Could we have evolved traits that are detrimental to our survival?

Let us assume that we collected data on the presence or absence of a trait (e.g., propensity toward risky behavior) in a population of individuals, as well as on intermediate effects of the trait, downstream effects on mating and survival success, and ultimately on reproductive success (a.k.a. “fitness”, in evolutionary biology).

The data would have been collected over several generations. Let us also assume that we conducted a multivariate analysis on this data, of the same type as the analyses employing WarpPLS that were discussed here in previous posts (). The results are summarized through the graph below.



Each of the numbers next to the arrows in the graph below represents the strength of a cause-effect relationship. The number .244 linking “a” and “y” means that a one standard deviation variation in “a” causes a .244 standard deviation increase in “y”. It also means that a one standard deviation variation in “a” causes a 24.4 percent increase in “y” considering the average “y” as the baseline.

This type of mathematical view of evolution may look simplistic. This is an illusion. It is very general, and encompasses evolution in all living organisms, including humans. It also applies to theoretical organisms where multiple (e.g., 5, 6 etc.) sexes could exist. It even applies to non-biological organisms, as long as these organisms replicate - e.g., replicating robots.

So the trait measured by “a” has a positive effect on the intermediate effect “y”. This variable, “y” in turn has a negative effect on survival success (“s”), and a strong one at that: -.518. Examples: “a” = propensity toward risky behavior, measured as 0 (low) and 1 (high); and “y” = hunting success, measured in the same way. (That is, “a” and “y” are correlated, but “a”=1 does not always mean “y”=1.) Here the trait “a” has a negative effect on survival via its intermediate effect on “y”. If I calculate the total effect of “a” on “w” via the 9 paths that connect these two variables, I will find that it is .161.

The total effect on reproductive success is positive, which means that the trait will tend to spread in the population. In other words, the trait will evolve in the population, even though it has a negative effect on survival. This type of trait is what has been referred to as a “costly” trait ().

Say what? Do you mean to say that we have evolved traits that are unhealthy for us? Yes, I mean exactly that. Is this a “death to paleo” post? No, it is not. I discussed this topic here before, several years ago (). But the existence of costly traits is one of the main reasons why I don’t think that mimicking our evolutionary past is necessarily healthy. For example, many of our male ancestors were warriors, and they died early because of that.

What type of trait will present this evolutionary pattern – i.e., be a costly trait? One answer is: a trait that is found to be attractive by members of the other sex, and that is not very healthy. For example, a behavior that is perceived as “sexy”, but that is also associated with increased mortality. This would likely be a behavior prominently displayed by males, since in most species, including humans, sexual selection pressure is much more strongly applied by females than by males.

Examples would be aggressiveness and propensity toward risky behavior, especially in high-stress situations such as hunting and intergroup conflict (e.g., a war between two tribes) where being aggressive is likely to benefit an individual’s group. In warrior societies, both aggressiveness and propensity toward risky behavior are associated with higher social status and a greater ability to procure mates. These traits are usually seen as male traits in these societies.

Here is something interesting. Judging from our knowledge of various warrior societies, including American plains Indians societies, the main currency of warrior societies were counts of risky acts, not battle effectiveness. Slapping a fierce enemy warrior on the face and living to tell the story would be more valuable, in terms of “counting coup”, than killing a few inexperienced enemy warriors in an ambush.

Greater propensity toward risky behavior among men is widespread and well documented, and is very likely the result of evolutionary forces, operating on costly traits. Genetic traits evolved primarily by pressure on one sex are often present in the other (e.g., men have nipples). There are different grades of risky behavior today. At the high end of the scale would be things that can kill suddenly like race car driving and free solo climbing (, ). (If you'd like to know the source of the awesome background song of the second video linked, here it is: Radical Face's "Welcome Home".)

One interesting link between risky behavior and diet refers to the consumption of omega-6 and omega-3 fats. Risky behavior may be connected with aggressive behavior, which may in turn be encouraged by greater consumption of foods rich in omega-6 fats and avoidance of foods rich in omega-3 fats (, ). This may be behind our apparent preference for foods rich in omega-6 fats, even though tipping the balance toward more foods rich in omega-3 fats would be beneficial for survival. We would be "calmer" though - not a high priority among most men, particularly young men.

This evolved preference may also be behind the appeal of industrial foods that are very rich in omega-6 fats. These foods seem to be particularly bad for us in the long term. But when the sources of omega-6 fats are unprocessed foods, the negative effects seem to become "invisible" to statistical tests.

