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Questions tagged [reproduction]

The biological process by which new individuals are formed.

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130
votes
1answer
15k views

Do bacteria die of old age?

I know that the cells of mammals at least stop dividing when they are old, and then die a programmed cell death. Then other cells have to replace them. But in a bacterial colony, each cell ...
42
votes
1answer
7k views

Why do human females have periods?

Why do human women have periods when most animals don't? It is known that the unfertilized egg needs to be shed from the uterus. But why shed the whole endometrium? Why didn't evolution put ...
34
votes
2answers
4k views

Why is menstruation in wild animals not a disadvantage to organismal survival?

When I watch wilderness specials for more than a few minutes, I notice a familiar pattern: predators are depicted as being alerted by the scent of blood. Wounded animals seem to make the best prey and ...
31
votes
2answers
5k views

What's the difference between male and female?

As long as we only look at humans the differences are clear: males have chromosomes XY, produce sperm and don't get pregnant. Females have chromosomes XX, produce egg cells and bear babies. But when ...
28
votes
6answers
16k views

Why are not all species hermaphrodites?

If a hermaphrodite animal (like slug, snail, etc) finds a partner they can mate immediately. If another animal with "normal" reproduction (lets say a mouse) finds a partner they can only mate if they ...
23
votes
1answer
567 views

Can a human be made with ovum but without sperm?

This article says that scientists were successful in making a mouse using only a sperm and no egg (ovum). The article also states that this procedure could be applicable to humans. However, I want to ...
22
votes
1answer
1k views

Cells of umbilical cord - mom's or son's?

Let's say we have a mother giving a birth to a son. In a very clear manner the cells of these two individuals are very different, of course. Yet there is an umbilical cord connecting them. Then there ...
20
votes
2answers
1k views

Have we ever observed two drosophila lineages that evolved reproductive isolation in labs?

Background The standard definition of species refers to the concept of reproductive isolation. If two lineages are found to be reproductively isolated, then we consider these two lineages to belong ...
19
votes
3answers
612 views

Are human fetuses more likely to be male? [duplicate]

Question: From a physiological point of view, when sex is determined in a human fetus, is it equally likely to be male or female? Studies in this area typically measure age at birth, where the data ...
18
votes
2answers
8k views

Why do some mammals not have testes in a scrotum?

Coming from an evolutionary approach, Is the only purpose of a scrotum to regulate the temperature of the testes? Knowing all mammals are warm blooded, shouldn't all mammals have testes in a scrotum?...
16
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2answers
1k views

Why do we have more male infants born?

For every 104 male babies, we have 100 female babies and there are statistics which are more reliable. (Those tell us that we have 997 female infants born per 1000 male infants born.) What is the ...
14
votes
1answer
1k views

Can an organism exist as a single cell but come together as multi-cellular during certain times?

I am trying to remember a particular segment from a BBC special, about a single celled species. However, at certain times all the individual cells came together to form a structure, not unlike a ...
14
votes
1answer
2k views

Could humans and chimpanzees hybridize?

In some cases two species can hybridize. For example, Tigers and lions can hybridize to produce "Ligers". Would it also be possible for humans and chimpanzees (or any other species) to hybridize ? ...
14
votes
2answers
26k views

Why is fructose not glucose the main energy source of sperm?

The seminal fluid contains fructose as the main energy source for the sperm and not glucose. Why is fructose and not glucose the primary energy source for these sperm, since glucose is the ...
13
votes
2answers
2k views

Do twins “run in the family”?

My wife and I recently found out that we are going to have twins and so nearly everyone asks if we have a family history of twins. Now I know that the answer for me is that it doesn't matter—as ...
12
votes
2answers
3k views

How was birth control realized in ancient days? [closed]

In ancient days, there were no birth control methods like condoms or contraceptive pills available. How did they control pregnancy?
12
votes
2answers
993 views

Why does the chance of having a baby with Down's syndrome increase with the age of the mother?

