Question About Human Evolution

[Barnes]

Hi all. I signed up just to ask this question. I only know basic knowledge about this topic, and a thought just occurred to me.

 

The human being takes roughly eighteen to twenty years until it becomes fully grown. Or something like that.

 

For most animals, it seems to take no more than two years.

 

Why does the human take longer to become fully grown than say a chimpanzee? Is it because humans, as the most evolved species (I guess), need more years as infants to fully develop into grown adults?

 

I may have just answered my own question, but can anyone confirm this for me?

 

Hopefully you understand what I'm saying, but it's hard to put into words.

 

Thanks

[Arete]

Why does the human take longer to become fully grown than say a chimpanzee? Is it because humans, as the most evolved species (I guess), need more years as infants to fully develop into grown adults?

 

1) No one organism can be described as the "most evolved species". Evolution is not a directed process, mutations are random and the enviroment simply dictates which ones are successful and which aren't. Plenty of organisms undergoing adaptive radiation have far more phenotypic diversity and deviation in terms of phenotype from their common ancestor e.g. the Hawaiian Silverswords http://ohia.org/ohia...s/sky/adapt.htm

 

2) Generation times vary because selection pressure on rapid maturity is variable - often due to differential longevity of organisms. Humans live longer than chimps and thus have longer to produce viable offspring, so there is less selective pressure on rapid sexual maturity. For example - most albatross species live for approx 50-60 years and breed for most of their lives, thus reach sexual maturity at around 8 years of age. Zebra finches can reach sexual maturity in 2 months, but only live for five years. Galapagos tortoises don't reach sexual maturity until 25 years of age.

Edited July 12, 2012 by Arete