<Tr> <Td> <Ul> <Li> Human embryogenesis </Li> <Li> Fetus </Li> <Li> Infant </Li> <Li> Toddler </Li> <Li> Early childhood </Li> <Li> Child </Li> <Li> Preadolescence </Li> <Li> Adolescence </Li> <Li> Adult </Li> <Li> Middle age </Li> <Li> Old age </Li> </Ul> </Td> </Tr> <Ul> <Li> Human embryogenesis </Li> <Li> Fetus </Li> <Li> Infant </Li> <Li> Toddler </Li> <Li> Early childhood </Li> <Li> Child </Li> <Li> Preadolescence </Li> <Li> Adolescence </Li> <Li> Adult </Li> <Li> Middle age </Li> <Li> Old age </Li> </Ul> <Tr> <Th> Biological milestones </Th> </Tr> <Tr> <Td> <Ul> <Li> Fertilization </Li> <Li> Childbirth </Li> <Li> Walking </Li> <Li> Language acquisition </Li> <Li> Puberty </Li> <Li> Menopause </Li> <Li> Ageing </Li> <Li> Death </Li> </Ul> </Td> </Tr>

According to the text in the u.s. today the period of middle adulthood spans the ages from