I rather be a eunuch rather than to be dead

This NUS study shows how certain male spiders self- castrate rather to be eaten by the female spider.

In “ Why is sex fun”,  Jared Diamond covers why male spider is eaten by the female spider during copulation.

As he puts is,

” This cannibalism clearly involves the male's consent, because the male of these species approaches the female, makes no attempt to escape, and may even bend his head and thorax toward the female's mouth so that she may munch her way through most of his body while his abdomen remains to complete the job of injecting sperm into her.
.....

Suppose that opportunities to transmit genes arise unpre-dictably and infrequently, and that the number of offspring produced by such opportunities increases with the female's nutritional condition. That's the case for some species of spiders and mantises living at low population densities. A male is lucky to encounter a female at all, and such luck is unlikely to strike twice. (1) The male's best strategy is to produce as many offspring bearing his genes as possible out of his lucky find. (2) The larger a female's nutritional reserves, the more calories and protein she has available to transform into eggs. If the male departed after mating, he would probably not find another female and his continued survival would thus be useless. Instead, by encouraging the female to eat him, he enables her to produce more eggs bearing his genes. (3) In addition, a female spider whose mouth is distracted by munching a male's body allows copulation with the male's genitalia to proceed for a longer time, resulting in more sperm transferred and more eggs fertilized. "
.....

In Summary,

“Sexual cannibalism in spiders and mantises is favored by the ecological variables of low population densities and low encounter rates, and by the biological variables of a female's capacity to digest relatively large meals and to increase her egg output considerably when well nourished.”

So what do we make out of this case when the male spider actually chooses to make an escape.  Here are some questions:

• Does the male spider grows back his reproductive organ?  If yes, then this is simply an evolutionary development to have the best of both worlds - leave his reproductive organ to continue to transmit his sperm while growing a new one to impregnate another day.

• If the male spider does not grow back his reproductive organ, this is where everything breaks down and we have to relook the 3 clauses that I highlighted above.

By detaching his reproductive organ and leaving , the male spider continues to enjoy clause 3 of longer copulation time as his sperm continued pumping through the apparatus lodged in their reproductive organs.

But I think the article actually explains why such behaviour evolved:

•  “ the group found that the palps had delivered only a-third of their sperm after the females stopped copulation ...... and there is female-controlled short copulation, and ultimately the female's frequent cannibalism.

Therefore, from the male spider point of view, even if I am willing to be eaten, she copulates for such a short time that perhaps only a third of my sperm is used.

In addition, 

“ the detached palp can prevent other males from mating with the female, thus ensuring the paternity of the self-castrating spider. The eunuch also becomes more aggressive and guards the female from competitors while the sperm is being transferred.”

Mon 22 Jun 2009: 6.30pm – “Darwin, Wallace, and Evolution: Celebrating a major paradigm shift in science” « The Biodiversity crew @ NUS

Mon 22 Jun 2009: 6.30pm – “Darwin, Wallace, and Evolution: Celebrating a major paradigm shift in science” « The Biodiversity crew @ NUS

One of the most pertinent points from the talk:
# Many fossils were found with extinct living things, if God created them (good enough to design), why did he allow them to go extinct?
# Fossils were progressive - from simple plants long time ago then to animals.
# Humans fossils were found only in the upper layer

Skin Colour of Humans and some discrepancies by Jared Diamond.

 

In this article,Race without Colour dated November 1994, Jared Diamond wrote :

“ Among tropical peoples, anthropologists love to stress the dark skins of African blacks, people of the southern Indian peninsula, and New Guineans and love to forget the pale skins of Amazonian Indians and Southeast Asians living at the same latitudes. To wriggle out of those paradoxes, anthropologists then plead the excuse that Amazonian Indians and Southeast Asians may not have been living in their present locations long enough to evolve dark skins. However, the ancestors of fair-skinned Swedes arrived even more recently in Scandinavia, and aboriginal Tasmanians were black-skinned despite their ancestors' having lived for at least the last 10,000 years at the latitude of Vladivostok. “

He goes onto in the article to argue hence it is sexual selection is the reason for our skin colour difference.  It is covered here in a more succinct  article.

I just like to point out though in Chapter 17 of Guns, Germs and Steel, Jared Diamond points out  that the present residents of Southeast Asia, especially Indonesia and Malaysia had come from ancestors who arrived from  Taiwan.

This is the reason why present Indonesians and Filipinos have light skins although the presence of the famous Java Homo Erectus fossils proved that humans have occupied at least western Indonesia for a million years – long enough to evolved tropical adaptations like dark skin. Now only the Philippines  Negritos have dark skin like the New Guineans

Maybe it is just a case  of updated knowledge since Guns. Germs and Steel was wrote many years later.

To answer why the Tasmanians remained dark despite 10,000 years at a high latitude, this page has some answers:

“John suggests that the low genetic variation common among island peoples might be the factor behind why the folks of Oz remained dark. Certainly in the New World there is some variation in skin color among the indigenous peoples, but the tribes of the north remained far darker than equivalent Old World groups (and similarly those of the equatorial regions do not rival Africans, South Indians or Melanesians in complexion).”

Why aren't hereditary diseases removed by natural selection

Answering this question from my dear friend Yingxuan:

Why hasn't hereditary fatal illness been removed by natural selection since the ill should have died and pass down these defective genes?


After talking to my primary school friend who happens to be around, we came up with the following reasons:
1. With modern medical advancements, some of these people managed to live past their reproductive age and actually have offspring.
2. Some of these hereditary fatal illness eg some forms of cancer has actually developed due to the toxics,radiation that we experienced in the modern age.

However, these doesn't answer the question at its most basic level, because modern medical advancement and pollution only happened in the last couple thousand or even hundreds of years, surely with tens of thousands of years we should have eradicated these genetic illness through natural selection?

The reason could be that some of the genes that caused these genetic diseases don't get expressed normally - they stay as genotypes, however when 2 persons carry this same gene gives birth to a offspring - the gene may finally be expressed ( as phenotype) as developing into the genetic disease. Hence there may be lots of people out there who are carrying the genes that cause the genetic disease, but they never get expressed hence natural selection has never got the chance to remove them from our genetic pool.

The above is just musings of an amateur evolutionary biologist.. don't take it for real!