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Evolution/Human evolution & intelligence


QUESTION: 1. Can you give me a brief summary of how evolution works and how our ancestors evolved from apes to having human intelligence?

2. Can evolution/science answer why only humans evolved to have intelligence?  

It's a little bit like why lions are the ones to evolved to have prides, where leopards, cheetahs who are much weaker hunt and defend for themselves.

ANSWER: Dear Samantha,

There's really no such thing as a brief summary of how evolution works.  Organic evolution, the evolution of living populations over generations, can proceed by several mechanisms, and you can find an overview of how those mechanisms work here:

As to your second question:  humans are *not* the only animals that have evolved to have intelligence.  Our intelligence may be greater than that of most other species, but many species have problem-solving capabilities, the ability to recognize themselves in a mirror, and other criteria considered important for an organism to be called "intelligent".  The closer relatives of humans, such as chimpanzees, gorillas, and orangutans, have what most humans would recognize as a human-type of intelligence, though not to the degree that our species has with our big, trouble-making brains.

In short, species don't evolve things because they "need" them.  Traits remain in a population because they appear by chance mutation(s).  Any trait can be:

adaptive - increases the likelihood that the organism bearing it will survive and reproduce
maladaptive - decreases the likelihood that the organism bearing it will survive and reproduce
neutral - does not affect the likelihood that the organism bearing it will survive and reproduce

Darwin's theory of evolution by means of natural selection states that organisms with adaptive traits will leave more offspring than those lacking those traits.  Over generations, that trait will thus increase in frequency in the population, and the population will thus evolve.

Genetic drift is another mechanism by which organisms can evolve, but that is not likely to be a good explanation of why humans have such big brains, high intellgence, and all the dressing that goes along with that.

One compelling idea is that our large brains are the product of sexual selection:  our ancestors preferred to choose mates who were intelligent (and had behaviors that "showed off" that intelligence), and so--like the peacock's tail--our brains grew bigger and more intelligent than we needed to have them simply to survive.  If that's true, then our brains are a bit like the lion's mane or the peacock's tail.  :)  While Geoffrey Miller is not the only scholar to have put forth this idea, his book, The Mating Mind, gives a good overview of how this could have happened.

The really short answer:  traits evolve because they work and the genes that encode them thus promote their own descent into the next generation.  For some interesting tutorials on evolution, please visit:

Hope that helps.


---------- FOLLOW-UP ----------

QUESTION: What do you think of the doc called What Darwin never knew by PBS and Origin of us by BBC?

They talked about switches in our dna and climate change making the switches turn on and off through evolution.

1. How accurate is it?
2. In the doc they mentioned something about our human thumb being a major cause to allow our ancestors to grow larger brains, do you agree?

Hi, Samantha

I just *love* "What Darwin Never Knew", but I haven't seen the other one.  I'm intrigued, though.  I'll have to pick up a copy of "Origin".

When you ask "how accurate is it", I have to ask back:  Which part?  I saw nothing in WDNK that seemed unsupported, though some of this is still hypothetical.

I haven't seen the documentary that says the human thumb could have triggered the increase in our brain size, but just that statement sounds kind of Lamarckian to me.  I'd have to know their reasoning, unless they're talking about epigenetic changes.

There are so many theories floating around out there about why we have such big brains that you can pretty much take your pick.  As for me, I really like Geoffrey Miller's idea.  A lot of what we are is a product of sexual selection, and it makes complete sense that "runaway sexual selection" could--at least in part--have contributed to our ridiculously big, problematic brains.




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Dana Krempels


I can answer questions about evolutionary mechanisms and theory, including genetic drift, mutation, natural selection, etc. I also can clear up misconceptions about evolution as it's sometimes talked about by those not well-versed in the subject (e.g., some politicians and many religious fundamentalists).


I have a Ph.D. in Biology, and presently teach Evolution and Biodiversity, Genetics, Botany, and Zoology at the University of Miami.

House Rabbit Society Beta Beta Beta Biological Honor Society

Exotic DVM Magazine (veterinary journal)

B.S. in Biology B.A. in English Ph.D. in Biology

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