We share an ancestor who probably lived no more than 640 years ago

This post is a revised version of a previous post. The original post has been or will be deleted, with the comments preserved. Typically this is done with posts that attract many visits at the time they are published, and whose topics become particularly relevant or need to be re-addressed at a later date.

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We all evolved from one single-celled organism that lived billions of years ago. I don’t see why this is so hard for some people to believe, given that all of us also developed from a single fertilized cell in just 9 months.

However, our most recent common ancestor is not that first single-celled organism, nor is it the first Homo sapiens, or even the first Cro-Magnon.

The majority of the people who read this blog probably share a common ancestor who lived no more than 640 years ago. Genealogical records often reveal interesting connections - the figure below has been cropped from a larger one from Pinterest.

You and I, whoever you are, have each two parents. Each of our parents have (or had) two parents, who themselves had two parents. And so on.

If we keep going back in time, and assume that you and I do not share a common ancestor, there will be a point where the theoretical world population would have to be impossibly large.

Assuming a new generation coming up every 20 years, and going backwards in time, we get a theoretical population chart like the one below. The theoretical population grows in an exponential, or geometric, fashion.

As we move back in time the bars go up in size. Beyond a certain point their sizes go up so fast that you have to segment the chart. Otherwise the bars on the left side of the chart disappear in comparison to the ones on the right side (as several did on the chart above). Below is the section of the chart going back to the year 1371.

The year 1371 is a mere 640 years ago. And what is the theoretical population in that year if we assume that you and I have no common ancestors? The answer is: more than 8.5 billion people. We know that is not true.

Admittedly this is a somewhat simplistic view of this phenomenon, used here primarily to make a point. For example, it is possible that a population of humans became isolated 15 thousand years ago, remained isolated to the present day, and that one of their descendants just happened to be around reading this blog today.

Perhaps the most widely cited article discussing this idea is this one by Joseph T. Chang, published in the journal Advances in Applied Probability. For a more accessible introduction to the idea, see this article by Joe Kissell.

Estimates vary based on the portion of the population considered. There are also assumptions that have to be made based on migration and mating patterns, as well as the time for each generation to emerge and the stability of that number over time.

Still, most people alive today share a common ancestor who lived a lot more recently than they think. In most cases that common ancestor probably lived less than 640 years ago.

And who was that common ancestor? That person was probably a man who, due to a high perceived social status, had many consorts, who gave birth to many children. Someone like Genghis Khan.

Bolt vs Farah at 600m. The extremes meet, who wins?

Bolt vs Farah over 600m: The extremes meet in the middle (kind of, physiologically...)

For athletics fans, the prospect of Usain Bolt vs Mo Farah over 600m offers an enthralling spectacle where the most dominant athletes at the extremes of track running test themselves with one foot in the other’s domain.  I suspect it is highly unlikely to happen, but it's a great platform for some debate around performance physiology.

Predicting the winner is a fun exercise in stats, performance analysis and physiology (performance analysis - it's not an exact science, remember!).  

The fascinating question for this one is where do the physiologies of these two “extreme” athletes cross?  Of course, bear in mind that there are athletes in the middle who would arguably beat both Farah and Bolt over 600m, and by a long way.  When David Rudisha broke the 800m WR in London last year, his 600m split time was 1:14.3, and that's about as fast as I suspect Farah or Bolt could run in a straight 600m.  

Rudisha's 1:40.91 predicts something under 1:12 for 600m (the world record is 1:12.81, and that's from Johnny Gray, who was 1.6 seconds slower than Rudisha at his best), so he would certainly win a 600m were he in it.  In fact, so would just about the entire men's 800m Olympic final field, and a good few 400m, 400m hurdlers and 1500m runners (the 800m/1500m combo guys) too - this 600m is not about finding the best athlete, but about some fun and publicity!

Physiology at the 'extremes'

Physiologically, making the prediction invites some discussion over the origin and capacity of the energy pathways used by each, and what it means for fatigue. 

It boils down to different questions for each man.  For Bolt, it’s whether he can withstand the fatigue of going three times further than his normal race distance, and how much he would need to slow down to avoid complete failure to even finish the distance?

For Farah, it’s whether his top speed is high enough to pressurize Bolt into that premature fatigue? 

A quick physiological lesson will explain:  When you see athletes tying up and slowing down dramatically at the end of a sprint race, what you are witnessing is the combination of a "failure" of energy production (the supply can't meet the demand), a build up of metabolic by-products in the muscle and the central and peripheral responses to these changes.  Nobody knows the full explanation for this, and it’s likely more complex than any current theory can explain, but the result is a reduction in muscle contractility with sub-maximal muscle recruitment.  

