Why do giraffes have long necks?

One of the things I've learned from studying history is that concepts that fell out of favor in the past never seem to go completely away.  It's a topic that I've discussed a number of times in the past (see "Past is Prologue", "Study the past", "...all of this has happened before", and "The past is never dead...").  As the philosopher, George Santayana famously said, "Those who cannot remember the past are condemned to repeat it."  

Look no further than the concept of Lamarckian Inheritance or Lamarckism, the concept that physical and personal improvements that humans acquire during their lifetime can be passed down to their children in subsequent generations.  The French zoologist Jean-Baptiste Lamarck first proposed the concept describing the inheritance of acquired characteristics in 1809.  Lamarck famously argued that a blacksmith's sons inherit the strong muscles that he acquires from his work as a blacksmith.  

Lamarck's ideas began to fall out of favor with Charles Darwin's theory of evolution by natural selection, first described in his book, On the Origin of the Species in 1859.  Lamarck would say that early giraffes continually stretched their necks to reach the highest leaves in the trees by physically stretching their necks.  The physical stretching caused their necks to grow, which was passed on to as a "longer neck" to subsequent generations.

In contrast, Darwin's theory of natural selection would explain that some giraffes would be born with a longer neck by random chance.  These giraffes would be able to reach more food higher up in the tree.  The longer neck conferred a survival advantage, allowing these giraffes with the longer necks to pass on their genes to subsequent generations, who would in turn have longer necks.  Over time, the giraffes with the longer necks "replace" the giraffes born with the shorter necks.

Lamarckian Inheritance has also been called "soft inheritance" to differentiate from the so-called "hard inheritance" that occurs via the transmission of genetic mutations to subsequent generations.  What's interesting is that we now know that at least some acquired characteristics can, in fact, be passed down to subsequent generations via a mechanism known as transgenerational epigenetic inheritance.  "Transgenerational epigenetic inheritance" describes the process by which environmental factors, such as stress or diet, can affect gene expression in such a way that these changes are passed down to future generations.  More generally, "epigenetics" describes the way that changes in gene expression occur without altering the underlying structure of DNA (basically, the chemical structure of the genes themselves).

I came across a recent report in Nature Reviews Urology that suggests Lamarck may have been at least partially correct, at least when it came to the blacksmiths passing down their strong muscles to their children.  The report comes on the heels of evidence showing that physical exercise can trigger epigenetic changes in muscle that can be passed on to subsequent generations.  In other words, mothers who exercise during pregnancy can pass on some of their overall fitness and health to their children.  The current study shows that fathers can pass on some of the epigenetic changes associated with fitness via their sperm through so-called exercise-responsive microRNA (miRNA), similar to what has been observed with mothers who exercise during pregnancy.  As the authors of the study conclude, "...in addition to well-established maternal influences, paternal exercise before conception can shape the metabolic trajectory of offspring, pointing to the paternal germline as a biologically meaningful conduit of environmental information."

I think there are two points that I would like to make here.  First, once again, we see an older concept, one that was even widely discredited at one point, come back, albeit in a re-packaged form, with new knowledge advances.  It's a common scenario that I frequently encounter both in my clinical practice and in my administrative one.  Second, one can only wonder if we will ever find certain leadership traits passed down from one generation to the next?  I've mentioned a study in the past (see my post, "Once again...are leaders born or made?") that found that genetic factors explained 24% of the difference between individuals in leadership occupancy in a large clinical database (specifically the single nucleotide polymorphism found at rs4950 on the CHRNB3 gene.  Specifically, having one more rs4950 A allele (instead of a G allele) increased the odds of being in a leadership role by 50 percent!  One wonders if we will find certain epigenetic modifications in so-called "leadership genes" that can be passed down from one generation to the next.  It sounds far-fetched now, but then, no one probably ever thought that a study would show that physical fitness can be transmitted to our children either!