Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: mando_vzl on 28/09/2005 19:20:20
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Dear All,
First than all, congratulations on your GREAT program. I am regular listener of your Podcasts from Miami, FL in the USA, and I have found it extremely educational.
My Question is: if all the things in our universe (including us) have been a product of a slow process of evolution, what would be the next evolutionary change in the human race? For instance: will our body be physically different? will some organs such as the appendices disappear? are we goint to have a bigger brain?and such.
Thank you.
Fernando Lárez
FMLG
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Interesting question.
Evolution occurs when there is a selective pressure applied to a breeding population. In other words, genes that help certain individuals to fare better under the prevailing living conditions are more likely to be passed on to future generations than harmful genes.
But there can be a few surprises. Take sickle cell anaemia as an example. This inherited disease causes the haemoglobin in red blood cells to form fibrous aggregates, deforming the cell into a sickle shape. This makes it difficult for the cell to squeeze through small capillaries and can lead to tissues becoming starved of oxygen and glucose. This is bad news.
But the falciparum parasite that causes malaria, and which usually makes red blood cells its home, cannot tolerate the environment in these cells, so people who inherit the gene for sickle cell anaemia are protected from malaria.
For this reason there are lots of people in Africa, where malaria is common, with sickle cell anaemia. But in the UK, where there is no malaria, virtually no one (with the exception of African immigrants) has sickle cell anaemia because it confers no advantage to them in that environment. As a result the gene disappears over time.
Cystic fibrosis is another example. This gene is terrifically common in the white population and is carried by roughly one person in every twenty-five. In order to be present at such a high frequency, given that two copies of this gene affects a males fertility and causes serious ill-health, rather like the sickle gene it must also confer some kind of benefit when present in a single copy. No one knows for sure what this benefit is, but one suggestion is that it might, historically, have provided protection against gut infections like salmonella.
So our future evolution will be shaped and moulded by the environment and lifestyle in which we continue to live. With many more children being born by caesarian these days, perhaps we're destined to evolve larger heads, and possibly bigger brains, or shed the legacy of our cavemen days and shift our metabolism to favour weight loss rather than weight gain (which in the present climate of excess would be an extremely favourable trait !).
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Very though provoking stuff, Mando & Chris.
I think that I would accept the concept that evolution for humans has not ended, but has altered due to differing survival pressure. Unlike most of past human history, the human race in developed nations is now in a situation in which most babies survive to adulthood. I submit that this is an amazing change. In past centuries, human couples who had 10 children, for example, might see 2 or 3 reach adulthood. Now they all will. Does this favor the genes of humans who are prone to having strong religious beliefs, which can sometimes result in large families? Well, maybe, but there is no gene for religious devotion as far as we know.
On the other hand, there are some odd new factors that are applying survival pressure to some human populations. What will be the evolutionary result of HIV? There seem to be a few humans with some degree of genetic resistance to the virus, and theit genes may spread. The prevalance of deadly HIV epidemics in sub-Saharan Africa favors the survival of human there who are strictly monogamous in their sexual behavior. But again, there does not seem to be a gene for monogamy- it's a behavior.
My guess is that evolution will continue, but may become more subtle even than the complicated fuctioning of the sickle-cell anemia gene.
I would like to think that the challenges to the survival of the human race may result in greater intelligence- but it may not pan out that way. Intelligence is not just governed by a single gene, and is also dependent on education. Our societal challenges may also be critical in the next hundred years as the human race struggles to achieve sustainability at a high plateau of population. Evolution is too slow, I think, to handle that challenge.
chris wiegard
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Ah, Chris's post makes a good arguement against some of the people against the idea of evolution who say, "Why aren't we evolving now?" Kudos and props for that, dude!
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If global warming happens perhaps that could cause us to evolve, maybe change out skin to deal with burns. Who knows?
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If global warming happens perhaps that could cause us to evolve, maybe change out skin to deal with burns. Who knows?
Burns happen due to too much sunlight, which is not much to do with temperature (you can get sunburn on a sunny but freezing cold day, but will have no sunburn on a hot and overcast day).
The reduction in industrial pollutants that has happened over the last couple of decades has caused more sunlight to reach the surface, but this change has already come about and is not what people are talking about when the talk about global warming (mostly because they see less pollution as a good thing, and they want to ignore the fact that the pollution also protected us a little from the Sun).
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All of the predictions being made assume that the primary pressure on human evolution is the relationship between the individual and the environment.
I would argue that the dominant relationship that governs human evolution is not the direct relationship between the individual human the the non-human environment, but between the individual human and human society, and between human society and the non-human environment. This is not to say that disease tolerance (such as to HIV) will not happen, but for the most part, the major evolutionary changes are likely to be behavioral, that will make humans function better within human society, and allow human society to better protect the individual. Already, humans are scarcely able to survive outside of a human social context, and in future humans ability to survive away from the human social structures will further diminish, to the point that a human individual would no more be able to survive alone than an ant might survive without the colony of which it is a part.
Even with regard to disease tolerance, most of human disease tolerance has developed not as a consequence of the ability of human individuals to fight diseases (although that has happened to some extent - although the diseases have themselves changed to become less virulent - after all, a dead host is no more use to most disease agents than it is of value to the host to die), but rather tolerance has come about through changes in social behaviour that reduces the ability of the disease to spread through the comunity.
In the long run, it may even be that the ability of the individual to combat disease agents will diminish, as society creates the means to fight disease through artificial means. If we develop ever more effective ways of fighting disease even in the weekest individuals, so the weekest will survive as well as the strongest, and there is no evolutionary advantage for the individual to have a strong immune system, but rather the individual becomes ever more dependent upon being part of a social structure that will provide the means to fight disease agents. Thus, the individual will continue to grow weaker as the society continues to grow stronger.