Studies have shown, for instance, that at the end of a 400m race, drop-jump performance declines by 39% and that muscle activation increases, which shows the cumulative effects of fatigue on muscle function - more recruitment needed for less force/power.  Other studies show that this happens despite pacing, and the presence of some muscle unit reserve, which implies that fatigue occurs partly in the brain, partly in the muscle.

The source of energy is crucial to both fatigue processes, because it affects the biochemical changes occurring in the muscle.  Bolt and Farah rely on different pathways for their energy.  Bolt has a highly developed pathway that produces the energy needed for muscle contraction very rapidly, but not for very long.  His energy comes primarily from what are known as oxygen independent (or anaerobic, though this word is avoided by many) pathways.  They are all about the speed of energy supply, and the consequence – a build up of metabolites, is an accepted downside because he doesn’t need more than 20 seconds of explosive power. 

Farah, on the other hand, can produce energy for hours, but more slowly, using primarily oxygen dependent, or aerobic pathways.  The upside is less peripheral accumulation (though glycogen depletion is, eventually, a theoretical 'limit'), the downside is the rate of supply.  This difference accounts for the clear differences in the optimal pacing strategy between short duration and long-duration events, something I summarized in this review article for BJSM.

There is always an overlap, with some contribution from both pathways, no matter the distance, but for shorter, high intensity exercise like sprinting, the oxygen-independent pathways are more heavily relied upon (in the 200m event, for instance, the split is around 70%-30% in favor of energy production without oxygen.  By 1500m, it is reversed to 30%-70%). 

So, as much as Bolt and Farah lie at the opposite ends of the performance spectrum, they are also extremes of biochemistry.  Muscle histology and function also differ – Bolt’s are more contractile, able to contract rapidly and forcefully, but they also fatigue more rapidly.  

The prediction

Over the nominated distance of 600m, Farah would be forced to find a force and speed of muscle contraction and energy production that he is unfamiliar with, while Bolt will be asking his biochemistry to withstand an accumulation of metabolites and resultant fatigue that he is also unaccustomed to.

As for a prediction, the biochemical odds are slightly tilted in Farah’s favor at 600m.  A number of people have attempted to model where the perfect distance is, and using the above-mentioned energy pathway models, have estimated that the perfect distance, with equal performances, lies somewhere between 500m and 550m.   

Those additional 50m, seemingly trivial, probably just give Farah the edge and represent 50m too far for Bolt’s physiology.  Farah’s famous finishing kick, as well as his recent 1500m performance, a European record of 3:28, have shown that he has extra-ordinary sustained speed for a distance runner, so the biochemical “jump” to a 600m may not be as large as the step up from 200m to 600m for Bolt. 

On that performance note, Farah's 600m performance is easier to predict and is more familiar to him - it's something he'd do regularly in training, whereas Bolt would very rarely approach even sub-maximal efforts for this duration.  

Performance-wise, Farah's 3:28 suggests that his 800m performance would be in the range of 1:45 to 1:46.  That would optimally be achieved with a 51-52s first lap, and a 53-54s second lap.  That in turn suggests that a very fast 400m of 49s would be possible.  Then it becomes a question of limiting the slow down, and finishing with a time around 1:14-1:15.  It's about starting fast enough to take advantage of sustainable speed and attenuated slowing down at the end.

Bolt, on the other hand, has to worry about the opposite problem - not starting too fast.  He has run 400m in under 46s almost every year since 2007, including a PB of 45.28s six years ago, and a 45.35s at the age of only 17.  So he may have the natural ability, if he judges the pace well, to edge Farah.  However, six years is a long time, and those low 45s are probably less relevant now, particularly since he has probably gained mass since 2007.  Mass hurts over longer distances, so Bolt has this to deal with as well.  If Bolt does go out in 48s, gaining an advantage of around a second over Farah, he'd need to hold on to around 27s for the final 200m, and I suspect that would be a little too much to ask.

With a month of dedicated training for the 600m distance, my money would be split.  In my opinion, it would be a coin toss - Bolt would be able to change the training enough to adapt just enough to make it incredibly close.  But, if the race were to happen straight after their specialized seasons, Farah has the edge.  I'd pick Farah by about half a second to a second.  Over 550m, maybe it comes down to the lean.  It would be a fascinating meeting of two extremes.  It would sure be fun to watch, and discuss - that happens over on Twitter and Facebook!

Ross