Down's syndrome occurs when either the egg or the sperm cell contain on extra chromosome 21. To my understanding, women are born with all the egg cells in place already, so there's no further cell ...
12
votes
1answer
645 views

What bacteria do unborn babies contain?

This Scientific American article states that "[human] infestation [by bacteria] begins at birth". This would suggest that unborn babies are free from any bacteria. However, if the mother catches a ...
11
votes
2answers
983 views

Why, specifically, does each generation, on average, improve upon the design of the species rather than degrade it?

In every non-life example I can envision, a copy of a copy is always a degraded or less pure version of the original unless some outside influence acts to correct the copy back toward the ideal ...
11
votes
3answers
3k views

Species with reproduction barriers that can both reproduce with a third species

To start with, I do not have a sound knowledge in biology or any formal education in the area. I was told that one of the definition of a species is a reproductive barrier, which means that if two ...
11
votes
1answer
5k views

Which sex has higher variance of reproductive rate in modern societies - male or females?

Who has a more varied reproduction rate in modern western societies - men or women? The average rate is the same of course, but I wonder which sex have higher variance - higher variance means that ...
11
votes
1answer
1k views

Why does the sex of the parent species determines the species of a hybrid offspring

I've read a little about hybrid animals, and have been amazed by the fact that the sex of the parent species determine the species of the offspring, in some hybrids. A male horse and a female donkey ...
11
votes
1answer
5k views

Why doesn't ovulation occur in both ovaries simultaneously?

I know that in human body ovulation takes place at only 1 ovary every month. But development of a follicle depends on FSH levels in the blood, and since both the ovaries are exposed to the same blood ...
11
votes
1answer
2k views

Beginning of the urogenital system

Are any invertebrate nephridia (proto/meta) homologous with vertebrate kidneys in the sense that embryologically they also begin together with the genital system? When did the embryologic association ...
11
votes
2answers
2k views

How conscious are mammals that mating leads to pregnancy and offspring?

Does a pregnant female mammal know that its pregnancy is the consequence of a previous mating? Or are humans the only mammals which are conscious of it?
10
votes
1answer
852 views

Is sexual reproduction outside the same biological family possible? Has it ever occured successfully?

Are there any examples of two species taxonomically classified in different biological families that have successfully hybridized and produced viable offspring? If not, is there an example of where ...
10
votes
3answers
2k views

Could a sperm be altered to contain a female's genetics?

While discussing with a friend a while back on the likelihood a futanari (a woman with both fully developed and functioning sets of genitalia) existing in real life, we got into a discussion of ...
10
votes
1answer
3k views

What animal has the longest juvenile period?

I just heard the following complaint from a comedienne. Humans are the only animal that is completely useless for the first twenty five years of life. Obviously this is just a joke but it is true ...
10
votes
1answer
193 views

Gender and age-specific mutation rate in plants

Background General concept According to Cochran and Harpending (2013), mothers transmits on average a number $x$ of new mutations to their offspring. This number $x$ is independent of the age of the ...
10
votes
1answer
5k views

How is centriole number maintained during meiosis?

I've found a website (Pearson's BioCoach) that claims centrioles duplicate in Prophase II. Is this accurate? Does it depend on the species in question? Looking at three textbook illustrations of ...
9
votes
2answers
539 views

Do males ever produce the offspring?

Are there any non-asexual species in which the male of the species produces the offspring? If so, why are they considered male and not female?
9
votes
2answers
8k views

Does our eyeball increase in size as we grow?

Does the size of the eye increase as we develop from the stage the complete eye first forms to infancy and then to adulthood ?
9
votes
2answers
41k views

Can the mating of a couple with Rhesus positive and negative blood types result in miscarriage?

Can the combination of $+ve$ and $-ve$ blood groups of a couple be a cause of miscarriage in pregnancy?
9
votes
1answer
5k views

What will happen if a foetus is Rh- and the mother is Rh+?

