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By the end of this section, you will be able to:
  • Explain that meiosis and sexual reproduction are evolved traits
  • Identify variation among offspring as a potential evolutionary advantage to sexual reproduction
  • Describe the three different life-cycle types among sexual multicellular organisms and their commonalities

Sexual reproduction was an early evolutionary innovation after the appearance of eukaryotic cells. It appears to have been very successful because most eukaryotes are able to reproduce sexually, and in many animals, it is the only mode of reproduction. And yet, scientists recognize some real disadvantages to sexual reproduction. On the surface, creating offspring that are genetic clones of the parent appears to be a better system. If the parent organism is successfully occupying a habitat, offspring with the same traits would be similarly successful. There is also the obvious benefit to an organism that can produce offspring whenever circumstances are favorable by asexual budding, fragmentation, or asexual eggs. These methods of reproduction do not require another organism of the opposite sex. Indeed, some organisms that lead a solitary lifestyle have retained the ability to reproduce asexually. In addition, in asexual populations, every individual is capable of reproduction. In sexual populations, the males are not producing the offspring themselves, so in theory an asexual population could grow twice as fast.

However, multicellular organisms that exclusively depend on asexual reproduction are exceedingly rare. Why is sexuality (and meiosis) so common? This is one of the important unanswered questions in biology and has been the focus of much research beginning in the latter half of the twentieth century. There are several possible explanations, one of which is that the variation that sexual reproduction creates among offspring is very important to the survival and reproduction of the population. Thus, on average, a sexually reproducing population will leave more descendants than an otherwise similar asexually reproducing population. The only source of variation in asexual organisms is mutation. This is the ultimate source of variation in sexual organisms, but in addition, those different mutations are continually reshuffled from one generation to the next when different parents combine their unique genomes and the genes are mixed into different combinations by crossovers during prophase I and random assortment at metaphase I.

Evolution connection

The red queen hypothesis

It is not in dispute that sexual reproduction provides evolutionary advantages to organisms that employ this mechanism to produce offspring. But why, even in the face of fairly stable conditions, does sexual reproduction persist when it is more difficult and costly for individual organisms? Variation is the outcome of sexual reproduction, but why are ongoing variations necessary? Enter the Red Queen hypothesis, first proposed by Leigh Van Valen in 1973.

Leigh Van Valen, “A New Evolutionary Law,” Evolutionary Theory 1 (1973): 1–30

The concept was named in reference to the Red Queen's race in Lewis Carroll's book, Through the Looking-Glass .

All species co-evolve with other organisms; for example predators evolve with their prey, and parasites evolve with their hosts. Each tiny advantage gained by favorable variation gives a species an edge over close competitors, predators, parasites, or even prey. The only method that will allow a co-evolving species to maintain its own share of the resources is to also continually improve its fitness. As one species gains an advantage, this increases selection on the other species; they must also develop an advantage or they will be outcompeted. No single species progresses too far ahead because genetic variation among the progeny of sexual reproduction provides all species with a mechanism to improve rapidly. Species that cannot keep up become extinct. The Red Queen’s catchphrase was, “It takes all the running you can do to stay in the same place.” This is an apt description of co-evolution between competing species.

Questions & Answers

What's the function of epiglottis
Ugo Reply
What Is The Other Name For Intestinal Juice?
Justin Reply
what is the largestest planet of the universe
rick Reply
what are the types of cell
Bernard Reply
prokaryotic and eukaryotic
prokaryotic cell and eukaryotic cell
what is the protein found in the blood?
Tobias Reply
what is parasitic movement
Emmanuel Reply
Parasitic movement is a problem for all of us. So is its companion, parasitic tension. Parasitic movement is the excess contraction of muscles that you don't actually need to complete an action.
HW a u
am OK how a u
absorption may simply mean utilization of food in the body
what are eukaryotic cells
Thiza Reply
eukaryotic cells which posses a true nucleus that is the DNA is enclosed and covered by a nuclear membrane
what is the mean of pair of chromosomes
Kazula Reply
23 haploid and 23diploid
how are you studying in this quarantine? .. how are you keeping yourselves motivated?
sivajijadhav @815.com
good morning guyz
tell me if you know what can be used...than reading pls hint me pls 🙏🙏🙏
what is the important of sex
Aremu Reply
why did human being need sex?
because he/she have feelings
reproduction...to make more
due to active harmon
One important of sex is to reproduce
to ensure the countinuty of life
all of you are right
for sexual satisfaction and birth
what is momentum
Asiya Reply
The strength or force that allows something to continue or grow stronger or faster as time pass
What is Centripetal Force?
centrepital force is the inward force required to keep a body moving with constant speed in a circular path
what is the test for protein
Takii Reply
List four condition necessary for seed germination
Tedeka Reply
water, light, oxygen and temperature
water, oxygen, light temperature
water oxygen light and temperature
importance of biology
Alabina Reply
importance of boilogy
what is soil
Amina Reply
soil is the upper part of the earth
what is importance of studying biology
soil is the uppermost layer of the earth on which plant grows
soil is defined as the thin surface of the upper most layer of the earth crust on which plants grow
soil is the upper part of the earth which plants grow on
soil is the uppermost layer of the earth in which most of the necessary nutrient are found and serve as habitats for some organisms
soil is the uppermost layer of the earth in which most of the necessary nutrients are found and serve as habitats for some organisms
soil is the uppermost layer of the earth in which most of the necessary nutrient are found and serve as habitats for some organisms
soil is the uppermost layer of the earth in which most of the necessary nutrients are found and serve as habitats for some organisms
soil is the accumulation of lose weathered materials which covers much of the land surface of the earth

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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