Human Evolutionary and Prenatal Development

Abstract

“We are what we are because of history, both our ancestors’ history and the history of our own lives” (Carlson, 1984, p. 6). This is another way of saying that our phenotype (physical appearance and behavior) is determined jointly by characteristics that we inherit from our ancestors (phylogeny) and from our unique individual histories (ontogeny). We can trace the beginning of each individual’s history to conception, when a single sperm fertilizes an ovum. At that precise moment, the fertilized ovum contains all the genetic information needed to form an adult human being, given extensive environmental influences. This “genetic heritage” represents the accumulation of approximately 3.5 billion of years of evolution by natural selection. This chapter overviews some important phylogenetic developments related to the evolution of the human species (Homo sapiens), including how humans are similar to other mammals and more specifically the primates to whom we are closely related. Then it describes the ontogenetic developmental changes that begin to occur from conception through birth.