often claim that some features of organisms e. Some say, "half of an X will not work at all.
Do you actually know the first thing about orchids, or wasps, or the eyes with which wasps look at females and orchids? What emboldens you to assert that wasps are so hard to fool that the orchid's resemblance would have to be perfect in all dimensions in order to work? Dawkins goes on to illustrate his point by demonstrating how scientists have been able to fool creatures big and small using seemingly dumb triggers. For instance, stickleback fish treat a pear-shape as a sex bomb a supernormal stimulus.