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Tim Karr

Assistant Professor/Biology and Anatomy
University of Chicago
Illinois, USA

Timothy L. Karr, PhD is an assistant professor of biology and anatomy at the University of Chicago.  He is a member of the Department of Organismal Biology and Anatomy and committees on Developmental Biology, Evolutionary Biology, and Genetics.  As a scientist, he researches Giant Killer Sperm.  Here, he shares with us, his fascination with biology and the world of drosophila.

Did you always want to be a scientist?

Yes, I always wanted to be a scientist.  I did my first experiment at the age of 6 (I grew up in the Arizona desert and wanted to know why water disappeared so fast when left in the sun...).  I never really entertained any other careers when growing up.

When did you first become interested in biology?

My interest in biology came naturally in a desert setting.  I remember vividly all of the desert insects, lizards and other crawly creatures (spiders and scorpions) and how I loved to just watch them.  Desert ants were especially fascinating.  Also, our ranch animals- dogs, cats, goats and donkeys- often gave birth and it was fascinating to watch not only the birthing process, but the care given afterwards.

What where your favorite subjects in elementary and high school?  Which subjects prepared you best for your career today?

Math and science, particularly biology.  I think the analytical tools I learned in my high school math classes, particularly geometry and calculus were key to preparing for an academic career.

What do you find most interesting about biology?

The study of organisms, how they reproduce and maintain their fragile foot hold on life, and how they adapt over time are the most interesting to me.  I am particularly fascinated by how groups of organisms enter into associations with each other to more effectively compete.  This is known in its broadest sense as 'symbiosis'.  Symbiosis has been a dominant force in the evolution of species for over 1.5 billion years.

What subjects do you teach?  What careers are people who take your classes typically entering?

At the undergraduate level, I teach a basic, interdisciplinary course in biology.  This is a very broad introductory course that touches on many topics of biology.  Most students are looking for careers in either medicine or basic research.

Approximately what percentage of your students are women?  Do many women enter your field?

There is a very nice 50/50 mixture of genders at the University of Chicago in the biological sciences.  Certainly women enter my field (and do EXTREMELY well!).

What do you research and study?

I am interested in a symbiotic association between insects and a bacterium.  This bacterium is very clever and uses its host (an insect) to further its own propagation by altering the way they reproduce.

I am also interested in another topic - giant sperm.  Many species of insects produce extremely elongated sperm, many hundreds of times longer than human sperm.  This is an example, many of which can be found in nature, of an "absurdity without an explanation".  For example, why would an adult male caribou (or elk) carry on their head over 50 pounds of antlers?  They are huge, gaudy and take an enormous amount of energy to carry around.  Plus, just like the peacock's extremely large, colorful and beautiful tails, they make it easier for natural prey to spot them.  So, why do it?  Many times these "absurdities" are explained by complex sexual selection processes that are poorly understood, but by studying them we can gain insights into the evolutionary processes that produced them.

What do people say when you tell them that you study "giant sperm"?

You can imagine I get some odd looks, giggles and expressions of incredulity!

What are drosophila and what makes them so interesting to study?  Why do you study their sperm?

Drosophila are a genus of two-winged insects (known as dipterans).  They are closely related to the common house fly, and more distantly related to wasps and bees.  They are not really all that interesting(!), but they are tremendously convenient to study.  Biologists decided about 100 years ago that most of the efforts in the area of insect genetics would focus on Drosophila.  They were chosen because they are small, reproduce very rapidly and therefore inexpensive to rear in the laboratory.  I have explained somewhat above why I am interested in giant sperm. Another general reason to study sperm (or eggs) is because it is one of the most BASIC and universal feature of almost all animals.  In order to survive, a species must reproduce.  To do so, one sex must make a sperm and one an egg.  Although very simple to state in words, we still do not know why there are sperm and eggs!  Or how and when they arose in evolutionary history.  It is one of the great unsolved mysteries of biology.

How does the size of the sperm compare with the size of the insect?

Some species of Drosophila make sperm that are 50 times the length of their entire body!

What does your family think of your job and your research?

I am very fortunate to have a wonderful wife, son and daughter who have always supported me.

Do you have any pets?

Lucy is the most loving, vibrant 13 year old beagle mix in the entire world!  We have had her every since she was about a year old.  We got her from the animal shelter (she had been abused) and she has turned out to be the best pet our family has every had.  She still walks with me everyday into the lab and she sleeps on a sofa in my office.

What do you do for fun?

Research Drosophila! what else??  Well, sometimes I spend weekends with my family visiting all the interesting museums, art galleries and other fun things to do in Chicago (one of our favorite things is to get up early on Sunday morning and go downtown for a big breakfast and then spend a few hours at the Lincoln Park Zoo- an amazing zoo, made even more amazing by the fact that admission is FREE!).

Do you have any advice, encouragement or words to share with learners around the world?

Just be grateful that you are blessed with the mind, the curiosity and the motivation to learn- it is our most precious "natural resource!".

Recommended web sites:

The Karr Lab - Home of the Giant Killer Sperm

The Karr Lab - People

Introduction to Drosophila

Interactive Fly, Drosophila

The Fruit Fly in You

Tim responds to questions

- 4 March 2002


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Last Updated:
5 May 2002

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