Ask a Scientician

Janelle’s second question was aimed at Bret (our resident animal expert) and me.

Have there been any significant changes to farm animals’ biology and behavior in the last few decades due to the increased use of growth hormones? Could our interference actually change or speed up their evolution as a species?

I am ill-equipped to answer the first part of that question. The second part I think I can take a stab at.

Our interference in the development of any domesticated species (cats, dogs, cows, pigs, etc.) is affecting the evolution of those species. Dogs are an excellent example of what selective breeding and isolate populations can produce. While all dogs are still technically the same species, it is physically impossible for some breeds to reproduce (think St. Bernard and Chihuahua).

The increased use of growth hormones (and I assume you were thinking of cows in this example) can have an effect on the development of the species. Again, I’ll have to defer to Bret to talk about significant changes in the animals themselves. From a moelcular biology perspective (which is where I usually sit) the addition of an exogenous hormone will change gene expression and protein production in the cows. The intended consequence is increased milk production or better quality beef. Because of the complexity of the systems and the uncertainty of long-term effects on the animals, there may be additional changes that we are unaware of.

Biological systems like to find an equilibrium. When something is added (external hormone, genetic activation) or knocked out (gene knockout animals are common in research) there are compensatory changes in the animal. Other pathways, genes, and proteins will be activated/deactivated in unexpected ways to attempt to create a “normal” functioning animal.

Cows injected with hormones will almost certainly develop a resistance to the chemcial (regardless of whether it is a normally-occuring hormone or not) and will find a balance of self-regulation that will try to keep the cow in “cow form” as much as possible.

If this is extended over may generations and in an isolated population, it may begin to select for genes and pathways that are not normally expressed in cows. So, yes, there is the potential for accelerating the evolution of animals through these treatments.