Is Human Evolution Limited by Physical Constraints?

[hitssquad]

Fixing of biological traits - possible or impossible

Even for a single Mendelayev trait, with alleles B and b, where the recessive variation requires a bb gene match to be displayed, having the bb bearers create NO children would still leave half the population (the Bb's) carrying the gene, under equilibrium, and from their mating new bb individuals would continue to be born at a stable rate.

Are you saying the fixing of traits in biological populations is impossible?

 

[Phobos]

Neandertals are actually part of the same species as us- they were Homo sapiens neandertalis.

There has been a debate as to whether Neandertals were a subspecies (as you say) or a separate species (H. neaderthalensis). My understanding is that the mainstream view is that Neandertals were a separate species.

 

[Hwarang]

George washington was tall because he had good nutrition and was lucky enough to receive better height genes. We arnt growing taller though. The Human genome has a maximum limit to how tall we can get. I am estimating the maximum height to be about 7,8 for males and 7,2 for females. Despite this maximum its still possible to get even taller if you suffer from that pituatary gland abnormality(the gland over produces human growth hormone). For example Robert Wadlow who suffered from that condition grew to be 8,11 whiles his genes probally told him that he was only suppose to be around 5,8 in height. Because of this he suffered horrible knee problems and died during his early 30s.

In the future we might see some 1st world nations reach their maximum height with people average in the 7 foot range. This is unlikely though, as height on that range produces a lot of disadvantages.(Buildings will have to be completely re-constructed to accommodate the new taller people, people of that height will have to consume much more food and energy in a world of limited energy and resources, height in that range is much harder to work in and much more clumsy for daily works). In fact I think height will probally decrease in the far future to the 5,5 or less range. I am serious here. Smaller people will consume less resources than much larger people. Which means there will be more smaller people. Which means more brains which means more innovation.

Height for modern first world nations will probally level off at 6,3-5,10 average for males unless a eugenics program is introduced to to purposely increase height to the 7 foot range. Of course certain groups will have taller averages and max heights. Africans will be the tallest. In fact the Tutsi's in Africa averages over 7 foot in height during their peak after selective breeding.

Oh yeah and I found a interesting link regarding neanderthals.

http://en.wikipedia.org/wiki/Homo_neanderthalensis

it says that neanderthals had brains 10% larger than modern humans today. Which is impressive, however the cro-magnons for example had brains 25% larger than modern humans. And don't forget that neanderthals had stronger, heavier bodies which meant more brain was needed to control bodilly functions. Another way to measure intelligence was comparing the tools both sides made. If I remember correctly, the humans made much better tools and had a advantage of unique throwing spearings fire with some wooden shaft which neanderthals didnt. Also there has yet to be a single human with neanderthal genes in them. Neanderthals and Humans could not mate.

 

[tobias087]

I think that because of modern circumstances, some of the conventional rules of evolution will have to be thrown out the window. For example, in the above predictions about the evolution of height in man in the future, it's assumed that reaching a maximum height is economically undesireable because it puts a strain on resources (ie. tall people need to eat more).

However, while this might be a factor for animals in the wild with scarce food supplies, man, in developing countries at least, has no such scarcities. Most people simply do not die from starvation in developed countries in a systematic way caused by food scarcity. If people are hungry, they can easily find more food, at very small marginal cost. Evolutionary economics are a thing of the past. (Not to imply that there aren't hungry people, but even the homeless don't usually die of starvation)

What we should do to examine current trends in evolution is go back to first principles. It would be tempting to list causes of death and declare that humanity will evolve to be less susceptible to these, there's a fundamental flaw there: most of the current leading causes of death (heart disease, cancer, stroke, etc.) are not things that kill people before they have had children. If a cause of death systematically ends people's lives after they've reproduced, then there is no selection pressure to develop immunity to it.

The better approach would be to consider causes of death in the age bracket where people have not yet had children. In the USA for ages 15-24 (which is below the average age of becoming a parent of 25) the leading cause of death is accidents, and the leading type of accident is car accidents, which account for 25% of deaths in this age group. Since food economics are no longer an issue (or are at least only a minor one) we should expect then that people will develop traits that help them survive car crashes (possibly thicker bones or something like that), since that is the main selection pressure in the developed world.

As with regard to the claim that humans are currently in stasis, in between phases of relatively fast evolution, that makes little sense. What we should expect in evolutionary trends is for organisms to evolve to the point where they are best matched for their environment. Then, if the environment stays constant, phenotypes should tend to stay constant since there is no natural selection impetus, disregarding sexual selection and drift. In humans, we do NOT see a constant environment. In fact, our environment has been changing spectacularly rapidly in the last few thousand years (and even faster in the last few hundred). We should expect then, that humanity will evolve rather quickly to meet its new challenges.

Sorry about the long post! Just had a lot to say.

 

[DaveC426913]

Sorry about the long post! Just had a lot to say.

And only five years late...

 

[tobias087]

haha, no time like the present

 

[Bodicea]

I would think that there must be a limit to certain aspects of evolution within the human body. Eg. height. If we evolve into heights of 7 or 8' then how will the heart cope with it. personally I think there is a limit to how tall we can grow.

Intellect? apprently our brains are growing bigger, and its occurred over the last 100 years, but the skull hasnt grown, so the brain is liimited by the the size of the skull, which in turn is limited by the size and strength of the neck. So imho, we are limited physically and intellectually...

However, how we use what we have is changing, and there may well be huge room for development in that area...Are our children actually smarter, or, are they using their brains in a different way due to all the technology that is around. From a very young age they are learning to hone incredibly spatial awareness, hand eye coordination via games consoles...

So, even though there may be physical limitations to our evolution, I'd say there is definte potential for evolution within the confines.