Monday, August 31, 2009

Is evolution still happening?

Every so often, someone lands on my site specifically because they're wondering this: is evolution still happening?

Depends what you mean, really.  We hear often how viruses and bacteria mutate, seeming to generate new ways to attack us all the time.  Take bacteria (which are more readily classed as living entities).  They proliferate by dividing (binary fission), and their generations are far, far more rapid than ours.  Greater population, fast breeding, more scope for genetic change that is more visible to us.

Yet broadly we conceive evolution in terms of how we humans got to where we are today.  And that's the product of hundreds of millions of years (and elaborated in my earlier discussion here).  Saying that is one thing, but understanding it is far more difficult, because our human scale takes its measure in one lifetime.  At best, we extend ourselves to the whole of human history, which is only a few thousand years - a tiny speck on the scale of hundreds of millions.  I call this issue deanthropocentrism: the effort required to conceptually escape our human framework, and understand processes that work on vastly different scales.  To do this more than superficially is not nearly as easy as it sounds.

So some of us think, how can this be, does this evolution really make sense?  Yes, it does, just not so much in our immediate framework.

Yet the sun is still emitting radiation that occasionally knocks around with DNA in our germ-line cells, producing the odd change.  Such changes can add up over time, if beneficial for survival.  If a mutation improves the odds of an individual surviving and breeding, that mutation is more likely to survive.  In the past, this was "natural selection" - ie, mutation survived where the "whole of environment" (including climate, food resources, food competitors, and predators) fostered it.  These days, humans frequently take that role, exercising selectivity over both plant and animal breeds.

How does selectivity work today on humans?  Well, we've diluted it substantially.  By improving global health, we're over-riding natural selectivity.  We're increasing the survival rates of those who have adverse genetic outcomes.  For example, cystic fibrosis sufferers once seldom lived far beyond puberty, but survival has now been prolonged past breeding age.

Is that a bad thing?

No, because we are ethical beings, not ones to ride on the whim of random outcomes.

Over time, our technology can improve outcomes, identify potential issues before they happen, find solutions.

And we are now at the point where the environment is a product of us, not vice versa.  So what of climate change?  Although we can say human adaptions that are better suited to a hotter, more turbulent world are better able to survive, the question is whether those less adaptive are likely to survive to breed.  And our global culture no longer fosters selectivity purely on that basis - bar a calamitous breakdown of society.

So these are the issues: whether and how we intervene in 'natural' selectivity.  Such intervention can bring human evolution to a halt.  The only selectivity for breeding now is societal, and I have seen no indication so far of any specific genetic determinant on those who end up remaining single all their lives (in the sense that they produce no offspring).

In that sense it could be said that humans, for the time being, have induced their own evolutionary pause.  However, that might not be such a bad thing: natural selectivity could work in any direction, depending on environment.  Bigger (or brighter, or more complex) is not necessarily better for survival, for example - as the dinosaurs found out.

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