The changes during puberty take place slowly over months and years. For example, facial hair growth in boys starts with a few scattered hairs and gradually becomes more uniform.

These changes do not occur at the same time or at a specific age for everyone. The onset and pace can vary widely among individuals.

Boys develop new thick hair on the face, experience voice cracking, and may witness occasional enlargement and erection of the penis, often in daydreams or at night.

Girls experience an increase in breast size and darkening of the skin of the nipples. Menstruation also begins during this period.

If DNA copying mechanisms were less accurate, many resultant DNA copies might not function properly within the cellular apparatus, leading to cellular dysfunction or death.

The process of making variants is accelerated by the accumulation of variations in DNA copies across generations. Each new variation occurs in a DNA copy that already carries accumulated variations from previous generations.

Accumulating variations in living individuals ensures that these variations do not have immediately detrimental effects. This gradual process allows for the preservation of functional traits while introducing novel variations over time.

Sexual reproduction involves the combination of DNA from two different individuals during reproduction. Since each individual has accumulated a unique set of variations, the combination of their genetic material results in novel combinations of variants, fostering genetic diversity within populations.

The difficulty arises from the potential accumulation of twice the amount of DNA in each new generation, which could disrupt the control of the cellular apparatus by the DNA.

Reproductive modes that allow for the generation of more variation, such as sexual reproduction, increase the pool of genetic diversity within a population. This diversity acts as a reservoir of potential traits, promoting the survival of the species by increasing ...