Are human beings still evolving in response to any recognizable factors?


(Albert Leo) #21

You clearly wrote that both “survival of the fittest” and “environmental conditions” are UNNECESSARY for evolution–not merely that we might put too much emphasis on them. Obviously sexual selection plays a significant role in evolution of animals. Do you re-read your posts before pushing the Reply button?
Al Leo


(Phil) #22

Relax, Leo. I think he saying something like touchdowns are unnecessary in winning football games. Because you still have safeties and field goals. In other words, other means can also be used to effect eevolution, not just those. The English language is can easily be misinterpreted.


(Mark D.) #23

That doesn’t seem like a very influential factor, but I guess the idea is it might concentrate some traits they have in common that way.

Still the biggest determinant would seem to be the desire to make big families. Those who do will pass on their mishmash of traits. Hard to see this coalescing on any other trait.


#24

A relatively recent adaptation in humans is lactase persistence, or the ability of adults to digest milk sugar. This actually evolved independently two times, once in Europe about 9k years ago, and once in Africa about 5k years ago.

This is a very nice short film from HHMI about the rise of lactase persistence and the scientific detective work to understand it. The film is suitable for high school students.

Got Lactase? The Co-evolution of Genes and Culture


#25

We might become more heat-tolerant as the earth warms. And we certainly should try to develop heat- and drought-tolerant crops through selective breeding. Then again, we could become extinct. Have a nice day.


(Mark D.) #26

That is a good example of the sort of adaption I don’t think could be selected for or influence evolution of humans in our current conditions.

I don’t doubt that humans have evolved like every other organism up to now, but it seems as though we are now largely insulated from the process. Not that mutations won’t continue to happen but I don’t see how they can make a difference to who reproduces or how often.


(Steve Schaffner) #27

This is one of those neat findings that has become firmly entrenched scientific lore despite turning out to be completely wrong. It was shown(*) back in 2005 that the evidence for a very recent origin of this mutation, and for positive selection during the Black Death, disappeared with better genomic data. Direct examination of ancient DNA has also shown that the allele’s frequency was the same before the Black Death as seen in the modern population.

(*) The authors included the guy who originally presented the evidence for recent selection. And also me.


(Steve Schaffner) #28

Note that in much of the world, infectious disease is still a substantial cause of mortality, and therefore a significant selective pressure; nutrition is also often inadequate, and adds additional pressures.

In the developed world, selective pressures have changed dramatically. Any heritable traits associated with having more babies (even if the traits don’t directly cause greater fertility) will increase in frequency. With sufficiently large and detailed datasets, it is possible to estimate what some of those traits are. To my knowledge, this has been done for data from Iceland (http://www.pnas.org/content/114/5/E727) and for several datasets from Europe (http://www.pnas.org/content/115/1/151). Short summary: selection is indeed acting on the current population, and it’s making us fatter and stupider.


(Mark D.) #29

Hah! Not too surprising. Perhaps we need to clone a raptor to whip us into shape? But of course infectious disease might well thin our herd from time to time, especially if we fall behind in the antibiotics battle.


(Matthew Pevarnik) #30

Gasp! I thought I could trust the nature blogging educational site.

Good to know thank you!


#31

Yes. We have only wiped out one disease from the face of the earth: smallpox (The virus is extant in the lab.) Human Guinea worm was on track to be wiped out (by President Carter’s foundation) but now there are complicating factors. And there are always emerging infectious microbes, right?

Do you think I’m being too extreme in imagining all kinds of scenarios where humans (and plants and animals) will face selective pressure to evolve? For one thing, there is runaway global warming.


(Lynn Munter) #32

Humans are already pretty adapted to tolerate heat (the list of other animals that could run a marathon in Death Valley is really really really short) and a lot of the global warming dangers probably have more to do with extreme storms, droughts, crop failures and tropical disease expansion anyway.

But isn’t the whole point of the theory of punctuated equilibrium that sometimes a population faces little or no pressure to evolve, at least for a time, and then eventually something changes and a lot of evolution can occur out of the accumulation of genetic diversity that built up over that time?

