Life-history traits are often shaped by a balance between somatic maintenance and reproductive investment. That is, an individual wants their own cells to be active, but also needs to invest in making offspring. This tension between natural and sexual selection can generate age-related physiological trajectories that differ between organisms, environments and populations. In simpler terms, how you age is as much an evolutionary response to your environment as it is to your reproductive success!
Importantly, this tension can play out differently for males and females of a given species, especially when these traits are those that effect both reproduction AND survival. As I’m sure you can imagine, these traits can often be affected by the expression of other traits. For example: jumping, running and biting can all be important to an organisms survival, but also may be used as demonstrations of fitness that results in the attraction of mates. So when considering how aging differentially affects males and females, whole organism performance is perhaps the best way to measure full body traits.
And now I hope I’ve given sufficient information to introduce an interesting new study from Lailvaux et al. 2014, in which they look at whole body performance in basketball players from the National Basketball Association (NBA) and the Women’s National Basketball Association (WNBA) over time. The authors focus on aging in both male and female basketball players by measuring their points scored over the course of their career.
The authors compiled a data set of 1035 NBA players and 540 WNBA players, from 1979-2010. They look at height, minutes played, and points scored. Here points scored is acting for a proxy of whole body phenotypic performance, given that scoring captures a range of performance traits. They further broke down the type of points scored (two-point field goals, three-point field goals and free-throws), because different scoring types are a result of different whole-organism performance traits/abilities (burst speed, strength, visual accuracy) that interact differently as an individual ages.
Lailvaux et al. found two interesting things about how male and female basketball players age. 1) Men and women age differently and 2) the point types change over the lifetime of a play, and this is also different between men and women.
First of all, the age range for the WNBA players was narrower than that of the NBA, by about 10 years. The male athletes were routinely playing into their 40s while there were no women who were able to play that long. Over their lifetime, the NBA players showed a peak in performance around the age of 20, which rapidly declines until their retirement, while the female athletes have don’t have a peak as much as a consistent trend during their entire career (Fig. 1). The authors speculate that this could due to the more physically demanding NBA season (82 games vs. 34 games) year after year could take a greater toll on an NBA players body, and as such cause the decline in points seen by male basketball players but not female basketball players.
Additionally, as a player ages, they tend to shift their scoring to three point field goals instead of the other two types of scoring. Although this is reflected in both men and women, women tend to reach this point earlier, 25 instead of 30. The authors argue this reflects a possible aging compensation. The short duration, high intensity muscle movements that power jumping are known to decline with age. However, accuracy is a good substitute for power, and would give older players an edge in the three point range, as their two point scoring ability is on the wane.
Finally the authors note a potential effect of interactions between teammates. The NBA players on average are taller and score at higher rates than their female counterparts in the WNBA. However, the basket height is the same in both leagues, making “dunking” easier for males. Therefore, the authors speculate that WNBA play is more likely to emphasize cooperation among players than the NBA.
Overall, this is an exceptionally interesting article that not only brought up interesting aspects of aging, and full phenotype performance, but subtly brought up some issues of male vs. female professional athletes.
Lailvaux S.P., Wilson R. & Kasumovic M.M. (2014). Trait comparison and sex-specific aging of performance in male and female professional basketball players, Evolution, DOI: 10.1111/evo.12375