Darwin s view of life contrasted sharply with the conventional paradigm of an Earth only a few thousand years old, populated by unchanging forms of life that had been individually made during the single week in which the Creator formed the entire universe. Darwin s book challenged a worldview that had been taught for centuries. But these slight variations between individuals in a population are the variations Darwin wrote most about as the raw material for natural selection. February 15 5a. Individuals with genes promoting the storage of high-energy molecules during feasts may have been those that survived famines.
Most animals eat other organisms, dead or alive, whole by piece.
In addition to being very long, the alimentary canals of many herbivorous vertebrates have special fermentation chambers where symbiotic bacteria and protists live. These microorganisms have enzymes that can digest cellulose, which the animal itself cannot digest. March 1 6a. The immune system exhibits the critical feature of self-tolerance . Failure of self-tolerance can lead to autoimmune diseases such as multiple sclerosis.