Expert: Florence M Rollwagen - 5/19/2008

Question
QUESTION: Hello. I have recently found myself very interested that cats and other animals can see much better in the dark than humans. i know that this is mainly because they have cones and rods and the tapetum lucidum but i was just wondering, have any experiments been done on humans to increase the amounts of cones and rods or to add a tapetum lucidum? Sorry if this sounds ridiculous, im just really interested. Also if humans are meant to be the most advanced animals in the world why have we not had small evolutions like other animals over time? say to get night vision? or are we still evolving? Thank you for all your help.

ANSWER: Hi Leigh, thanks for your question.

Your statement "if humans are meant to be the most advanced animals..." is an anthropomorphic way of looking at life.  Most scientists don't see evolution this way.  Each animal/plant is adapted to its niche in life by virtue of natural selection.  To ask why don't humans have night vision is like asking why humans don't have a trunk, or wings.  

Actually, humans have been evolving over time, it's just that our recorded history is too short to document these changes.  Here are a couple of changes that we do know about:

1.  Evolution of the CCR5 receptor.  During the Black Death (smallpox) in Europe in the 1300s a sub-set of the population did not die.  This sub-set had a mutation in a key immunological receptor on white cells, called the CCR5 receptor.  So the population of Europe that survived to today mostly have this mutation.  Well, it turns out that HIV (the virus that causes AIDS) also uses the CCR5 receptor to enter cells.  The Europeans who had this mutation were resistant to smallpox, and now, by coincidence, to HIV.

2.  Evolution of the sickle cell gene.   In Africa, malaria kills many children, and is deadly to adults as well.  Some Africans have a mutation in their hemoglobin gene, called sickle cell, that prevents the malaria parasite from infecting the host.  People with this gene are somewhat resistant to malaria.  But the gene is lethal if the child inherits it from both parents.  So here is the dilemma: Die from malaria without the gene, die from inheriting the gene from both parents, BUT live and produce children if you inherit only one copy of the gene.

So when we speak of evolution, we have to think of the environment in which the animal/plant lives.  Cats are nocturnal.  Long ago, animals that had efficient night vision survived better than those who didn't.  They passed on their night vision genes to their cat children, who passed it on to the next generation.

Evolution is all about selecting the right genes for the right environment.  We don't have night vision because our ancestors didn't need it.

If you'd like to research this more, investigate "artificial retina" in Google.

I hope this answer has helped you.  Please write back if you have more questions.

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

QUESTION: Wow. that was highly interesting. thanks for answering my question. but just one more thing, if a human were to become nocturnal, would their body adapt somehow and their night vision get better? or would this take many year to happen within a nocturnal family or something else?

Answer
If environmental forces were such that humans had to become nocturnal (note I didn't say CHOSE to become nocturnal), several things would happen.  Individuals don't adapt to the environment, populations adapt.

1.  Those individuals today with superior night vision would survive and pass their night vision (NV) genes along to their children.

2.  Remember that there is variation in every generation, some will be better/worse in NV than others.

3.  Those children with superior NV would themselves have children with variable NV ability.

4.  Those who had superior NV would survive and pass their NV genes along to their children.

5.  Repeat #4 for 10,000 years.

6.  Then you might have a subgroup with superior NV

Each generation would get progressively better with night vision because the poor vision individuals would be weeded out by natural selection.  We also have to assume that the environmental pressures that forced night vision upon this population would still be in effect.

Evolution is a long slow process taking place over thousands or millions of years.  

Hope this helps.  This is an interesting topic.

FM Rollwagen, PhD