Summary Of Chapter 8 And 9 Of Your Inner Fish

Throughout chapters 8 and 9 of Your Inner Fish, Neil Shubin discusses the relationship between humans and other organisms, specifically the connection regarding the sense of smell and vision. Fossils and the geological record are powerful sources of evidence about the past. By extracting DNA from a tissue of varying species, the history of any part of the body, such as smelling, can be deciphered. Similar to fish, amphibians, reptiles, mammals, and birds, the human’s sense of smell is housed in the skull. Like the other animals, there are one or more holes through which air is brought inside and a set of specialized tissues where chemicals in the air can interact with neurons. The arrangement of holes, spaces, and membranes from fish to man

Primitive fish, like lampreys and hagfish, have receptors that combine both water genes and air genes. This clearly shows that these primitive fish arose before the smelling genes split into two types. The number of odor genes have increased over time, from relatively few in jawless fish to the enormous number seen in mammals. The extra genes in mammals are all variations of the genes found in jawless fish. Therefore, the large number of odor genes in mammals arose by many rounds of duplication of the small number of genes in primitive organisms. Additionally, mutations knock out the function of specific genes, but they remain present in the DNA as silent records of evolution. Hundreds of human olfactory genes are left over from mammal ancestors who relied more heavily on smell to

There is a stunning variety of photoreceptor organs, but every animal uses the same kind of light-capturing molecule called an opsin. Insects, humans, and clams all use opsins and the history of human eyes can be traced through differences in the structure of these molecules. The structure of opsins is similar to parts of certain molecules in bacteria. The precise molecular similarities in this molecule suggest a shared history with bacteria. Modified pieces of ancient bacteria lie inside human retinas, helping people to see. Two human receptor-making genes are similar to those in other mammals. This implies that human color vision began when one of the genes in other mammals duplicated and copies specialized over time for different light sources. The switch to color vision correlates to a switch from a monochromatic forest to one with a multitude of colors in