Expert: John Shea - 1/31/2004

Question
Dear mr shea my name is Mathew I am 10yrs old. I am doing a school project on evolution and I am trying to figure out what humans might evolve into. I want to end my project with a picture of what we might evolve into. say people with giant heads and little bodies. can we tell what we will look like? what is your idea?
thankyou,
Mathew  

Answer
Hi Matthew
This is a very complex and complicated issue. I'll give you a brief explanation, but if it sounds too technical, ask your parents or teacher for help with the vocabulary.
First off, large populations (like humans) evolve very slowly, through minor changes in gene frequencies.  So, unless something happened to both reduce the overall human population and/or to isolate a large population of humans from the rest of humanity (500-1000 people = minimum viable population) , there probably won't be any major changes in human form as the result of natural selection. The only kind of event that could reduce and fragment human populations low enough to get major evolutionary changes would be some sort of major natural catastrophe, e.g., asteroid impact, rapid onset of glacial conditions, pandemic disease.  The other possibility, of course, is that if humans colonize other star systems, those populations could be so isolated from Earth that genetic differences would accumulate, making it difficult for them to reproduce with people from Earth.  (My guess, though, is that anybody smart enough to figure out interstellar travel would probably take along DNA samples, to maintain genetic diversity in colonizing human populations.)
Here on Earth, for the present, we're pretty well insulated from the kind of natural forces that cause major morphological change (climate, disease, predators, competitor species). When you relax natural selective pressure the usual result is increased genetic and morphological variability.  So, you might reasonably expect a wider range of genetic and morphological variabilty among future human populations.  (For a case in point, you can point to people living today who have overcome crippling genetic problems in childhood.  In prehistoric times, these people would probably not have survived.  For a pretty good science fiction treatment of future human evolution, look up Dougal Dixon's book Man After Man.
There probably won't be any people with big heads/huge brains, like you see in science fiction movies.  Big brains cause complications at birth, and we have technology (computers) that can perform many of the same functions as increased brain size.
Where you might see major morphologial evolutionary change among humans would be through genetic engineering and biomechanical engineering to solve problems left over from the course of human evolution.  There is a pretty good paper about this in a 2003 Special Edition of Scientific American ("If humans were built to last").  Check your library, they probably have this.
I hope this helps.  Good luck with your research.
John Shea
Associate Professor
Anthropology
Stony Brook University