Services Email this article to a colleague Alert me when this article is cited Alert me if a correction is posted Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Download to citation manager Request permission. Sometimes more is better. This raises the possibility that in these cases, trade-offs between sperm number and size influence competitive fertilization success. Secondly, the majority of studies that have examined sperm velocity have reported a positive relationship with fertilization success under both noncompetitive and competitive conditions Table 2. Finally, the relationship between sperm viability and fertilization success is the least well characterized of the sperm traits assessed in Table 2. For example, among primates, female gorillas are relatively monogamous, so gorillas have smaller testes than humans , which in turn have smaller testes than the highly promiscuous bonobos. New insight into the early stages of biofilm formation.
C invest more energy in parenting than do placental animals. Thereafter, the zygote enlarges and remains in the gametophyte, becoming surrounded by a layer of parenchymatous cortical protective cells. Humans are most closely genetically related to great apes, especially chimpanzees. This results in a drastic reduction of the total genetic diversity of the original gene pool.
Alas poor evolutionary psychology. Our larger brains were unable to fit through the birth canal when surrounded by a fully formed, hardened skull. Testing the tradeoffs" PDF. Wikimedia Commons has media related to Evolutionary psychology.
However, there is some evidence that sperm viability influences competitive fertilization success see Table 2. In guppies , a post-copulatory mechanism of inbreeding avoidance occurs based on competition between sperm of rival males for achieving fertilization. Behavioral Ecology 14 — The method used in the fertilizations is classified as either natural matings NM , where males and females mated without interference from the experimenter, or artificial inseminations AI , which also includes IVFs, where sperm were experimentally introduced without matings taking place. However, as several studies have reported a positive relationship between sperm viability and fertilization success, particularly under competitive fertilization conditions, it seems highly likely that sperm viability is indeed an important factor influencing fertilization success. Nature — The Evolution of Desire: