Mammalian Brain Development

 

The embryonic fetal brains of all mammals develop in the same way. In humans and many other mammals, new neurons are created mainly before birth, and the infant brain contains more neurons than the adult brain. This is mentioned in the book as Neural Darwinism, the strongest neurons survive ans the weak deteriorate and die. There are, however, a few areas where new neurons continue to be generated throughout life. The two areas that are well established are the olfactory bulb, which is involved in the sense of smell, research shows that one of the first signs of mammalian brain evolution begun with the sense of smell, and the dentate gyrus of the hippocampus where there is evidence that the new neurons play a role in storing newly acquired memories. With these exceptions, however, the set of neurons that is present in early childhood is the set that is present for life. Glial cells are different: as with most types of cells in the body, they are generated throughout the lifespan. 

     All vertebrate brains share a common underlying form, which appears most clearly during early stages of embryonic development. In its earliest form, the brain appears as three swellings at the front end of the neural tube; these swellings eventually become the forebrain, midbrain, and hindbrain (the prosencephalon, mesencephalon, and rhombencephalon, respectively). At the earliest stages of brain development, the three areas are roughly equal in size. In many classes of vertebrates, such as fish and amphibians, the three parts remain similar in size in the adult, but in mammals the forebrain becomes much larger than the other parts, and the midbrain becomes very small.

    

     ^{Normally brain is compared in terms of its size. The larger the brain is compared to its body mass the higher the mental faculties of that animal is. However that is not the case in all species therefore it is not a very valid equation.}

     ^{Although the same basic components are present in all vertebrate brains, some branches of vertebrate evolution have led to substantial distortions of brain geometry, especially in the forebrain area. These distortions can make it difficult to match brain components from one species with those of another species.}

     ^{On a different note concerning brain size, research done on 500 different types of mammal species throughout their lifespan showed a correlation with brain size and their longevity. The article basically says that the larger the body brain size ration the longer the lifespan.}