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1 THE EVIDENCE FOR EVOLUTION: DEVELOPMENT AND COMPARATIVE ANATOMY PURPOSE OF THE LECTURE: 1) Explain how the evidence from embryology supports the theory of evolution as descent with modification 2) Look at how changes in development can produce dramatic shifts in morphology – and thus may explain some significant leaps in the evolution of life. 3) Examine some anatomical oddities that are best understood as the result of descent with modification, rather than wise design by a creator. I. EMBRYOLOGY What is the significance of embryology to evolution? If we return to the 4 tenets of Darwin's theory, where do we find it playing a role? In the third statement – "Individuals vary in features…" How is that variation produced? We now know that it is produced by genetic changes – mutations and recombination – but isn't there more to it than that? How are the genetic changes translated into a different shape or size of organism? Are some changes more likely than others? In a very nice book entitled the Shapes of Time, Ken McNamara argues that the role of embryology in evolution has not received the attention it deserves from Neo-Darwinian biologists. Today's evolutionary biologists are often referred to as neo-Darwinian because they accept Darwin's basic ideas but with the added understanding of genetics. McNamara argues that the general view of evolution includes 3 basic elements: 1) genes 2) the results of changes in an organism's developmental patterns (e.g. different size/shape), and 3) natural selection He says that too much emphasis has been placed on 1 and 3 and not enough on 2. To make his point he presents a culinary analogy: genes=chefs, products=food, diners=natural selection. The chefs concoct a dish which is presented to the diners – the diners select what they like and don't like. If they don't like it – it is not made again (goes extinct) – if they do like it, it is replicated. By concentrating most of our research into the genes and natural selection, we have behaved like food critics that discuss only the chefs and the opinions of the diners – and say nothing about what the food is or more important, how it was made. Clearly – we need all 3 bits of information to understand what makes great food – or by analogy to understand the process of evolution.
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2 So consider the process that made you – and the changes that you have gone through since you were first conceived. From zygote to 4 celled blastula to embryo with gill arches and a tail to new born to adult. It is a remarkable transformation that has been regulated and generated by genes. [As an aside, in the 18th century some scientists believed that we come into existence as teeny- tiny versions of our adult selves – and the transformation just involved growth.] This history of your development and growth from zygote to adult is your ONTOGENY. Now if you think about it – your ontogeny did not occur by equal growth of all your parts – some grew more quickly, some more slowly, some
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This note was uploaded on 03/11/2010 for the course GE CLST 70B taught by Professor Morris,m.r./friscia,a.r./moldwin,m.b./vanvalkenburgh,b during the Winter '10 term at UCLA.

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