The correct term to fill in the blank would be cortisol. In the context of stress hormones and the brain, cortisol has a profound effect on the hippocampus, a brain structure that plays a pivotal role in memory. Cortisol is classified as a steroid hormone which is produced by the adrenal gland. It is deemed as the stress hormone as it is released as a response to stress as part of the fight or flight process. From studies, cortisol was found to have effect on the hippocampus when present in high levels. It damage and kill the cells in that area of the brain. The hippocampus is the area of the brain that is responsible for the long term memory storage. So, when this part is damage then the storage for our memories would surely be affected.
The answer is punctuated equilibrium. This is a theory in evolutionary biology that says the evolution of different species proceeds in a characteristic way of relative stability for very long periods interspersed with shorter periods. During this period new species emerge as others become extinct.
Phospholipids consist of glycerol, phosphate group and two fatty acid chain.
Vestigial organs are organs that we don't use but maybe our ancestor use this organ and the organ will evolve into smaller. Example : Appendix, Hair in chest, canine.
This theory come from J.B Lamarck