If a mother has Rh-negative blood and her foetus has Rh-positive blood it will result in rhesus incompatibility and lead to erythroblastosis fetalis. What will happen if the reverse occurs, when a ...
9
votes
1answer
562 views

What evolutionary pressures pushed Galápagos tortoises to mature so slowly and live so long?

I read that they take up to 40 years (in the wild) to reach the age of reproduction and are thought to live over 100 years, with one in captivity reaching over 170 years. Can someone explain in ...
9
votes
1answer
324 views

What is the main challenge in creating a chemical male contraceptive?

More than 50 years after hormonal contraception for women was invented, a contraceptive pill for males is still not available. With the obvious major biological differences in mind, why does it appear ...
9
votes
1answer
2k views

Can females be recreated from male DNA?

A chromosomal male is XY and a chromosomal female is XX. Now imagine if, one day, this world has only males - is it possible to "recreate" a female by using two X chromosomes from two different males?
9
votes
1answer
2k views

What wasp like insect breeds in clay pots with dead spiders?

I found several small clay pots of oval/cigar shape roughly 2cm long in a rarely used window in the house, because a wasp like insect was flying into a small cavity of the window. I removed one and ...
9
votes
1answer
6k views

How many primary oocytes in human female body at birth?

https://discovery.lifemapsc.com/library/review-of-medical-embryology/chapter-4-gametogenesis-oogenesis In the above site, I see that: About 2 million primary oocytes are found in the ovaries of a ...
9
votes
1answer
11k views

What is the maximum number of babies a human woman can have?

I know you could divide the female fertility period (~40 years, right?) by 9 months which would give something like ~50 kids (with no multiple kids per pregnancy). The limiting factor in this ...
9
votes
2answers
376 views

Why did women historically have such a high mortality rate during birth?

Historically women had a relatively high chance of dying while giving birth. At first thought it seems to me that this would be a disadvantage for the species for the obvious reason that a dead ...
9
votes
2answers
715 views

Why do women live longer than men?

According to Wikipedia and many other sources, women live substancially longer than men (over 5 years in the U.S.). Men can reproduce for much longer than women. So longer living men would have the ...
9
votes
1answer
3k views

A timeline of the odds for survival for fertilized eggs and fetuses

I'm looking for data to build a timeline of the odds for survival of a fertilized egg, i.e., What are the odds it'll last a week? What are the odds it'll last a month? 2 months? (and so on until)...
9
votes
1answer
3k views

Can only fully matured sperm fertilize an egg?

Are only mature sperm able to fertilize an egg? If so, is there typically a reserve of mature sperm that are saved after an ejaculation or does a male need to wait for new sperm to mature before ...
8
votes
1answer
3k views

How does a sperm cell die?

What causes an animal sperm cell to die? Does it die somehow from being outside its original environment? I've studied the Wikipedia page on sperm and I see a lot of information on what makes up a ...
8
votes
2answers
2k views

Why do flowers naturally reproduce with their own species?

I have always wondered why flowers reproduce with the same species naturally. Why can't the pollen grains get to a different species flower through via the wind, water, or insects?
8
votes
2answers
7k views

If a mother had a child with her own son, could a paternity test yield positive result for the son's father?

Let's imagine a family composed of Mr A and Mrs B, who have a son named John. Now, if for whatever twisted reason, John had a child with Mrs B, could a paternity test yield positive result for Mr A ? ...
8
votes
2answers
2k views

Do only one or both pairs of homologous chromatids exchange genetic material during the process of crossing over?

To be specific: Assume chromosomes A and B are homologous. They've both replicated into A1, A2 and B1, B2 and have formed a tetrad at the equator (synapsis). Most textbooks show either A1 and B1 OR A2 ...
8
votes
2answers
1k views

Do hormone drugs affect whether a person feels sexual attraction to males or females?

I know that ingesting testosterone and other hormonal drugs may stimulate libido and increase sexual desire. But I wonder, if a man ingests female hormones such as estrogen, will he experience sexual ...