Because they thought it couldn’t reproduce in animals, but it turned out it could, just rarely, and now it’s in hundreds of village dogs in Chad. Polio is getting close but it’s still uncertain if we will be successful at eradicating it. Pretty interesting stuff to read up on!


(Stephen Matheson) #33

No, I don’t think that’s a very good summary. The main claim of PE is stasis: that species tend to be phenotypically stable, and that most evolutionary change happens in punctuated bursts through splitting of the lineage. PE does not, as far as I know, make claims about genetic diversity or accumulation, and doesn’t claim that stasis results from “little or no pressure to evolve.” Its claim is that “a lot of evolution” is just splitting. You can find a recent discussion of its definition, by one of its founders, here.

And IMO it’s safe to say that this is not an overall theory of evolution and is not particularly well regarded. Gould was rightly criticized for being vague, and even published a major paper that many critics thought undermined his own PE proposal. My personal opinion is that the observation of stasis over time is indeed very interesting and that phenotypic stability is a worthy topic but that PE has not held up as a fruitful overall view of evolution.


(Ryan weatherly) #34

Our global society put a monkey in the wrench , yes we are still developing specialisation (
For hundreds of years, the Bajau have lived at sea, and natural selection may have made them genetically stronger divers.)

But we lack genetic isolation ,

Everybobdy keeps mating with everybody .


#35

Heat waves kill thousands of people every year.

Those are very severe consequences by themselves! But that’s just the beginning. The department of defense is rightly very concerned about global warming. For example, the refugee crisis will become worse as crops fail, and people will become radicalized, both to the left and to the right. And there’s the trivial cost of moving coastal cities such as Manhattan. And on and on it goes.


(Lynn Munter) #36

Worldwide, 20 times more people die from cold than from heat. https://www.sciencedaily.com/releases/2015/05/150520193831.htm

I did not at all mean to imply they weren’t! I think any one of them kills more than the number of people killed directly by heat, which was the only point I was trying to make. Global warming is real and serious and the indirect costs are going to be even more enormous than the direct ones.


(Lynn Munter) #37

Ouch, consider me corrected! :laughing:


#38

Yes, but do you think that colder temperatures are a growing threat? On the very same page as your article we find this: Study of impact of climate change on temperatures suggests more deaths unless action taken. It explains that the death count from hot temperatures is projected to exceed the death count from cold temperatures.

I don’t have the time to list the negative impacts from global warming, and posting articles will only make people mad.


(Lynn Munter) #39

No…just that human adaptation is already pretty far heat-adapted.

I read it carefully and did not see where it said this. It said that deaths from heat would increase more than deaths from cold would decrease, but that’s not the same as saying there will be more deaths from heat than from cold.

I agree with you that the impacts are going to be bad. I was only trying to point out that direct deaths from heat will be the least of our worries, and that we’re unlikely therefore to evolve greater heat tolerance.

What really interests me on the topic is the hypothesis that human evolution was shaped by persistence hunting, or running after large herbivores until they get so overheated they can’t run anymore. It neatly answers the question of how we could have hunted before we developed sophisticated tools and weapons, and explains many features of our anatomy that don’t seem to make much sense otherwise: why are we so hairless? To shed heat. Why do we have such a high capacity for sweating compared to other animals that have to lose heat through panting? So we can run longer without overheating. Why is the hair we have left on the tops of our heads? Insulation from the sun. Why do we have such large gluteus maximus muscles? We don’t need them for walking, but we do for running. Why are our shoulders able to rotate independent of our neck and head and hips? Running. Why did our toes get shorter while the rest of our legs got longer? More efficient running. Why do we have a nuchal ligament for keeping our head stable that looks more like that in dogs, horses, and other running animals than seen in apes or pigs? Running, running, running.

I could go on but I probably shouldn’t!


(Mark D.) #40

I’ve heard about that too and found it interesting mostly because it is unusual to find any physical attribute where we excel over other animals.

@beaglelady, regarding the prospects for human suffering as a result of global warming it doesn’t surprise me to learn that the number of heat related deaths are expected to exceed those from cold. However, we are always cautioned that the chief sign of climate change will be in the number and severity of extreme conditions. Not sure if that would include worse blizzards and cold snaps. But with more heat in the system I suppose not.