Clinical trials of CRISPR gene editing, when they start this year (2017), will edit existing cells in adults using an injection of a viral vector. It seems likely that CRISPR, or some improved version of it, will be established to be both safe and effective in the near future. Professor Stephen Hsu provides an analysis of the potential improvement from genetic editing compared to steroids.
Gene editing can make the genetically rare – the genetically common
Mike Israetel, a professor of exercise science at Temple University, has estimated that doping increases weightlifting scores by about 5 to 10 percent.
Compare that to the progression in world record bench press weights:
361 pounds in 1898,
363 pounds in 1916,
500 pounds in 1953,
600 pounds in 1967,
667 pounds in 1984, and
730 pounds in 2015.
Doping is enough to win any given competition, but it does not stand up against the long-term trend of improving performance that is driven, in part, by genetic outliers. As the population base of weightlifting competitors has increased, outliers further and further out on the tail of the distribution have appeared, driving up world records.
Lance Armstrong’s drug-fueled victory of the 1999 Tour de France gave him a margin of victory over second-place finisher Alex Zulle of 7 minutes, 37 seconds, or about 0.1 percent.3 That pales in comparison to the dramatic secular increase in speeds the Tour has seen over the past half century: Eddy Merckx won the 1971 tour, which was about the same distance as the 1999 tour, in a time 5 percent worse than Zulle’s. Certainly, some of this improvement is due to training methods and better equipment. But much of it is simply due to the sport’s ability to find competitors of ever more exceptional natural ability, further and further out along the tail of what’s possible.
Athletic performance follows a normal distribution, like many other quantities in nature. That means that the number of people capable of exceptional performance falls off exponentially as performance levels increase.
The normal distribution we see in athletic capabilities is a telltale signature of many small additive effects that are all independent from each other.
Estimates of the number of variants controlling height and cognitive ability, two of the most complex traits, yield results in the range of 10,000. If, as a simplification, we assume that in each of the 10,000 cases the favorable variant is present in roughly half the population, then the probability of random mating producing a “maximal” outlier is roughly two raised to the power of negative 10,000, or about one part in a googol (10 to the power 100) multiplied by itself 30 times. Of course it may not be possible to simultaneously have all 10,000 favorable variants, due to debilitating higher-order effects like being too large, or too muscular, or having a heart that is too powerful. Nevertheless, it is almost certain that viable individuals will exist with higher ability level than any person has ever had.
What are the physical limits ?
Selective breeding of corn plants for oil content of kernels has moved the population by 30 standard deviations in roughly just 100 generations. That feat is comparable to finding a maximal human type for a specific athletic event. But direct editing techniques like CRISPR could get us there even faster.
An increase in the average by one standard deviation (for example, 3 inches in male height, or 15 points in IQ), makes an individual at the 1 in 1,000 level (a 6-foot-7-inch male in the U.S. population) more than 10 times more likely.
20 standard deviations beyond current average IQ would be an IQ of 400.
20 standard deviations beyond current average height would be 11.5 feet.
30 standard deviations beyond current average IQ would be an IQ of 550.
30 standard deviations beyond current average height would be 14 feet.
The tallest human ever recorded was just short of 9 feet. The height did cause health issues.
The analysis of possible genetic improvement needs to look at the historical amounts of improvements and comparisons to animals for strength and speed and the physics of movement.
In 2010a study published in the Journal of Applied Physiology offers intriguing insights into the biology and perhaps even the future of human running speed. It offers an enticing view of how the biological limits might be pushed back beyond the nearly 28 miles per hour speeds achieved by Bolt to speeds of perhaps 35 or even 40 miles per hour. This could mean 100 meter times down at about 6-7 seconds.
In contrast to a force limit, what the researchers found was that the critical biological limit is imposed by time — specifically, the very brief periods of time available to apply force to the ground while sprinting. In elite sprinters, foot-ground contact times are less than one-tenth of one second, and peak ground forces occur within less than one-twentieth of one second of the first instant of foot-ground contact.
The researchers took advantage of several experimental tools to arrive at the new conclusions. They used a high-speed treadmill capable of attaining speeds greater than 40 miles per hour and of acquiring precise measurements of the forces applied to the surface with each footfall. They also had subjects’ perform at high speeds in different gaits. In addition to completing traditional top-speed forward running tests, subjects hopped on one leg and ran backward to their fastest possible speeds on the treadmill.
The unconventional tests were strategically selected to test the prevailing beliefs about mechanical factors that limit human running speeds — specifically, the idea that the speed limit is imposed by how forcefully a runner’s limbs can strike the ground.
However, the researchers found that the ground forces applied while hopping on one leg at top speed exceeded those applied during top-speed forward running by 30 percent or more, and that the forces generated by the active muscles within the limb were roughly 1.5 to 2 times greater in the one-legged hopping gait.
The new work shows that running speed limits are set by the contractile speed limits of the muscle fibers themselves, with fiber contractile speeds setting the limit on how quickly the runner’s limb can apply force to the running surface.
“Our simple projections indicate that muscle contractile speeds that would allow for maximal or near-maximal forces would permit running speeds of 35 to 40 miles per hour and conceivably faster,” Bundle said.
Genetic strength limits could likely go towards silverback gorillas able to lift two tons or even beyond.